Small radius firing pin stop form and function?

[prs]

I am not a total green horn, but not a whole lot of exposure to 1911 pistols; got my first one just a year or two back and a second one this past summer. A recent thread about different magazine types somehow got me to thinking about "small radius firing pin stops". Not too long back that part was discussed and tweaked my attention, but I forgot about it without understanding the concept. Anyway, I have looked at some posts that I was directed toward and maybe it is starting to soak in. Old hands, jump in here and lay it on the table for us less informed. Where on the firing pin stop is this "small radius"? I see some makers saying all the corners are "radiused" to prevent cracking, but I envisioned something else.

84387

84389

If the above two images pirated from Wilson Combat's listing on Midway USA appear, where on the pics would one look to see the "small radius", if present at all? I looked at the EW site and did not really see a stop called "small radius". The top pic shows the bottom edge having been milled or rounded over a bit. The left hand corner of both are rounded a bit rather then being square cut, is that it?

I understand the small radius firing pin stop is nothing new, but the way JMB did it; right? That part of the idea is to start with an over sized part and carefully fit it to be really snug rather that "slip right in" or sloppy fit; both side to side and front to back and also in relation to contact with extractor and hammer face.

I appreciate the enlightenment!

prs

[Paul105]

Here are a couple of links (from EGWs website ) that discuss the over sized, squared/small radius firing pin stop:

http://forum.m1911.org/showthread.php?t=13060

http://forums.1911forum.com/showthread.php?t=164678&highlight=egw+firing+pin+stop

EGWs website
www.egwguns.com/firing-pin-stops/oversized-series-80-firing-pin-stop/


Paul

[35remington]

The small radius part is on the bottom front of the stop, the part that faces the hammer. The tighter fit is not something that was a production item, but rather a benefit of hand fitting the part to have close tolerances if it is done yourself or by a gunsmith. The hand fit was not part of 1911 production. Don't get the idea that small radius stops were originally hand fitted for extra "tightness" when the 1911 was introduced because they were not.

The small radius stop was a feature of 1911 production for about 13 years after it was introduced. Instead of a generous rounded bevel it's just a tiny curve or rounding of the bottom edge. A much smaller rounding, in other words. Idea is to reduce the leverage the slide has on the hammer and make it hard to cock.

The benefit is it robs the slide of some momentum and makes the slide hit the frame less hard. This is a benefit a "shock buff" and heavier spring provides without the drawbacks inherent to using a shock buff and a heavy spring. In other words, a better way to do it.

This reduced impact of slide to frame makes the gun more reliable as it reduces inertial misfeeding of the last rounds in the magazine. Heavier springs and shock buffs make the 1911 less reliable. Which to choose should be a no brainer.

A tight fit of the stop reduces "clocking" of the extractor (turning) and makes ejection more reliable as well, as the ejector has the correct presentation to the case rim and cannot turn or deviate from the correct angle. The EGW supplied part comes square and you must form the radius yourself with a stone or file. This allows some room for experimentation as to the radius size.

"The top pic shows the bottom edge having been milled or rounded over a bit." That rounded edge on the bottom front of the stop is the radius.

Your top picture shows a stop with a standard 7/32nd's radius as found on all 1911's as currently produced. It was not standard when the pistol was introduced, but rather a change the Army mandated in the 20's. See the radius at the bottom of the stop? (The lighter area shows the curve in the picture). The second picture is of a stop that is square with no radius at all. The radius must be formed with that file or stone and is done by the user or gunsmith.

A full size pistol can get away with the smallest radius, as will one set up for heavier loads. Bullseye pistols shooting light loads have little reason to have a small radius stop fitted. The slide doesn't smack the frame that hard and its addition may make the gun malfunction as the slide will no longer reach full travel with loads that worked with the regular firing pin stop of 7/32nds radius.

[prs]

Thank you Paul105. I still have some reading to do.

35 Remmington; I appreciate that excellently scribed essay. Now I understand. I removed and examined my two OE Ruger samples; one standard, the other Commander. They are essentially identical with the modern large radius. The fit in my Commander was close, yet still loose enough to free fall out of the slide. The fit in my standard size pistol is snug enough to not fall out, but easy to install. Good information!

PigeonRoost Slim

[btroj]

The small radius stop makes a big difference in felt recoil for me. I find it tames brass throwing a bit too.

Easy to fit, mine is a bit sloppy but it works!

[MtGun44]

I made up a small radius stop a while back. Liked the slightly different feel and more consistent
ejection distance and direction so I kept it in.

Bill

[prs]

I ordered a pair to experiment with. Experimenting is one of two areas in this life-long gun quest that I find most enjoyable. Casting is a wash; it is interesting and fun to a point, but there is quite a bit of drudgery to temper those jollies. Shooting; well anything that goes BANG and has an observable consequence is Joy to me. Experimenting and seeing what goes wrong/right or indifferent, that is also a thing over which to wax poetic.

