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Old June 11, 2013, 08:17 PM   #1
MCMXI
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Small radius firing pin stop for 1911s

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 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.



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Old June 12, 2013, 05:10 AM   #2
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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.
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Old June 12, 2013, 06:45 AM   #3
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25 people showing up to tell you that it's all in your mind in 3...2...1...



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.
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Old June 12, 2013, 10:05 AM   #4
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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?
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Old June 12, 2013, 12:47 PM   #5
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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
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Old June 12, 2013, 01:38 PM   #6
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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.
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Old June 12, 2013, 01:44 PM   #7
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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
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Old June 12, 2013, 01:46 PM   #8
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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.
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Old June 12, 2013, 02:00 PM   #9
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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.
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Old June 12, 2013, 02:35 PM   #10
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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.

Last edited by huntershooter; June 12, 2013 at 02:48 PM.
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Old June 12, 2013, 04:04 PM   #11
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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
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Old June 12, 2013, 04:14 PM   #12
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Quote:
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.

Quote:
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.

Quote:
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.
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Old June 12, 2013, 11:10 PM   #13
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Quote:
Originally Posted by 1911Tuner View Post
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.
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Old June 13, 2013, 05:31 AM   #14
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Quote:
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.
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Old June 13, 2013, 10:07 AM   #15
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Quote:
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.
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Old June 13, 2013, 10:15 AM   #16
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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..
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Old June 13, 2013, 10:15 AM   #17
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Quote:
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.
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Old June 13, 2013, 10:30 AM   #18
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Quote:
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.
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Old June 13, 2013, 10:33 AM   #19
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Quote:
Originally Posted by jmorris View Post
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
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Old June 13, 2013, 11:08 AM   #20
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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.
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Old June 13, 2013, 11:55 AM   #21
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Quote:
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.
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Old June 13, 2013, 12:30 PM   #22
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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.
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Old June 13, 2013, 12:41 PM   #23
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Quote:
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.

Quote:
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.
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Old June 13, 2013, 01:24 PM   #24
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Quote:
That lets you use more recoil spring
This is a polar opposite to your normal 1911 protocol, is it not?
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Old June 13, 2013, 01:41 PM   #25
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Jim wrote:

Quote:
That lets you use more recoil spring
And Greg wondered:


Quote:
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.
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