Small radius firing pin stop for 1911s


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1858
June 11, 2013, 09:17 PM
I've read a number of threads in which 1911Tuner discusses the small radius firing pin stop so I figured I'd try one in my Kimber. In the process I discovered that both of my Dan Wessons have factory installed small radius firing pin stops (shown on left). I ordered a Wilson Combat Square Bottom Firing Pin Stop (http://shopwilsoncombat.com/Firing-Pin-Stop-70-Series-Square-Bottom-Bullet-Proof-Stainless/productinfo/399S%2C70SQ/) last week and it has a tighter fit in the Kimber slide compared to the large radius Ed Brown stop I've been using (center). The firing pin wasn't clocking much, if any, but now it's even less able to rotate. 1911Tuner has mentioned an ideal radius of around 0.063" on the bottom of the firing pin stop so I had that number in my head as I got to work. I shot the pistol today and my first impression is that the pistol feels "better" under recoil. Case ejection feels like it's been smoothed out and is less "snappy". Also, muzzle rise under recoil is definitely reduced and I felt a noticeable difference in the speed of follow up shots. The pistol has been very reliable but now it just feels ... better. 1911Tuner has made the point that he's all about reliability and that the reduction or change in felt recoil is a secondary benefit. All in all I'm very pleased with the changes and will upgrade my EBs with this simple little piece. Thanks 1911Tuner for the tip.

http://thr.mcmxi.org/pistols/kimber/teii/photos/fps_01.jpg

http://thr.mcmxi.org/pistols/kimber/teii/photos/fps_02.jpg

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huntershooter
June 12, 2013, 06:10 AM
Interesting.
I also installed these on a few of my 1911's (and a couple P-35's).
Subjectively, I DID notice a difference in the perceived recoil impulse in a 9mm 1911. Shooting +P handloads the shot to shot "felt" perceptibly "better"/smoother.
I did not notice much of a difference with the .45, shooting nearly identical pistols side by side-one with, one without the FBFPS.
The P-35 probably benefited the most in felt/perceived recoil.
I think the mechanical advantage (actually "disadvantage") gained by using the part is well worth the effort.

1911Tuner
June 12, 2013, 07:45 AM
25 people showing up to tell you that it's all in your mind in 3...2...1...

:D

While I never said that a 1/16th radius is ideal, mine usually turn out around that. I actually don't shoot for a specific dimension, but just cut a light bevel, and then swipe the stop on a stone until a radius starts to come up...and then install it and let nature take its course.

At this point, it might be good to revisit the point that this isn't a recoil reduction trick. It's about reliability, and any difference in felt recoil is incidental. The reports vary from pistol to pistol and shooter to shooter.

One thing that seems to remain constant is the reports of faster followup shots and shorter split times, regardless of any detectable difference in muzzle flip or felt recoil. Often these reports are much like 1858's...that the gun just somehow "feels" better...smoother...or "different." That's an indication that something is going on, whether or not we can actually put a finger on it.

smalls
June 12, 2013, 11:05 AM
I'm not sure I understand what you did there. Are you talking about beveling the bottom inwards towards the slide?

And Tuner- you said this job is all about reliability. What sort of problems is this a solution to?

VetPsychWars
June 12, 2013, 01:47 PM
Wasn't the story that the larger radius stop was implemented because some people found the slide hard to pull back when the hammer was not cocked first?

I would be very interested in seeing an analysis of changes in function that resulted in ergonomic changes to the pistol.

Tom

vba
June 12, 2013, 02:38 PM
1911Tuner could correct me, but I believe the original firing pin stops in the 1911 were flat or non-rounded. I agree that rounding the FPS was done to make the slide easier to cycle.

I installed EGW firing pin stops on a couple of my 1911's as it keeps the gun from unlocking too early. I did this because I was shooting 255 grain 45 Colt bullets at ~850 to 925 fps. The guns show no sign of over pressure and cycles very well. The guns will also fire 200 grain SWC and 230 grain FMJ bullets without any ill effect from the flat firing pin stops.

VetPsychWars
June 12, 2013, 02:44 PM
I confess my interest is in shooting my 10/18 Model of 1911 in a manner that is consistent with preservation. (It's not collectible and even if it was, "not shooting it" is not an option.)

For example, with a new mainspring and a Gold Cup recoil spring, the slide moves so slowly during the firing cycle I swear you could hold the gun with two fingers, lightly.

So I'm interested in the effects of a smaller radius on the firing pin stop (there was one there originally, by the way) on the rearward slide velocity.

Tom

hariph creek
June 12, 2013, 02:46 PM
I run a EGW flat FPS on my Kimber. Very flat, just barely "broke" the corner.
But then, it's a 10mm. This lengthens dwell time, allowing pressure to bleed off, slowing the rearward slide velocity. It works better than increased weight springs, without as many side effects.

Drail
June 12, 2013, 03:00 PM
You want to be really amazed go from a standard 1911 to a bull barrel AND a squared FPS. It is literally like shooting a different gun. You too can be a hosemaster.

huntershooter
June 12, 2013, 03:35 PM
Obviously a moderately radiused FPS has/gives-a mechanical advantage to the rearward movement/reciprocation of the slide (i.e. a "stock" FPS).
A Flat Bottom FPS does not have that mechanical advantage; the slide has to "work harder" to overcome the lack of mechanical advantage the radiused stop provides, to cock the hammer/compress the MS.
I would reasonably assume this slows, or retards the slide velocity at it's rearward most position.
I would also assume this would: cause less "battering" to the frame, allow the use of lighter recoil spring, or hotter ammo with standard recoil spring (certainly in the case of the P-35/9mm +P).

I'll add that a CZ-75 of mine came "stock" with a FBFPS.
This 9mm pistol is rated for +P and Nato ammo.
The recoil spring in the pistol feels like 14#. The MS is equally light.
Although this pistol is heavier and arguably more robust than a P-35/BHP, I found it interesting that the primary difference between the CZ-with light recoil and MS, which is rated for +P, compared to the P-35 with 28-32# recoil spring and HEAVY MS is the FBFPS.
In my mind I see that as definitive proof the FBFPS retards the slide velocity.

