Small Radius FPS on 3 inch Kimber

[BillC]

I was going to add this in response to Banger19s post
but I’ve got a few questions of my own.
Sorry if this is a little long winded.

I installed the EGW firing pin stop in my TRP last week.
First I removed the original FPS and extractor from the
side and measured them. I was pleased that the original
FPS was fairly snug.

Rather than removing material from each side of the
rear face(s) (looking at it installed) of the FPS, I chose
to reduce the overall thickness by removing material
form the front (slide-to-FPS surface) face. This was done
in order to preserve the factory cut and finish. I didn’t
think I could duplicate that with a file by hand. I did this part
with 220 emery cloth over a granite lapping bock.
The piece of glass idea would work fine too.
Fitting the FPS to the extractor first is he only way to go IMHO.
Then I reduced the width with a 6” Nicholson mill [bast*rd]
until I got pretty close. You can always take away but you can’t add.
I did the finish cut/polish with a
Hard Arkansas Stone and deburred those corners.
This works great if you don’t have anything else to do for a while.
The fit is tighter that stock. It can be installed barehanded
but not removed barehanded.

I made a “jig” of sorts to cut the bevel.
I wanted to start small so it didn’t take long. I used the
stone to do that. I have a very small 16th radius bevel.
Its much harder to pull that slide back.

At the range, the first thing I noticed is that it no longer ejects my
powder puff loads. I had some hotter ball ammo
with me and, I’ll have to say, there is less muzzle
flip now than before.

Next I replaced the FPS in my Kimber Ultra CDP.
I used a -very small- radius on this as well.
The difference is more noticeable on the 3” Kimber
than the TRP. To date, the Kimber Ultra has given me less problems than the TRP.
Although I don’t beat the CDP like I do the TRP.

For 15 bucks and the fun of doing it, I’m happy with the EGW firing pin stops.
I’ll perform that upgrade to all my 1911’s. :)

My question(s) is this:
What problems will the small radius on the FPS cause on a 3 inch gun, if any?
So far it functions fine. Am I causing any damage I haven’t seen yet?
Does the small radius over stress the hammer pin?

[1911Tuner]

What problems will the small radius on the FPS cause on a 3 inch gun, if any?

Depends. The lighter slides and stout spring rates may stack up and cause short-cycling...or not. You'll have to experiment. No problems in my Colt Officer's Model with the .078 radius. (5/64ths)

Am I causing any damage I haven’t seen yet?

No more than normal wear. I've had the small radius stop in my brace of beaters for many tens of thousands of rounds each. No problems so far.

Does the small radius over stress the hammer pin?

A little...but unless the pins are soft...as in made of leaded/sulfured steel to make it more readily machinable...it shouldn't be a problem. Even if they are made of the wrong stuff...it won't likely cause a problem for a good many years of use.

Although John Browning didn't have an engineering degree...and probably not even the equivalent of today's HS diploma...he was a keen stress guesser. The small radius stop...5/64ths...was as per original design. The pins were hard, but the frames of the day were soft. If a problem wer going to show, it would have shown in the egg-shaping and wallowing of those holes.

[73Driver]

The fit is tighter that stock. It can be installed barehanded
but not removed barehanded.



This small radius FPS is my first attempt to do any work on my guns and I am triple checking before I head out to the range.

I used the same basic idea as BillC by removing the extra FPS from the face between the FPS and the slide. I used the glass surface and 600 grit sandpaper, boy did that take a while but is it SMOOTH! My fit came out the other way, it can be hand fit in and if you turn the slide upside down the FPS will slip out. My question is: is that too loose. There is no side to side slop, it doesn't wiggle when installed, the hole is directly over the FP, it just slides out by gravity.

Thanks for any input.

[tightgroups]

If your getting all the benefits from the OSFPS and experiencing no clocking or extracting problems you should be good to go. On the other hand if it plum bothers you, order up another and be a little more careful to get a tighter fit the second time around.

[1911Tuner]

If your getting all the benefits from the OSFPS and experiencing no clocking or extracting problems you should be good to go.

Bingo. The only advantage of the stop being press-fit is that it reduces the chances of the stop falling out of position and tying up the gun when the slide smacks the frame and the firing pin spring is badly worn/weak...or too short...to reset the firing pin in time. A backup for poor maintenence and nothing more. A fresh firing pin spring that's within spec about every 5,000 rounds will prevent that nicely.

[BillC]

I about half expected the Kimber to short-cycle with that small of a bevel. Its got stock springs in it and used to eject brass relatively far, now only three to four feet. I tried some of my lighter target loads, 200gr. SWC/4.8gr. Bullseye. It worked fine but only threw brass about a foot.
My original plan was to start with the small bevel, test fire, and increase the bevel incrementally until it functioned properly. By chance, it seems like I got it right on the first go ‘rounds. After another few hundred rounds or so I’ll know for sure.

37Driver, if noting wiggles, I’d say your OK. You may want to think about replacing your firing pin spring – or not. I’ve contemplated a way to tighten a FPS that is a little loose, depending on where it’s loose at. Knurl it. Lay the FPS face up on something solid and flat, take a good sharp center punch and strike four places, in a square/rectangular pattern keeping away from vertical of the firing pin hole and inside of the FPS “flanges”. This would raise some material up and you’d be able to refinish to fit.
That’s my THEORY. I DON’T KNOW FOR SURE THAT THIS WOULD WORK. If a guy didn’t have a extra FPS it might be worth a try. Like 1911Tuner and tightgroups suggested, its probably fine. I go by what those guys say.

Thanks for the feedback all.

[73Driver]

Thanks for the input, I have replaced the recoil spring, main spring and firing pin spring with Wolff springs. 16# recoil, 23# main and I think the Wolff set comes with a "heavy duty" firing pin spring. I knew enough to buy two FPS at the same time, just in case. ;) I'll try the current installation and if any problems popup, I'll start filing again. Sam