[12Bravo]

It may very well be that your setup does NOT like standard velocity. Plus different bullet shapes/profiles can make a difference too.

 

[Baltimoreed11754]

Just tried it at 25-50-75-100 steps using the norma tac-22. Did not try anything else yet at distance. Shot off the back of my Tj. Had to drop to the first circle to hit my 2 inch steel at 100 steps. Tomorrow will be my first PRS .22 match so we’ll see. If I like it I might upgrade the glass.

 

[DrewBone]

A known problem. On CMMG's firing pin there are sharp corners present in the areas shown below; had there have been sufficiently sized radius' in these areas it would act as a fillet, creating a smooth transition where the two material surfaces meet at 90°, eliminating the starting point of the cracks that develop and lead to breakage:

Cracks and failures in machined parts can easily originate at sharp edges and inside/outside corners, so adding radius' to these areas is always a wise decision to help prevent unexpected material failures down the road.

I don't believe I've shot my dedicated CMMG .22 pistol rig nearly enough to raise concern, but I will keep an eye on things.

 

[12Bravo]

A known problem. On CMMG's firing pin there are sharp corners present in the areas shown below; had there have been sufficiently sized radius' in these areas it would act as a fillet, creating a smooth transition where the two material surfaces meet at 90°, eliminating the starting point of the cracks that develop and lead to breakage:

Yes this is a well known defect with CMMG firing pins. And they have since started machining a radius at each shoulder. @colonelhogan44, myself, and others have had in-depth discussions here and on ARFCOM on this exact subject.

I can tell you from personal experience that shafts and pins of all sizes can and will break at shoulders if there is not a radius machined in. I've seen enough roller shafts that are 24" in diameter or bigger break at shoulders due to shoulders being machined square.

 

[DrewBone]

Yes this is a well known defect with CMMG firing pins. And they have since started machining a radius at each shoulder. @colonelhogan44, myself, and others have had in-depth discussions here and on ARFCOM on this exact subject.

I can tell you from personal experience that shafts and pins of all sizes can and will break at shoulders if there is not a radius machined in. I've seen enough roller shafts that are 24" in diameter or bigger break at shoulders due to shoulders being machined square.

I hadn't heard about CMMG changing/updating their design, but that's great news!

Thank you for your time and effort along with the others involved in helping CMMG to address the issue and produce a welcome change in design

 

[zukiphile]

CMMG also finished the head of the pin the way Bore Buddy does. The new CMMG pins don't appear to be heat treated, or at least not with the same process as Taccom and Bore Buddy.

 

[colonelhogan44]

CMMG also finished the head of the pin the way Bore Buddy does. The new CMMG pins don't appear to be heat treated, or at least not with the same process as Taccom and Bore Buddy.

Taccom's pins are totally different material and HT than the BoreBuddy pins. CMMG's copy of my firing design is flattering I guess? Stress concentrations are sophomore level coursework in an engineering program, why you still see them showing up in things like production firing pins is totally a headscratcher to me...

 

[12Bravo]

Stress concentrations are sophomore level coursework in an engineering program, why you still see them showing up in things like production firing pins is totally a headscratcher to me...

And it is also taught to apprentice machinists too. One should never machine a square corner on any pin or shaft. A 1/64" or 1/32" radius is better than no radius. I would teach new machinists going through their apprenticeship to always put at least a small radius on their HSS cutting tools when sharpening them.

 

[colonelhogan44]

And it is also taught to apprentice machinists too. One should never machine a square corner on any pin or shaft. A 1/64" or 1/32" radius is better than no radius. Would teach new machinists going through their apprenticeship to always put at least a small radius on their HSS cutting tools when sharpening them.

I never design anything without a 0.015" or (preferably) a 0.030" radius on any inside corner of a turned part unless there is a really good reason it should be square.