Marking cam pins?

[jerrysimons]

There is an error in your logic.

The cam angles for locking and unlocking are equal, the bolt carrier is a cylinder and the cam pin is a cylinder. This means the contact areas as the pin moves forward are exactly the same as the contact areas as the pin moves backwards only rotated 180 degrees. That means the wear areas are exactly the same.

The increase "slop" is caused by and increase in clearance between the parts, so if you want to reduce your shock loading, you want to reduce the amount of wear. The pin is softer than the carrier so most all the wear in on the pin.

The loading during the unlocking camming is much greater that the loading during locking camming, therefore the "front" of the pin will wear faster than the "back". If you keep one side towards the front all the time, the front wear will accumulate faster than the back. If you switch pin orientation regularly, or randomly, the wear will be distributed equally on the front and the back of the pin, so on average the amount of wear on any one face will be less.

Also, the cam pin does not bottom out in the cam track during locking, the carrier stops on contact with the barrel extension well before the pin reaches the back end of the cam slot, so this side doesn't wear at all. The highest load on the cam pin is at the end of unlocking when the pin bottoms out at the front of the cam slot. Again, randomly switching the orientation of the cam pin will reduce the wear on any one side.

If you want to reduce the loads on the hole in the bolt, the way to achieve that is find a way to reduce the amount of wear on the face of the cam pin that faces forward. Flipping it 180 degrees every now and again is a better way to do that than leaving one face always facing forward....

Personally, I think liberal use of a good lubricant in the cam slot is a most cost effective way of achieving the desired end.

Agreed a good lube that stays put like a light grease is ideal there. But the error here is thinking this is about cam pin life and not bolt life. The carrier track is not the only wear point on the cam pin, the twisting open action wears the cam pin inside the bolt hole. That is where the slop can be real bad especially if you started with a wiggly cam pin inside the bolt hole to begin with. The bolt is holding onto the pressurized case and carrier is flying rearward, the connection point between the two is a shaft inside a hole 90* to the momentum force, when cam pin hits bottom in the carrier track during unlock, the cam pin applies pry forces to the bolt at the bottom-muzzle-side and the top-buttstock-side of the bolt cam pin hole via force applied on the top-muzzle-side of the cam pin by the carrier track (this same principle is why Knights reinforced the E3 bolt at the cam pin hole by reducing the diameter of the cam and cam pin hole hole). The wear on the reverse side of the cam pin at the carrier cam pin track is not really at issue, like you said because the cam pin only bottoms out in the track on unlock. The slop issue is the wear of the cam pin inside the bolt hole and the pry forces that happen during the shock loading of unlocking.