Firing Pin Stop Geometry

[MikeRush]

Hello everyone,

I have been researching (including searches here) more about FPS shapes and angles for my single stack Kimber .45 and I think I may have made a mistake. I originally fitted an EGW square stop and only put a slight bevel on the bottom to "reduce recoil" and produce custom oval hammer pin holes.

I have shot other guns with an unknown (to me, a Wilson CQB comes to mind) radius and I think that in addition to adding wear to my frame I am making it more difficult to track the sights.

I am currently running a 16 lb recoil spring and a 19 lb mainspring, planning on dropping to a 14 lb recoil spring... if this is too 1911 specific maybe I could get the thread moved but I am looking more into what kind of radius shapes and how they affect perceived recoil.

I have been looking online, one option seems to be the brazos stop that looks (to me) like a larger bevel that is more flat relative to the stop and begins well below the firing pin hole. I have seen references to things like an "exponential" radius or a radius that runs all the way up to the FP hole.

Would anyone be willing to share insight with a willing to learn newbie? I want an idea of what radius I might try (besides the factory radius)that I can settle down with and get used to so I can have more confidence in the gun and place the blame for poor performance where it belongs (on me).

Any images or ideas where to look? I have searched here but perhaps my terminology is incorrect.

Thanks in advance for any words of wisdom!

[Roadrider18]

You didn't mention which Kimber model you own. I will assume it is a 5" 1911.

Oval hammer pin holes because your slide is accelerating too fast aft? I have seen oval pin holes because they were not accurately positioned when the receiver was manufactured, but, not due to the slide's momentum. I am not saying it can't happen, I simply haven't seen such.

A 1/16" or slightly smaller radius will work fine.

A small radius will decrease the slide's mechanical advantage in overcoming the hammer/main spring. Further, the slower the slide is going as it reaches it aft position the less battering on the impact area of the receiver.

The recoil spring has nothing to do with decelerating the slide's aft movement. It is for accelerating the slide forward into battery.

I am not in agreement with your use of a 19# main spring unless this is strictly a game gun. I would use a 23# main spring. If it is a game gun, you can try down to a 17# mainspring. I wouldn't go much lower.

A 1/16" radius on the FPS with a 23# hammer spring and a 16# recoil spring offers a pretty good sweet spot for a Kimber 5" 45ACP 1911.

If you do swap out the recoil spring, I wouldn't go with less than 14#.

Edited December 7, 2011 by Roadrider18

[Aircooled6racer]

Hello: The firing pin stop can effect more than just the feel of racking the slide. It also depends on the hammer you are using etc. If the radius is higher up it will let the hammer get more leverage and should have less pressure on the pin. Using lighter weight springs 14lb recoil and 17 mainspring works well. I would buy a couple of firing pin stops and see which one offers the better/lighter racking of the slide. I actually made a fixture to machine the firing pin stops the way I like them. I installed one of the EGW stops in two different pistols and the felt completely different. The one was very hard to rack and the other was just fine. Thanks, Eric

[outerlimits]

Jim boland did some wierd shit wirh these. He built a steel gun where the angle of the stop was so exagerated that it actually cut into the disconnector notch!

[BoyGlock]

Jim boland did some wierd shit wirh these. He built a steel gun where the angle of the stop was so exagerated that it actually cut into the disconnector notch!

Ive seen a similar made gun by a local smith. The gun was ruined as it affected the disconnect function. I wonder what it was trying to accomplish.

[want2race]

Jim boland did some wierd shit wirh these. He built a steel gun where the angle of the stop was so exagerated that it actually cut into the disconnector notch!

Ive seen a similar made gun by a local smith. The gun was ruined as it affected the disconnect function. I wonder what it was trying to accomplish.

Wouldn't it just need a new slide?

To the OP:

Get 4 slide stops on hand. Cut each one different, very small radius, standard radius, large radius (from base to FP hole), and cut one with a flat "wedge" angle. Test each one with your spring combination and ammo. Use a timer and do something like 5 yard bill drills on the clock. Try to run the same speed (2-2.5 seconds) with each change and just watch the sights and record the accuracy of each run. I shot a wedge for a while, then a small radius, then large. Now I think I'me back to a standard radius. In the end, all mouse traps catch mice.

Happy testing

[MikeRush]

Thanks everyone for the replies so far! The gun is question is a 5 inch Custom 2.

As far as the square stop I am looking to try something different- While I understand how it can slow down the rate of initial slide acceleration I dont think I need it for my 200 gr LSWC loads. They are loaded down to just make major. I am also coming to the realization that this gun for me will be a "game gun", due to the series 2 safety and MIM parts+ sometimes questional willingness to feed properly. I haven't had a single light primer strike with the 19 lb mainspring. Unless the primer is backwards a chambered round will go bang.

I have the factory radius stop that I swapped out because it didn't hold the extractor firmly enough and my fitted square stop. I think I will pick up some more stops and run a comparison as suggested. I would like to find one that is acceptable and settle on it.

Again if anyone has pictures of their stop profiles I would love to see them... a google search hasn't shown me that much because I dont think this is a common thing for people to take pictures of. Most are either square or factory radius.

Thanks again,

Mike

[BoyGlock]

Jim boland did some wierd shit wirh these. He built a steel gun where the angle of the stop was so exagerated that it actually cut into the disconnector notch!

Ive seen a similar made gun by a local smith. The gun was ruined as it affected the disconnect function. I wonder what it was trying to accomplish.

Wouldn't it just need a new slide?

It did

[HI5-O]

I like the Brazos slightly oversize FP stop on my open gun. Works well with the AFTEC extractor.

[MikeRush]

Thanks to everyone for the recommendations I am ordering up a brazos oversize stop to test. I re-contoured the square stop and I am loving it, I will post pictures later but it is much easier to charge the pistol and on my timer app the splits dropped a bit. It seems much easier to track the sights now, I shot a local steel match on Saturday and annihilated my previous best time on the match by 13 seconds. Quite happy with it!