VetPsychWars
June 12, 2013, 05:04 PM
Considering the recoil spring is acted upon directly versus the much stiffer mainspring being compressed by tiny actions of a very small lever, I would hazard a guess that, for the rearward portion of the slide travel, the recoil spring might as well not be there.

Or rather, the recoil spring doesn't do much except during return to battery.

Tom

1911Tuner
June 12, 2013, 05:14 PM
What sort of problems is this a solution to?

It's not a solution to any specific problem. It delays and slows the slide a little and gives everything time to catch up...like the magazine...and it softens the slide to frame impact a little without resorting to heavy springs, which can bring their own particular set of issues to the table.

1911Tuner could correct me, but I believe the original firing pin stops in the 1911 were flat or non-rounded.

Browning's original radius was .078 inch...or 5/64ths...which is a little larger than my personal preference of about 1/16th. And yes. It was changed to the now standard 7/32nds by the Army Ordnance Board in January 1918 after complaints of the slide being difficult to cycle with the hammer forward.

Considering the recoil spring is acted upon directly versus the much stiffer mainspring being compressed by tiny actions of a very small lever, I would hazard a guess that, for the rearward portion of the slide travel, the recoil spring might as well not be there.

Or rather, the recoil spring doesn't do much except during return to battery.

The locked breech pistol can be fired without a recoil spring present at all without ill effect. For those who want to put it to the test...use a FLGR and plug because the standard guide rod will cant upward and tie up the gun, maybe doing some damage in the process...and be sure to realign the bushing with the plug between shots.

And, yes. The "recoil" spring's function is returning the slide to battery. Whatever else it does is incidental and irrelevant.

Scimmia
June 13, 2013, 12:10 AM
And, yes. The "recoil" spring's function is returning the slide to battery. Whatever else it does is incidental and irrelevant.

Incidental, yes, but not irrelevant. It changes the way the gun acts, that's never irrelevant.

1911Tuner
June 13, 2013, 06:31 AM
Incidental, yes, but not irrelevant. It changes the way the gun acts, that's never irrelevant.

Irrelevant to the function of the pistol during the firing phase. i.e. Without the spring, there is no early unlocking, nor is there any destructive frame battering. Other than having to manually return the slide, nothing at all changes to any significant degree.

1911Tuner
June 13, 2013, 11:07 AM
I would have liked to see a more in depth discussion on why you feel it's OK to deviate from JMB.



Many years ago, after discovering the effects of the original 5/64ths radius vs the now standard 7/32nds...I decided to take it a little further and see what happened. An experiment. In those days, I had to make my own stops, and the unfinished units had square bottoms. So, I tried it with a little smaller dimension and it worked well with no adverse effects, so I've stuck with it.

Greg528iT
June 13, 2013, 11:15 AM
I noticed last night my STI Spartan IV 9mm has a straight taper from bottom to near the firing pin. I didn't remove and measure it. I'm still mulling the dynamics of it. Probably very close to the large radius, but that seems too simple. It's probably lost in the noise of everything going on. Easy pull of the slide on a down hammer that transitions to a harder push faster..

jmorris
June 13, 2013, 11:15 AM
I would have liked to see a more in depth discussion on why you feel it's OK to deviate from JMB.

Even I can answer that one, to make it better.

You would have to hunt for a pistol that is a copy of the original. Almost all of the 1911's you can find these days are "improved" versions. Not to mention the winning records in the shooting sports of the double stack "2011" style pistols.

1911Tuner
June 13, 2013, 11:30 AM
I noticed last night my STI Spartan IV 9mm has a straight taper from bottom to near the firing pin. I didn't remove and measure it. I'm still mulling the dynamics of it.

Some installers taper the stop in one direction or another. Due to variations and tolerance stacking in some few pistols, the stop needs a negative rake...narrower at the top...in order to maximize the stop's effect in delaying the slide. IMO, that's a bit over the top, and I've never found a real reason to do it on an ordnance spec pistol. STI's specs may require a little massage. Since I've never examined one of theirs, I can't make a call as to why they did that, but there must have been a reason. Maybe it was as simple as getting the hammer face to strike the stop dead flat. Maybe it was done to increase the mechanical advantage to prevent short recoil.

VetPsychWars
June 13, 2013, 11:33 AM
Even I can answer that one, to make it better.

You would have to hunt for a pistol that is a copy of the original. Almost all of the 1911's you can find these days are "improved" versions. Not to mention the winning records in the shooting sports of the double stack "2011" style pistols.
Indeed true, just on dimensions alone: my Remington R1S is larger and heavier than my Colt Model of 1911. I sort of wish it weren't as it's my carry gun!

Tom

Jim Watson
June 13, 2013, 12:08 PM
I am about done shooting hardball or even Major power factor reloads, my comfort level is down about 9mm and .45 Midrange.

Now while it is possible to go with conventional setup, just less spring, for those lighter loads, there is a brand of hammer/sear/fp stop that goes in the opposite direction to the small radius approach. It has a large radius on the fp stop and a scallop out of the hammer below the striking face so as to reduce the mainspring resistance to the slide.
That lets you use more recoil spring that will more positively strip rounds off the top of the magazine. A real speed shooter will want to do some trials to see what combination shoots the "flattest" but I am after reliability and comfort.

Greg528iT
June 13, 2013, 12:55 PM
Now while it is possible to go with conventional setup, just less spring, for those lighter loads, there is a brand of hammer/sear/fp stop that goes in the opposite direction to the small radius approach. It has a large radius on the fp stop and a scallop out of the hammer below the striking face so as to reduce the mainspring resistance to the slide.

which seems to be at polar opposites of your position as to why a small radius is better.

flightsimmer
June 13, 2013, 01:30 PM
I installed a squared off firing pin stop in my Delta Elite 1911 to help delay the slide opening by just a few miliseconds so the pressure could drop enough to prevent bulged cases which were not a problem anyway but I wanted to remove the stock slide return springs and install standard 1911 spring for ease of manipulation of the slide.
It worked good and I've had no problems of any kind.
It was completly square when I got it and all I did was polish it on a stone to a very tiny smooth radius.

