A couple of points...
The stops are available in Series 80 and pre-Series 80 types. The one shown here is a Series 80.
A true radius isn't absolutely necessary. In fact, George recommends a light bevel for those not adept at creating a clean radius with a file...and it works well.
The original specs called for a nominal .078 radius, but it varies from .075 to .080 inch. I've cut it as small as a 16th (.062) and as large as a 10th inch...depending on the application. i.e. The longer the slide, the smaller the radius. Remember that as the radius gets smaller, the more it resists the slide's rearward movement...and the more momentum it loses at the outset.
Commanders get .075 or so. 5-inch guns get a 16th. Officer's Model/Defender class get the 1/10th inch radius. Although that seems backward, remember that the slide's momentum plays a big role in taking it to full rearward travel. When the radius causes it to lose a lot of that at the beginning of the cycle, you can run into short-cycles if you go too small with it. I'm also a "Light Springer"...that is...I tend to go down on the recoil spring loading instead of up, and use standard 16-pounds in 5-inch guns...standard 16 pound springs trimmed to 24 coils or so in Commanders...and clip the inner springs on dual spring systems in the chopped guns in order to prevent mag timing issues on the RTB. So...adjust the radius accordingly. Start with a small one and test it with the recoil spring that you intend to use, along with a new mainspring. If you go with a lightened mainspring, you can get away with a smaller radius...and don't under-estimate the effect that this firing pin stop will have on the slide's rearward speed and momentum. I've seen guns that throw brass 10-12 feet change to dropping it 3-4 feet away with just the addition of a .062 radiused stop and a new standard mainspring...and I've seen guns that throw it the "ideal" distance of 6 feet, barely dribble it out of the port.
The additional benefit is that the stop is oversized and can be carefully sized to a light press-fit...which eliminates extractor clocking and having the stop fall out of engagement and tying up the gun if you let your firing pin spring go too long between changes. It's the best 15 bucks that you ever spent on your pistol.
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