EGW Firing Pin Stop


August 11, 2006, 12:50 PM
We had a pretty good talk about the small radius FPS in the 1911 the other day and I was pretty skeptical about some of the claims. It was an interesting idea though, both from a historical and a mechanical perspective.
Tuner is tops on the 1911 and has made some very good posts on the care and feeding of this king of pistols. Despite my doubts from a mechanical point of view, I got a couple of the stops and tested one today.
The stop itself appears well made and it fit up nicely with a minimum of fuss. I left it almost square on the bottom with a very small radius to get the most effect.

Results? I can't tell the difference. I fired 150 rounds with the small radius and then switched back to the standard radius for 50 more rounds. Operation was 100% and the ejection patterns and recoil seemed the same. Manual racking of the slide with the hammer down was somewhat more difficult with the small radius FPS.

Why no change in operation? I don't know,but plan to fire this mod in some other pistols and try some other springs and loads and see if anything shakes out.

One thing that struck me is that just about every FPS I've looked at has a hammer impact line just above the firing pin hole. It may be that the hammer is slapped back from this point and the bottom radius doesn't have much to do with it.
In any case you will end up with a FPS that will most likely fit much better than the factory version.

YMMV, and it would be interesting to hear from those who have switched back and forth with the small FPS radius.

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August 11, 2006, 02:45 PM
I dunno, jungle...Maybe you're not payin' attention to it. Or...maybe you've made up your mind that ya don't wanna believe it...but you seem to be about the only one who's tried it and doesn't notice SOME change. Did you install a fresh mainspring?

Here's one of the latest, from a guy who was a little skeptical too.

Old Fuff
August 11, 2006, 03:22 PM

The impact line on the firing pin stop above the firing pin is caused by the hammer when it falls. If you look carefully you will also see rub marks on the face of the hammer caused by the firing pin stop as it pushes the hammer backwards as the slide is retracted. If you don't see this clearly coat the hammer face with some layout dye. Also the greater the F.P.S. radius is, the higher the rub marks on the hammer face will be. You are working with a lever here, and the further away the F.P.S's impact on the hammer face from the center of the hammer pin, the easier it will be to push back the hammer.

August 11, 2006, 03:48 PM
Thanks Old Fuff, I understand all that. My question is if that line above the firing pin is the contact point at rest, is it not plausible that the slide is slapping the hammer back from that initial point of contact?

Some seem to think the hammer is in continuous contact with the slide during recoil, but it seems this is not the case. It is obviously the case in a manual rack.

Interestingly enough the rub marks on the hammer didn't seem to change at all. But of course, this was 200 rounds vs. a few thousand, although the hammer impact line appeared on the FPS almost immediately.

August 11, 2006, 05:50 PM
I have a couple laying around with different cuts on them, and another new one with no cut at all. I picked up a new-to-me single stack in 45 the other day, I think I will play with it instead of the competition gun I was talking about in the thread the other day.

I definately notice a difference, both in feel and by what the front sight does in recoil. I see less difference than I feel, but it is definately different. I run springs a little lighter than most, usually a 14 pound recoil and a 19 pound mainspring in a hardball gun.

IF I can find my singlestack stash of parts I have mainsprings and recoil springs of just about every weight made, so I can play with that too.

I am surprised that you didn't notice a difference.

August 11, 2006, 07:15 PM
Fuff...I'm gonna try one..more...time.

>>My question is if that line above the firing pin is the contact point at rest, is it not plausible that the slide is slapping the hammer back from that initial point of contact?<<

Nope. If you have Kuhnhausen's Volume 2, look at the top of page 42, Figure 4. You'll notice that the hammer is in contact with the stop not just at the top, but all the way down to the point that the radius creates clearance.
Remember that the hammer doesn't move in a straight line, but rotates around the pin. As soon as the slide budges, contact at the top is broken, and it starts to move farther down the hammer...closer to the pivot point. By the time the hammer has rotated a degree or so, all contact is on the small radius. When the 7/32nds radius is in place, the hammer is allowed to move through a longer arc...maybe 5 or 6 degrees...before contact is on the radius. By that time, the slide is moving faster. When the slide is moving faster, it overcomes resistance more efficiently. Objects in motion, etc.etc.