1911Tuner
June 13, 2013, 01:41 PM
which seems to be at polar opposites of your position as to why a small radius is better.

The firing pin stop radius can be used as an aspect of tuning a gun to a specific load. If the recoil impulse is too low to provide a strong cycle, there are several approaches we can take. We can drop the recoil spring a few pounds, and it the return to battery is good, then we stand with it. If not, we go to the mainspring. If ignition is reliable and it works, it works. If not...we turn to the larger firing pin stop radius and go back to the stronger recoil and mainsprings. I used a larger than the now standard radius when I set up a .45 pistol for my small daughter to use.

Tuner, Why are you wasting web space responding to me about you deleting my post?

Because, even after an explanation and an attempt to guide and direct you on how to ask a question, you can't seem to let it go.

But...very well. Go back and have another look.

Let it go, Greg.

Greg528iT
June 13, 2013, 02:24 PM
That lets you use more recoil spring
This is a polar opposite to your normal 1911 protocol, is it not?

1911Tuner
June 13, 2013, 02:41 PM
Jim wrote:

That lets you use more recoil spring

And Greg wondered:


This is a polar opposite to your normal 1911 protocol, is it not?

Greg...at this point, I don't know if you're failing to read...failing to understand...or just being contrary. I'll give you the benefit of the doubt here assume that it's one of the first two.

Read carefully. I answered this in post #23, but apparently I wasn't clear enough. I'll try again.

When the ammunition is so light in power and recoil that the slide won't cycle cleanly with a standard recoil spring, the first approach is to lighten up on the spring. If the pistol then starts having return to battery issues because of the light spring...we go back to the stronger spring and lighten up on the mainspring. If the lightened mainspring starts giving ignition failures...we go back to the mainspring that DIDN'T give ignition problems and turn to using a larger radius on the firing pin stop in order to INCREASE the slide's mechanical advantage in overcoming the mainspring, and lowering the overall velocity and momentum requirements to get the slide to make full travel rearward.

Using the larger than standard radius is all about tuning the gun to function reliably with a reduced load.

Greg528iT
June 13, 2013, 02:48 PM
The post indicated using MORE than standard..
You are talking about going lighter and then if required going to MORE.. You do not say more than standard.

Every other post on this forum you repeat about NOT having to go to the heavier recoil springs, it's a fix that masks the initial problem.. thus for someone to suggest to move to a heavier recoil spring (from standard) is opposite of your general console.

I am being a bit pig head causes you delete posts. You must have some problem with me pointing out that you are differing from JMB original design. Me personally I THINK that is should be adjust some for today's situations. I am trying to dispel the "It has to be exactly like JMB designed it. It's OK. LOOK even Tuner does it"

1911Tuner
June 13, 2013, 03:02 PM
The post indicated using MORE than standard.

Jim's post was pretty clear. I understood what he meant. If you'll go back and read it again...all of it...carefully...it'll be clear for you, I suspect.

You must have some problem with me pointing out that you are differing from JMB original design.

And I offered a detailed explanation on that, too...or did you not read it?

Condensed version:

I varied from the original radius by .0156 inch and didn't notice any detrimental effect...so I stuck with it. Do you know how small a difference that is?

Why?

Basically because I'm lazy and it's easier and faster to cut a light bevel and roll it on a stone than trying to mill or file a precise radius. It might be a .062 on one... .070 on another one...and it might be .055 on yet another one. As long as it's a small radius, I don't get too tangled up in minor details.

Greg528iT
June 14, 2013, 03:01 PM
Going back and re reading.. I see there is a paradigm shift required.
When I talk about springs or other similar objects I would use 3 distinct terms. Normal, weaker, and stronger or variations to that theme.. ie. stiffer = stronger.

When I read that Jim said he went to a lower (softer, weaker) spring.. then moving to a stronger (stiffer) spring.. Now while the Normal spring is stiffer than the softer spring I was expecting it to say.. "... moving back to the normal spring..." if that is what he meant by stiffer than the soft.
When I read he moved from the softer to stiffer springs, I read. jumping over the normal spring.

Greg528iT
June 14, 2013, 03:07 PM
Why?

Basically because I'm lazy and it's easier and faster to cut a light bevel and roll it on a stone than trying to mill or file a precise radius. It might be a .062 on one... .070 on another one...and it might be .055 on yet another one. As long as it's a small radius, I don't get too tangled up in minor details.

This is more detail than previously given. The type of detail I am looking for.

Since this thread has started, I'm considering picking up a Wilson small radius stop. It's only $19... Once I do, I would look / measure it.. compare.. maybe tinker. My current 1911s are running great, but hey I can always put the original back in.

When I 1st started reading this, my 1st thought was.. would too sharp an edge on the stop cause a fatigue issue for the hammer??? I expect the steel of the stop is soft enough it'll knock the edge off pretty quick, but would the 1st couple shots cause the sharp edge in the hammer that could propagate???? (wondering out loud, as I can't see putting one in, without an eased edge)

1911Tuner
June 14, 2013, 05:26 PM
would too sharp an edge on the stop cause a fatigue issue for the hammer???

No. Ned Christiansen runs the EGW stops in his 10mm custom builds as they come...square. Even the square bottom has a radius. It's just a very small one.

One thing that you do have to look for when you leave one square is that the hammer face will strike flat on the stop. Some aftermarket hammers may contact the square bottom and cause ignition problems. I ran into that once. Can't remember who made/marketed the hammer, but it was one of those skeletonized "racegun" type hammers. A light bevel on the corner set it right.

I expect the steel of the stop is soft enough it'll knock the edge off pretty quick.