Thanks to you all for the education!

prs

[Paul105]

The original John Browning design incorporated a 16 lb slide/recoil spring and a 23 lb main/hammer spring along with the non radiused firing pin stop.

I should have mentioned this before, but thought you would come across on one of the above posted links. The guy that posts as 1911tuner is a wealth of information on the 1911 -- you can google him and get a lot of his stuff.

FWIW,

Paul

[prs]

I did read about that within the material you posted.

prs

[MtGun44]

I think you mean "small radius" stop not "non-radius" stop. As I would understand
the term, a "non-radius stop" would have a perfectly square bottom edge, not good
for wear on the stop and hammer. Plus the prints I have for the original 1911 show
a small radius, not square bottom on the firing pin stop.

Bill

[prs]

I have received two over sized firing pin stops without any relief of the hammer contact area. These are the EGW parts. I compared to the stock stop in my Ruger SR1911 and the over sizing is evident in the thickness of the metal, the width, the height, and the thickness of the dado shoulders. But, not a lot of hand milling/polishing to do. The new parts are just barely too large to fit as is with the extractor out. I will fit it carefully when I find one of those rare round tuits.

prs

[gray wolf]

The original John Browning design incorporated a 16 lb slide/recoil spring and a 23 lb main/hammer spring along with the non radiused firing pin stop.
That is not entirely true, the FPS did have a slight bevel to it. Also the original recoil spring was #14 to 15 #
14.5 comes to mind. The 16# spring came latter and has since been adopted as standard.

[prs]

I fitted the stop this afternoon. Came out really good. Nice and snug in the frame and tight to the extractor. I hope to function test tomorrow.

The explanations and hints provided by you folks above are greatly appreciated!

prs

[MtGun44]

What bottom rear radius did you add?

Bill

[btroj]

Not much I hope. I barely broke the edge on mine.

[prs]

Remember, I purchased two. This first one I rolled the bottom rearward hammer contact edge over to the extent that the radius occupies 1/3 of the thickness of the metal. That is probably more than btoj was hoping, but there is method to my madness and consider that my OE stop covers about 9/10s of the thickness. I fashioned this one with lightly charged 200gr SWC ammo in mind. I did keep the fit to the frame and ejector snug to where it takes a good press of the thumb to insert and a little pry to remove, no slop at all.

How did it work? I was pleasantly surprised! Its not that I didn't believe you guys, but I expected a more subtle result. I shoot one handed, either left or right, but just one hand on the pistol. The reduction in muzzle lift was remarkable. Recovering the sight picture far quicker, more accurate.

After the shooting session I stripped and cleaned the gun looking closely for signs of uneven contact with hanner face, all good. So I polished the stop and reblued its finish. Now, the second one might be set-up with an even smaller roll-over to suit heavier charges and 230gr boolits, or find its place in my Commander.

Thanks again for the education.

prs

[btroj]

Mine is also an EGW oversized stop. Mine has the bottom edge barely broke , a few strokes with a fine stone. Works like a charm. Changed the entire feel of recoil, keeps brass closer too.

[prs]

Any indication your very small stop is gaulling the hammer face?

prs

[btroj]

None at all. My stainless Gold Cup has many thousand rounds thru it and the hammer looks no different than it did before.

[prs]

btoj, following your lead I decided to fit the second square oversized stop to the same gun with a very small stop. I used 220 3M wet sand paper to carefully break and round over the edge. Followed with 440 then 600 and even 1000 for a precise mirror finish. It is about 1/16" rad or a tad under conparing to drill rod as a reference. BTW, I compared my previous completed stop to drill rod and closest match is at or just under 1/8", but not a true rad as I relieved the approach and exit a bit. The one I did today, I kept tight enough to require light tapping to install and remove and it really nails the extractor to the frame. Will take to range with full power 230 Lyman hardball clones and light 200 SWC ammo, can always polish more, if needed.

Thanks to Y'all for explanations and suggestions.

prs

[prs]

I put 125 rounds through my standard sized SR1911 today. 230gr Lee TC and 230 Lyman RN E
each with full charges, plus the 200gr Lee 68 clone and Lyman 460 SWC were run through traditional magazines, Wilson Combat magazines, and an early release style from forgotten maker.

Nary a hiccup. Similar feel as reported with the slightly more radiused example above. I will next see if that other example has anything to offer for my Commander.


ps: The Commander did not "like" the smaller radius, almost 20% failure to fully feed. Fitting the ejector side was required, so that stop is now a resident of my scrap box. Good learning experience though.

prs