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Old June 16, 2013, 01:04 AM   #51
harrygunner
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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.

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Old June 16, 2013, 03:52 AM   #52
1911Tuner
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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.
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Old June 16, 2013, 03:55 AM   #53
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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.

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Old June 16, 2013, 11:42 AM   #54
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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?






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.
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Old June 16, 2013, 11:55 AM   #55
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Quote:
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.

Quote:
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.
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Old June 16, 2013, 12:19 PM   #56
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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.
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Old June 16, 2013, 12:55 PM   #57
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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.
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Old June 16, 2013, 01:05 PM   #58
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Understood. Thanks again for your advice!
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Old June 16, 2013, 01:26 PM   #59
Greg528iT
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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.



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.
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Old June 16, 2013, 03:37 PM   #60
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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.
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Old June 16, 2013, 07:08 PM   #61
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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
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Old June 16, 2013, 07:40 PM   #62
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Quote:
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.
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Old June 16, 2013, 08:01 PM   #63
VetPsychWars
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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
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Old June 16, 2013, 09:10 PM   #64
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http://www.cylinder-slide.com/index....h98w42wen7c0c6

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.
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Old June 16, 2013, 10:20 PM   #65
Walkalong
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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.

Nice, especially if it is a nice fit.
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Old June 17, 2013, 03:07 AM   #66
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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.
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Old June 17, 2013, 10:02 AM   #67
Greg528iT
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Quote:
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.
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Old June 17, 2013, 11:39 AM   #68
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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.
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Old June 17, 2013, 02:12 PM   #69
hariph creek
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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.
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Old June 17, 2013, 03:23 PM   #70
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Quote:
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.
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Old June 17, 2013, 06:35 PM   #71
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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.
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Old June 18, 2013, 02:52 AM   #72
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Try Ned's recipe, Peter.
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Old June 18, 2013, 11:17 AM   #73
Greg528iT
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I ordered a couple EGW oversized stops. I can always put the OEM unit back in.

Quote:
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
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Old June 18, 2013, 11:38 AM   #74
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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.
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Old June 18, 2013, 11:47 AM   #75
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Quote:
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.

Quote:
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.
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