They're not really any softer than the hammers as far as I can tell. I've been running the same ones in my dedicated range beaters for years and a lot of rounds, and I can't see any change other than polishing.

I'm considering picking up a Wilson small radius stop.

The advantage with the Wilson is that it's pretty much a drop-in. The radius is whatever Wilson decided on. The advantage with the EGW is that it's oversized and allows the installer to fit it closely to the slide and the extractor...stabilizing the extractor and making ejection more consistent...and the square bottom lets you set the radius as small as you want.

This is more detail than previously given.

It's nothing new. Since the subject of the stop radius first came up here about 7 or 8 years ago, I've always maintained that going for a precise dimension is unnecessary unless the object of the exercise is to exactly duplicate the original...and even that has a +/- tolerance of .005 inch. I'd have thought you'd have run across that by now.

1858
June 14, 2013, 06:04 PM
The Wilson firing pin stop that I linked to in my first post doesn't really have much if any radius at the bottom. The photo on their website is misleading. It was a good fit in my Kimber slide and a fair bit tighter than the Ed Brown stop it replaced. As I mentioned before, Dan Wesson 1911s use a small radius firing pin stop. That might help explain why my V-Bob feels like it shoots softer than my EB SF Carry. That and the difference in recoil spring weight. EB uses a 20lb spring but the V-Bob Wolff spring is 16lb or less. I can see lots of changes ahead.

Greg528iT
June 14, 2013, 06:19 PM
One thing that you do have to look for when you leave one square is that the hammer face will strike flat on the stop
Gotcha. I'll spread some transfer ink and see what the hammer strike surface pattern is.

They're not really any softer than the hammers as far as I can tell.
I was unsure of what the various new parts were going to be made to. Hammers, with the hammer hooks often are sold being from a harder tool steel, for "as they promoted" longer hammer hook wear. When I hear HARD, I think brittle though it all relative of course. Good hard tool steel is not so much brittle like glass but more brittle than lead.

The Wilson I saw said. oversized. How oversized is of course subjective. So the EGW is for sure needing to be fit. Good to know.

This is my 1st foray into firing pin stops. Again my 3 active 1911s run very well. This is about figuring something new out.

1911Tuner
June 14, 2013, 06:35 PM
I'll spread some transfer ink and see what the hammer strike surface pattern is.

You'll probably be able to look between the stop and the hammer face and see if there's a problem. If you can see firing pin, the bottom of the stop is contacting the stem of the hammer before it goes full forward. Use a good light. Unless you use a rooneygun hammer, it won't likely be an issue, and even then only on certain guns. Tolerances stack in the wrong direction sometimes.

Greg528iT
June 14, 2013, 07:23 PM
Yeah, probably be able to see it ok with a bright light.

Looking back at the original picture I see why my brain jumped to the fatigue issue. The stops are all dented by the hammer. The force of recoil being more than that of the hammer falling............. but being in contact when the impulse starts is probably what saves it.

Fred_G
June 14, 2013, 08:50 PM
I have never heard of this. After reading Tuner's explanations, it does seem to make some sense. Would this one be the one to get? http://www.midwayusa.com/product/189437/wilson-combat-bullet-proof-firing-pin-stop-with-square-bottom-1911-45-acp-series-70-stainless-steel

My 1911 is a series 80 set up as a series 70 safety, if that makes any difference.

1911Tuner
June 14, 2013, 09:26 PM
Looks like it, Fred. Probably an EGW. I didn't know that Wilson's came with a square bottom. From what I'd heard...and seen on a couple of Wilson's recent pistols...the stops came with an original-spec radius in place.

Or maybe my memory is failin' like everything else...

If I was a dog, they'd probably wanna put me to sleep...

Remember that Series 80 stops are different than original, or so-called Series 70 stops. Make sure to get the right one.

It's funny. Before the subject of the original firing pin stops and the small radius first emerged, the only pistols that I'd ever seen'em on were original GI pistols made before January 1918 that had escaped the change to the 7/32nds radius stop, and original commercial/civilian Government models of the same era. Now, it seems like everybody has jumped on the bandwagon, with some...like Wilson Combat...installing them as SOP.

Interesting.

I guess they do watch these boards.

And it all got started over on M1911.org after I cobbled one up for the owner and shipped it to Greece. He started a thread on the amount of recoil reduction it produced, and it lit off like a Roman candle. I now see it mentioned on boards that I've never visited.

The originals were so hard to come by that at one point, I was forced to make my own stops so I could use a small radius. I had access to a fully equipped machine shop at the time, so it wasn't hard to arrange. I could set up and cut'em in multiples. Then, when I retired and lost access to the shop, I was forced to use the mill function on a Shop Smith...which ain't exactly a precision setup. I had to leave enough material to finish to dimension with a file...which was a drag.

When EGW stops made the scene, I breathed a happy sigh, because they saved me a ton of work, and I owe George a big thanks.

Fred_G
June 14, 2013, 09:59 PM
Thanks for the info, will look into what series 80 one to buy.

Coltdriver
June 15, 2013, 12:50 AM
I picked up a Colt Compact Officers in .45. Had lots of concerns about making it reliable and figured it was just too much bullet pushing too little slide.

So I read 1911Tuner's advice, installed a 24 pound hammer spring, a flat bottomed FPS and added a full length guide rod (just to add friction) with a flat wound spring.

Mine is a total pleasure to shoot and has turned out to be very reliable. I do run good Colt Magazines.

Between all of the pieces (I very marginally knocked the edge off of the FPS, just smoothed it really) they reduce the speed of the slide movement, give enough time for the mag to push another round into place and just make it easy to shoot with a very noticeable reduction in the snappiness of the unmodified version.

1911Tuner
June 15, 2013, 07:34 AM
Ah! The Officer's Models. They present some unique hurdles sometimes.

The main one is getting that low mass slide to strip another round and get it into the chamber. That's why they have such stiff springs. The other one is the short runup...distance...to the magazine from the starting point after it hits the impact abutment.

I've had good success at getting the delinquents to run, but a few were real head-scratchers.