>>Some seem to think the hammer is in continuous contact with the slide during recoil, but it seems this is not the case. It is obviously the case in a manual rack.<<

You're correct here. During live cycling, the hammer is in contact with the stop for only a short time before being slammed rearward to full cock. Nothing accelerates instantaenously, though. There are some fairly high forces fighting to maintain contact between the hammer and FP stop, and the faster the slide moves, the harder these forces try to maintain that contact. Once the hammer loses contact with the firing pin stop, the influence of the bottom radius is over, no matter what the size of the radius is.

The smaller radius affects this in three ways. First is that its influence starts earlier in the slide's travel, and maintains contact for a couple of degrees longer. The second is that by moving the point of contact farther down on the hammer, it decreases the mechanical advantage that the slide has in overcoming the mainspring's resistance. By starting earlier and maintaining contact longer...and by decreasing the mechanical advantage in cocking the hammer, the slide is more delayed during its initial movement...when inertial and other resistive forces are harder to overcome. Objects at rest, etc. etc.

The final effect probably has the least effect, but is still a player. The smaller the radius, the higher the frictional resistance between the stop and its contact point with the hammer. Why? Because the load is concentrated on a smaller surface area and because it's harder to push something around a corner than around a curve.

Have I left anything out, Fuff?

August 11, 2006, 07:29 PM
Tuner, Good explanation, although quite a few of the KII illustrations do not accurately depict the exact interplay between parts. In most cases I have seen there is a single point of hammer contact at the FPS, and it lies above the firing pin when the hammer is at rest. I understand the relationship in a hand rack and how the radius slides up the face of the hammer, and how the point of hammer contact moves down the face of the FPS.
In the dynamic situation of the slide and hammer I am reminded of two steel balls -hold one still and smack it while it rests against another, the free part moves and the fixed part doesn't(or very little).
Like I said, I'll keep playing with it in combination with some other springs. I just may be insensitive to such a small change. Hell, maybe I'm insensitive to a large change. Thanks again.

August 11, 2006, 08:06 PM

For the record...I've never touted this thing as a "Recoil Reduction Device" though that's one of the side-effects...and that will vary from gun to gun and shooter to shooter. High firm grip. You won't notice as much least not a readily apparent change. It may be that you notice that your hand doesn't tire as quickly, or when you realize that you're getting back on target faster after recoil. Those two things are what hit me. I felt relatively little change in felt recoil, but other the two mentioned above... gradually became more apparent. Suspecting why, I ordered a pack of shock buffs and put it to the test. It was...revealing...and may provide your definitive test.

You'll feel the most difference shooting one-handed, bullseye style, with a light or medium grip. It also depends on the mainspring's load and condition. Light or much-used mainspring...You won't feel it as much as with a standard or fresh spring.

The main advantage....and the one that I reference that it allows the use of a lighter recoil spring without sacrificing any impact buffering...or it adds to the buffering effect without the disadvantages of using a heavier recoil spring.

August 11, 2006, 08:12 PM
I do use a high firm grip, so you may have nailed it there. I'll keep using it and try the spring variations. Have a good weekend.

August 11, 2006, 11:54 PM
The small radius FPS has changed the shooting characteristics of several of the 1911ís that I regularly shoot. These individuals all have functioned normally before the commonly available FPS is switched out for a small radius one. I notice the difference immediately after the FPS is installed and individuals approaching 1000 rounds have exhibited no ill effects. The benefits which I have personally observed and experienced are: 1) reduced perceived recoil, 2) reduced muzzle flip, 3) quicker follow-up shot, 4) increased accuracy of follow-up shots. These are actual observed phenomena after firing +/- 2500 rounds in more than one 1911 and not some momentarily attractive theory or argument to flog ad nauseam. Now this is the standard mod to all keepers. Ones that don't make the grade get their standard larger radius firing pin stop replaced before going on their merry way.

August 12, 2006, 09:03 PM
2XS is busy embarrasin' the tupperware crowd with his Glockspankin' Norinco these days. Showoff! :D

August 13, 2006, 08:33 PM
That ol' pistol? It's just a clone, and a Chinese one at that. Not even a Colt. Really only a pile of miscellaneous parts ....:cool: (one of which happens to be a small radius FPS)

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