Lessening recoil with Reduced Radius Firing Pin Stop for 1911
A few years back, I addressed a problem that a guy on on a gun forum was having with an unstable extractor. It was clocking…or rotating…and causing him a few issues. The cure was to closely fit an oversized firing pin stop, and the only one that I had was an EGW part that comes with out a radius on the bottom corner. A few days after, he posted on the board that there was an amazing reduction in recoil…and the result was a discussion/argument that lives to this day.
It all started nearly 40 years ago when I noticed the difference in that radius on some older pistols. Curious…I swapped an original stop that I found at a gun show into a stock WW2 Ithaca and fired the gun back to back with the two stops. I did notice that the gun had a different ‘feel” and that started my scrounging of the junk parts bins at the shows. It netted me a few stops, but they eventually dried up, and I was forced to make my own from flat stock.
I understood the physics, but I never saw the stops with the 5/64ths radius as a recoil reduction device…because there wasn’t really enough difference to write home about. I just liked the way the gun felt with the slight added slide delay. The original specs as set forth by John Browning and the Dream Team called for that radius to be .078, or 5/64ths inch. In January 1918, in response to complaints of the slide being too difficult to hand-cycle with the hammer down…the army ordnance board approved a change to the present-day 7/32nds radius.
Then, along comes George Smith’s oversized stop with no radius, which also allowed me to fit it to the slide and the extractor…which, like my home cobbled parts, not only let me choose a smaller radius than Browning’s…but it also let me fit the stop and completely stabilize the extractor for more consistent ejection patterns. I didn’t have to make’em one at a time any more. Win-Win.
While I was aware that it did in fact have an effect on felt recoil, that was never the reason that I used it…and I took it one step further when George Smith started offering them…by going even smaller on the radius. I never worked for an exact number…but it’s somewhere around 1/16th inch.
So…If not for recoil reduction…then why?
Simple. My whole point with the 1911 is troubleshooting and correcting functional issues. Reliability is my focus. The small radius stop is a reliability tweak. No more and no less. If it didn’t enhance reliability, I wouldn’t waste my time. The fact that it stabilizes the extractor and makes ejection more consistent is a bonus. Recoil? pfft. The 1911 ain’t that hard to handle.
How does it enhance reliability? By slowing the slide in recoil, thus reducing not only the recoil spring’s backward shove on the frame…it reduces the level of whack when the slide hits the impact abutment…which is what causes muzzle flip…what we recognize as recoil.
When the race guns appeared, it seems that everybody wanted a 1911 pistol that ran faster than the Word of God. They started overspringing the slides for a faster return to battery and the like…because they wanted their stockers to run as fast as a race gun…and often immediately noticed that the guns did indeed run faster…when they ran.
I found out a long time ago that the path to reliability is to slow the gun down rather than speeding it up. Slower cycling gives everything else the opportunity to keep up…notably the magazine. Because of the lower rearward slide velocity, it allows the use of reasonable recoil springs with no detrimental effects such as brass going into the next county and the dreaded frame battering that we hear so much about, but is actually much ado over…nothin’ much. The most important effect, though, is that the magazine can keep up with the slide. Next is that it makes the gun more reliable in locking the slide on empty.
So many good things happen when the slide runs slower, assuming that the gun doesn’t require overspringing for reliable full return to battery, and if it does…it still needs tweakin’. A 1911 that’s properly set up…and that doesn’t necessarily mean that they can’t be that from Jump Street…should feed and return to battery with a 12-pound spring. My litmus test is to hand feed a full magazine by pushing on the rear of the slide with one finger with the recoil spring removed. If it’ll reliably chamber like that…it’ll reliably chamber with any reasonable spring.
How does the small radius accomplish these wonderous things?
The slide cocks the hammer against the hammer’s inertial mass and the mainspring’s resistance. By lowering the point of contact on the hammer, it reduces the mechanical advantage, and ups the energy requirement in cocking the hammer. Because there’s only so much energy available…some of it used up in overcoming the added resistance. A simple matter of leverage.
But wait! There’s more!
By robbing the slide of some of its momentum…and robbing it as the instant that it starts to move…it adds a slight amount of delay. Delaying the slide…even a tiny bit…puts the bullet closer to the muzzle relative to the slide’s position. The earlier in the cycle that the bullet exits, the sooner the force is removed from the system…and once the force is removed, the slide can only decelerate.
At high speeds, a very small change has a telling effect. Newton 1A explains it. “An object at rest.”
The faster you try to accelerate an object, the harder it fights that acceleration. Simple physics. Adding just a little extra inertial resistance…which is akin to adding mass/weight…and the effect can be pretty dramatic.
Anyone can lift a 25-pound weight to a height of 5 feet if the rate of acceleration is 1 foot per second. Easy as pie. Try to lift that same weight…mass…at a rate of 100 feet per second, and it becomes a whole different kettle of fish. Add just 10% to the mass…and it filets, cooks, and serves up the fish on a bed of tartar sauce…and 10% is just pretty close to the change made by going from a 7/32nds radius to a 1/16th on the stop.
And I want to repeat, just for the record. I don’t use the small radius for purposes of recoil reduction. That it does have an effect on recoil is incidental, and was never something that I really considered beyond noticing it…determining why it happens…and ignoring it. Reliability is what it’s all about. That’s what I do.
As for the reduction in recoil, the physics behind it is fairly simple.
We recognize “felt” recoil mostly as muzzle flip, and the locked breech autopistol moves very little until the slide impacts the frame. A lot of that depends on the action spring, of course. The heavier the spring, the more the gun moves before impact…and vice versa. I’ve seen slow-motion videos of shooters with exceptionally strong grips in which gun movement was barely perceptible until the slide hit the frame.
Enter the small radius on the bottom of the firing pin stop, which lowers its contact with the hammer and reduces the mechanical advantage in overcoming the hammer’s inertial mass and the mainspring’s resistance.
By providing a tiny bit of added delay…think of it as a speed bump…the bullet escapes a tick sooner relative to the slide’s position…which removes the force that drives the slide sooner in its journey to the impact abutment. When that force goes away, the slide isn’t being accelerated. It can only decelerate.
The effect is two-fold. First, you have the speed bump at the outset, and you have the force removed from the slide earlier in the recoil phase…which reduces the slide’s rearward velocity and momentum…which translates to less impact with the frame…which translates to a little less muzzle flip. Aside from making the slide a little harder to rack, sometimes there is such a thing as a free lunch.
When I was making my own, and later…when I had the EGW stops to work with…I took it a step further, and made it even smaller than Browning’s 5/64ths. I used 1/16th for a time…and eventually just started breaking the corners lightly without shooting for a specific radius. That was due more to laziness and impatience on my part. It still takes time to set up for a precise radius cut with a mill when working with such a small part, and time to cut the radius precisely…so I just took the quick, easy route by swiping the corner a couple-three times on a smooth mill file and following up with a stone to smooth it.
I owe George Smith a debt of gratitude for his oversized square-bottomed stop. He saved me a lot of time at the bench. Making a firing pin stop from flat stock is fairly tedious, even with a mill to do the main cuts. If I ever meet him, I’m gonna buy him a steak dinner.
As a disclaimer, I have no vested interest in EGW’s continued success. I have received no money from George, nor any “freebie’ stuff outside of a specialized drill bit that he sent to me a few years back. If EGW failed tomorrow, the only pain that I would feel would be the loss of those firing pin stops.