Whenever the OM subject comes up, I'm reminded of a poem that I heard years ago.

"There was a little girl who had a curl in the middle of her forehead. When she was good, she was very good...but when she was bad, she was horrid."

By the way, as a point of interest...In the 6-round magazines with the flat, dimpled followers...the springs and followers are identical and interchangeable with the standard 7-round magazines with the flat dimpled followers. The Wolff 11-pound/7-round spring can be used. More than any other variant, enough magazine spring is critical. The Wolff spring in the magazine cures a lot of OM ills.

Fred_G
June 15, 2013, 11:06 AM
Ordered a EGW series 80 firing pin stop. Bout $20 shipped. Will see how it does.

cauldron
June 15, 2013, 12:16 PM
I had to look it up, and it looks like Colt started making the 'black Army' pistols in the middle of 1918.

So if the change to the radius was in January of 1918, there would be a few 'black Army' pistols with the small radius stop. (I think)

So now I won't feel chagrined putting a small radius stop on my Colt 01918 reproduction!;)

1911Tuner
June 15, 2013, 12:35 PM
So if the change to the radius was in January of 1918, there would be a few 'black Army' pistols with the small radius stop.

Nope. They implemented the change about 6 months before the "Black Army Colt" appeared.

cauldron
June 15, 2013, 01:15 PM
Well... poop. Wikipedia failed me again. :(

Greg528iT
June 15, 2013, 02:13 PM
As a possible side effect.. As I stated before, my STI Spartan IV 9mm has a straight chamfer stop. It has a maybe 1/32" bottom surface. NOT enough to really put any radius on it. The edge looks to be just the machined edge, nothing horribly sharp.

When I re assemble the slide, the stop has always hit the disconnector and STOPPED, I'd have to apply more than normal force. A bit more than my other 1911s.
There is no radius to help cam the disconnector down. It's not a show stopper, but, if one decides to try a very small radius pin stop, a new hiccup might be in putting the slide on.. is probably the disconnector not wanting to cam down as easy. I just pushed the disconnector down with a screw driver so it was all just a smooth slide together motion.

1911Tuner
June 15, 2013, 05:40 PM
When I re assemble the slide, the stop has always hit the disconnector and STOPPED, I'd have to apply more than normal force.

Sounds like you need to hit the bottom of the firing pin stop with a smooth mill file and cut it flush with the center rail then establish a light bevel to act as a cam. Got a picture?

NacsMXer
June 15, 2013, 10:56 PM
1858, thanks for your post and sharing your experiences.

I have a Kimber as well and am interested in fitting one of these Wilson stops. Could you please explain in detail exactly how much fitting was involved?

i.e. did you have to make the overall thickness thinner by sanding the entire backside? did you have to sand the sides a good bit to fit the extractor? did you need to remove a lot of material or a little?

Thanks!

1858
June 15, 2013, 11:08 PM
NacsMXer, I didn't have to remove any material. All I did was put a small radius on the bottom of the stop. It fits very well and the Ed Brown extractor I'm using has just the slightest bit of movement.

NacsMXer
June 15, 2013, 11:36 PM
Thanks 1858. I'm going to give one of these Wilson stops a try in my Grand Raptor II. I have always wanted to try the EGW oversized square bottom FPS, but have been leary of being able to correctly fit it to my slide.

This next question is for 1911Tuner, or anyone knowledgeable on the subject. I run a reduced 19lb Wolff mainspring in my GRII to complement my trigger job/Harrison Design internals. I am currently running a 1lb heavier Wolff 17lb recoil spring to compensate for the reduced mainspring. I shoot traditional 230gr full house ball.

If I install a flat bottom stop, should I go back to a standard 16lb recoil spring or keep everything the same?

Thanks and sorry, don't mean to hijack the thread.

Greg528iT
June 16, 2013, 01:47 AM
Sounds like you need to hit the bottom of the firing pin stop with a smooth mill file and cut it flush with the center rail then establish a light bevel to act as a cam. Got a picture?

I'll probably hit the edge a bit, but as you can see there is not a lot of room to make a bevel or radius very big. I'll probably get an EGW and start from nearer to scratch.

http://i1177.photobucket.com/albums/x349/jaggoett1/2013-06-15212328_zpsafad8037.jpg (http://s1177.photobucket.com/user/jaggoett1/media/2013-06-15212328_zpsafad8037.jpg.html)

http://i1177.photobucket.com/albums/x349/jaggoett1/2013-06-15212235_zps583f1374.jpg (http://s1177.photobucket.com/user/jaggoett1/media/2013-06-15212235_zps583f1374.jpg.html)

It's flush with the center rail.

It might be a thing of.. done cause they can. Short of assembling the slide it seems to be fine.

harrygunner
June 16, 2013, 01:56 AM
I have a flat bottom firing pin stop (FPS) in my 10mm 1911. 'tuner' is a pretty good physicist, so I'm throwing this out there for his consideration.

When I first heard of this, the effect of the shortened moment arm on the force against the slide was obvious. But then I got to thinking the grip housing mainspring is compressed the same amount no matter the shape of the FPS by time the hammer locks back. So the net change in kinetic energy of the slide would be the same.

Then, I realized the square cut on a 'firing pin stop' alters the shape of the curve of work the slide does as it pushes the hammer back, forcing the slide to transfer more energy into the mainspring at the beginning of the slide's motion.

The shape of the curve of force against the slide comes from some trigonometry, but that's unimportant. Here's a graph with simple lines to make the point.

http://i35.photobucket.com/albums/d199/harrygunner/misc/fbfps_effect_zps032698be.jpg

The X axis is distance the slide moves from left to right, the Y axis is force on the slide from the hammer. The reduction of energy of the slide is the area under the curve.

The bottom curve representing a 1911 with a FPS, shows how the slide loses more energy earlier in its rearward movement.

About recoil springs in 1911s - As far as the operation of a 1911, I don't see the recoil spring and slide looked at as a "springed mass" being important except for returning the slide to battery.

I propose that one should keep the recoil spring on the low side, chosen for reliable operation. That's because at the end of its backward motion and subsequent forward movement, the slide interacts with another independent system with its own time scale, the magazine. The top round in the magazine is a "springed mass". Why not give the magazine the time it needs to present a round to the forward moving slide. A stronger recoil spring reduces the time frame for the magazine to do that.

And the recoil spring does nothing for "delaying opening the breech face". I don't believe that phrase has a meaning for a 1911. The barrel link makes that a function of the distance the slide has moved to the rear. And for any realistic bullet weight, the bullet has left the barrel long before the link pulls the barrel down. A faster bullet causes the slide to move faster, but the net effect is the slide moves the same distance as a slower moving bullet when it exits.

harrygunner
June 16, 2013, 02:04 AM
In the spirit of 'Greg528iT' post, here's a photo of a now conventional FPS v.s. a flat one. The one on the left is in my 10mm, the rounded one to the right is in my .45 ACP.

http://i35.photobucket.com/albums/d199/harrygunner/misc/flat_vs_rounded_fps.jpg

1911Tuner
June 16, 2013, 04:52 AM
Harry...You've got it. Look at it like a lever and fulcrum. With a given load, you do the same work in lifting it. The location of the fulcrum determines how much force you have to exert in order to do the work.

The effect of the small radius/reduced advantage comes immediately...starting to fight the slide the instant it starts to move. Think of it like stabbing the brake pedal momentarily as you stomp the go pedal when the light turns green.

Greg...Your firing pin stop geometry is intended to increase the mechanical advantage in overcoming the hammer mass and mainspring load by placing contact high on the hammer...exactly the opposite of what the small radius accomplishes. I took Browning's small radius a little further and made it a little smaller in order to reduce the mechanical advantage, STI went in the opposite direction.

It's done to insure a strong cycle rearward with calibers or load levels that don't generate enough oomph to drive the slide. Your 9mm is one of those. I've done it myself with that .45 pistol that I set up for my daughter for use with powderpuff loads...around 600 fps with a 200-grain bullet.

As far as your issue with the disconnect, about all you can do is make sure the bottom of the stop is flush with the rail, and maybe do a light bevel.

1911Tuner
June 16, 2013, 04:55 AM
Here's a comparison. L-R:

1. The now standard 7/32nds radius.

2. Mine. The radius on this one is close to Browning's 5/64ths, but still just a tick smaller. Just a WAG, but probably around .070 inch. Like I said...I don't get trapped with minor detail unless I'm making one to restore an old pistol that was originally equipped with the 5/64ths radius...and since I don't presently have access to a machine shop with a Bridgeport and a full selection of radius cutting end mills, doing it by hand is an arduous process with the direction that my eyes have taken recently.

3. A stop that I found in an early 70B Combat Commander that checked out at roughly 5/32nds. I've never seen one like it in any Colt that I've looked at, and I have to assume that it was a glitch. The sharp corner at the top of the radiused portion suggests that the stop shifted in the
fixture.

By the way, I went back and checked the specs. I was wrong. The tolerance is +/- .003 inch on the radius and not the .005 that I quoted. Mea culpa.

http://i40.photobucket.com/albums/e243/1911Tuner/Stops2.jpg

NacsMXer
June 16, 2013, 12:42 PM
How critical is it to taper the face of the stop where the hammer meets it like seen here? Is it ok to leave a gap at the bottom as seen in the diagram at the right?

http://i900.photobucket.com/albums/ac210/Cuba1911/Firingpinhammargap_zps8c947636.jpg

http://i900.photobucket.com/albums/ac210/Cuba1911/TaperedFPS.jpg


Also, what is the easiest way to establish the radius on the bottom corner while keeping it absolutely straight? I don't want to fubar this thing and risk side loading the hammer pin. Drag it across a flat piece of sandpaper? Is there a better technique?

Thanks for your help.

1911Tuner
June 16, 2013, 12:55 PM
How critical is it to taper the face of the stop where the hammer meets it like seen here? Is it ok to leave a gap at the bottom as seen in the diagram at the right?

There's something familiar about that drawing...

Hmmm

I've never run into an ordnance spec pistol that showed any significant gap at the bottom. In every one that I've handled, the hammer starts to move as soon as the slide moves even the tiniest bit. If that gap is there, I'd suggest that there's a bug in the specs somewhere...likely in the hammer. Gotta watch those aftermarket hammers, lest ya go chasin' zebras.

Also, what is the easiest way to establish the radius on the bottom corner while keeping it absolutely straight?

Carefully. I use a file to break the corner at 45 degrees, then use a swiping motion on sandpaper laid flat on a piece of glass or flat stock to just start to roll the bevel. Many people just go with the bevel. Some don't do anything at all, and just leave it square.

NacsMXer
June 16, 2013, 01:19 PM
Thanks a lot 1911Tuner ;)

I just hope this Wilson stop plays well with my Harrison extreme service hammer.

Also regarding my 17/19 lb recoil/main spring combo: After I install the stop should I reduce the recoil spring and go back to a 16/19 lb setup?

I know a 23lb main spring is ideal for this setup, but i'd rather stay with the 19lb main spring.

1911Tuner
June 16, 2013, 01:55 PM
You could go all the way down to a 14 pound recoil spring.

The 19 pound mainspring is okay as long as it provides reliable ignition, but you won't get the full benefit from the small radius on the stop with one that light.

NacsMXer
June 16, 2013, 02:05 PM
Understood. Thanks again for your advice!

Greg528iT
June 16, 2013, 02:26 PM
I realized that it was to make it easier to rack the slide with the hammer up.

I do not think there is enough material to put a significant radius on the bottom. I'll check the disconnector, but I don't remember it standing overly proud relatively speaking and it's doing it's job QUITE well as is. Last range trip had some hand loads not going fully into battery (another story) but was glad the disconnect was there.

http://i1177.photobucket.com/albums/x349/jaggoett1/40572764-8e3f-48d2-ab65-c65f62cf0169_zpsd16d77f0.jpg (http://s1177.photobucket.com/user/jaggoett1/media/40572764-8e3f-48d2-ab65-c65f62cf0169_zpsd16d77f0.jpg.html)

I modded the picture a bit.. on the far left, is what was my initial concern. I think it'd have to be a very sharp edge and a very hard pin stop.

1911Tuner
June 16, 2013, 04:37 PM
Yeah. They didn't leave a lot on the bottom of that stop to work with. Can't wrap my head around the reason for that particular shape. There have been 9mm 1911 variants for years that had the standard 7/32nds radius, and they worked fine.

VetPsychWars
June 16, 2013, 08:08 PM
For my 10/18 Model of 1911, ordered their 1912 reproduction slide stop from Cylinder and Slide.

Any source of series 80 slide stop other than EGW (or at least some clue of how oversize it really is) would be appreciated. Gun is stainless but blue would be hard to spot.

As an aside, the Colt "Gold Cup" recoil spring on my M1911 makes the slide just feel like it's floating forward and I have no feeding issues. It's my hope that this new firing pin stop makes the slide just float backwards as well. At least it will make me feel better when the collectors scream YOU'RE GOING TO BREAK YOUR SLIDE! (stfu, thanks)

Tom

1911Tuner
June 16, 2013, 08:40 PM
For my 10/18 Model of 1911, ordered their 1912 reproduction slide stop from Cylinder and Slide.

Slide stop or firing pin stop?

Curious because I really like the old style slide stops, and if somebody is reproducing them...want.

VetPsychWars
June 16, 2013, 09:01 PM
Firing pin stop. Had a brain fart.

They have also the reproduction slide stop. I ordered one; I decided to not use it because the original has a .200 pin and the Cylinder and slide is .199.

But I hold it in reserve in case I ever break mine.

They made an entire series of 1912-style spare parts, including barrels.

Tom

Greg528iT
June 16, 2013, 10:10 PM
http://www.cylinder-slide.com/index.php?app=ccp0&ns=prodshow&ref=CS2309B&sid=0743l8wod143n18k0oh98w42wen7c0c6

No dimensions given, but looks close.

Why STI did it? I'm going with.. easiest slide racking and cause they can. Lots of things on STIs are just plain different. The plastic skeleton trigger- gone in less than 2 weeks.

Walkalong
June 16, 2013, 11:20 PM
I bought a Colt Series 80 Enhanced in .38 Super and added a 9MM barrel. The FPS was a sloppy fit and the extractor had a lot of play. For .38 Super it worked OK, but for light 9MM extraction/ejection was poor. I installed a new extractor and fit an EGW OS FPS and put a small radius on it. Now the extractor has no play and extraction/ejection is 100%. You can see where I rocked the FPS a hair *sigh*, but the wear is in the middle, so that is good. The radios is smaller than it looks in the pic.

Anyway, the point is that extraction/ejection is 100% with a #14 recoil spring and stock main spring shooting 124 Gr bullets at 1050ish FPS and the brass just piles up at my feet. Recoil is very nice.

http://www.cylinder-slide.com/index.php?app=ccp0&ns=prodshow&ref=CS2309B&sid=0743l8wod143n18k0oh98w42wen7c0c6
Nice, especially if it is a nice fit.
_

1911Tuner
June 17, 2013, 04:07 AM
Interesting, WA. I've installed a few for people with Supers, but have generally advised against using a radius that small on 9mm pistols because of short recoil concerns.

Sorta makes me wonder what was behind STI's thinking in their design.

Greg528iT
June 17, 2013, 11:02 AM
but have generally advised against using a radius that small on 9mm pistols because of short recoil concerns.

See the picture I posted.. the STI FPS, acts like a very large radius when acting on the hammer. It's the disconnector when assembling the slide that has more of a hiccup.

1911Tuner
June 17, 2013, 12:39 PM
I saw the picture and understand the problem with the disconnect. That's probably a spec issue, either with the shape of the disconnect or the center rail being too close to the top of the frame...or possibly both.

Without seeing the pistol, I can't advise you on what remedial action to take other than to establish a radius or a taper at the bottom the existing stop that extends into the center rail. It won't hurt anything and it won't be visible when the pistol is assembled.

hariph creek
June 17, 2013, 03:12 PM
This had been a great thread. Thanks to all for the great info.

When I started with 1911/10mm, the common recommendation was "put a (far to heavy) recoil spring in it."
This thread really, accurately, describes the application and inter-relation of the recoil spring, main spring and firing pin stop.

1911Tuner
June 17, 2013, 04:23 PM
When I started with 1911/10mm, the common recommendation was "put a (far to heavy) recoil spring in it."

Speaking of the Big Ten...

A few years back, top gun wrench Ned Christiansen conducted an experiment with one of his custom 10s, an EGW firing pin stop, a few recoil springs, and a pack of shock buffers.

Condensed version:

By observing the damage done to a shock buffer at a specified round count, he was able to closely duplicate the slide to frame impact with the stock 22-pound spring with an 18-pound spring by installing a stop with a square bottom in conjunction with a 25-pound mainspring.

He was able to drop recoil spring rate by a full four pounds, making the pistol more user friendly by reducing the amount of force needed to manually rack the slide and softening the felt recoil without sacrificing any slide to frame impact buffering provided by the 22-pound spring.

Peter M. Eick
June 17, 2013, 07:35 PM
My experience with the 10mm's in 1911 format guns is you can beat them up in reverse (too light of a spring) or you can beat them up going forward (too heavy of a spring).

A flat FPS helps a bunch but in the end you are going to beat it up in some way.

I am running 20 lb springs myself and slowly using up my buffers.

1911Tuner
June 18, 2013, 03:52 AM
Try Ned's recipe, Peter.

Greg528iT
June 18, 2013, 12:17 PM
I ordered a couple EGW oversized stops. I can always put the OEM unit back in. :)

the center rail being too close to the top of the frame
I'd have to measure it, read the drawings, do some math.... but basically, I'm NOT going to. The center rail does not contact the frame. I would say that the only way it could be too close was for it to ride / contact and rub. They do not. The disconnect works as it should. If the slide is out of battery by less than a 1/16" the trigger is disconnected. It might be smaller amount of out of battery, but I was on the range without a dial caliper.

I still need to look at the slope on the disconnector but I'm still betting it's the very sharp edge on the Pin Stop

Greg528iT
June 18, 2013, 12:38 PM
Thinking back and also confirming with my shooting partner.. slide out of battery was at times less than 1/32" .. We were looking pretty good, as they were his reloads and he has since ordered a new sizing die for his bullets.

1911Tuner
June 18, 2013, 12:47 PM
I'd have to measure it, read the drawings, do some math.... but basically, I'm NOT going to. The center rail does not contact the frame.

You'd have to detail strip the frame in order to measure it, and you'd need a set of ignition feeler gauges. The clearance should be .010 inch between the top of the frame and the bottom of the rail and the geometry of the disconnector head should be correct in order to create the camming effect.

The disconnect works as it should. If the slide is out of battery by less than a 1/16" the trigger is disconnected.

Good...but preventing firing out of battery isn't the function of the disconnect. If the pistol is far enough out of battery to be dangerous, the hammer can't reach the firing pin. You can't pull the trigger and fire the gun with the slide far enough out of battery to blow it up. It's mechanically impossible.

Greg528iT
June 18, 2013, 02:17 PM
Hate to side track this but
preventing firing out of battery isn't the function of the disconnect

What is it's function then? I thought that is what it was for.

At work so can't measure it.. but from memory, I'd say 0.010" is about what I have.
I really think the radius on the FPS, is what helps cam the connector down. Not it's function.. but the lack of a radius causes the hiccup. 2 radii work better together than 1 and 1 sharp edge.

VetPsychWars
June 18, 2013, 03:04 PM
Hate to side track this but


What is it's function then? I thought that is what it was for.

At work so can't measure it.. but from memory, I'd say 0.010" is about what I have.
I really think the radius on the FPS, is what helps cam the connector down. Not it's function.. but the lack of a radius causes the hiccup. 2 radii work better together than 1 and 1 sharp edge.
If I may... the disconnector is the thing that prevents the pistol from firing full auto. If you hold the trigger back during cycling, the disconnector "disconnects" it from the sear, so the sear resets and you actually have to let go of the trigger before the trigger reconnects to the sear again before you can fire the pistol again.

Trying to pull the trigger with the slide a little ways back is how you test that the disconnector isn't broken, but that's not why it's there.

Tom

Greg528iT
June 18, 2013, 03:08 PM
AH........

OK, I won't be removing it.. in case anyone is reading this. :)

1911Tuner
June 18, 2013, 03:15 PM
What is its function, then?

The disconnect's function is to bridge the gap between the trigger and the sear so the gun can fire, then to get out of the way and recreate the gap so the sear can reset. A side effect of that function is keeping the gun from firing with the slide out of battery, but that's all it is.

If I may... the disconnector is the thing that prevents the pistol from firing full auto.

Nope. It's a myth that filing the top of the disconnect flat will turn the 1911 into a machine gun. The hammer will fail to cock and ride the slide back down...but it won't burst-fire.

Walkalong
June 18, 2013, 10:35 PM
To fire full auto it would have to have a slight hesitation before falling (each time) to keep it from just following the slide back forward, ala an auto sear.

Not that a bang/bang can't happen, it can, but just exactly how I am not sure. Out of spec parts (As in more than one) I reckin'.

flightsimmer
June 18, 2013, 11:27 PM
Speaking of full auto! I bought a brand new Colt Gold Cup National Match years ago and took it to the range where I worked and loaded a full magazine of .45 auto into it and proceeded to take my first shot where upon it went full auto and emptied the whole magazine into the backstop and ceiling over my head, needless to say I never loaded a full mag in a new gun again.
I took it back to where I bought because they had a full time gunsmith and he fixed whatever was wrong with it but it was a long time before I ever loaded a full mag in it again.

1911Tuner
June 19, 2013, 12:56 AM
To fire full auto it would have to have a slight hesitation before falling (each time) to keep it from just following the slide back forward, ala an auto sear.

This.

The hammer has to hold at full cock and jar off as the slide goes home. Otherwise, the slide just lowers the hammer at slide velocity, and that's not enough.

VetPsychWars
June 24, 2013, 07:46 PM
Today I received and installed a Cylinder and Slide 1914 reproduction firing pin stop on my October 1918 Model of 1911. It required just a little taken off of one side because the slot in the extractor wasn't deep enough. Requires a bit of a push to get it on now but no hammer needed.

I hand-cycled the pistol a couple of times and I was incredulous... this tiny bit of added resistance caused an ordnance change? Really? How were these people cocking this gun that they couldn't do it with the small-radius stop?!

In any event... with that and the Gold Cup (aka 14lb) recoil spring, I'm eager to test fire. My purpose in making these changes is to be able to fire this pistol when I feel like it and have the slide not bang so much opening and closing. Slower is better!

I've also ordered the EGW stop (in stainless) and with any luck it won't be so oversize that I can't make it fit my Remington R1S using files and stones.

Tom

Fred_G
June 24, 2013, 10:39 PM
OK, put an EGW firing pin stop in my R1-S Remington 1911. Seems to require a bit more force to cycle the slide. Function checks work.

VetPsychWars
June 24, 2013, 10:59 PM
OK, put an EGW firing pin stop in my R1-S Remington 1911. Seems to require a bit more force to cycle the slide. Function checks work.
How much fitting did you need to do?

Fred_G
June 24, 2013, 11:21 PM
How much fitting did you need to do?
Not sure how to rate it. Say an hour or 2 with some files and a micrometer to get close, some fin sandpaper for the rounded edge.

Note: I am not a Gunsmith, just like to play around sometimes. I am curious how it will shoot.

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