This past weekend I let someone shoot my M4 as a way of introducing that person to the weapon.
The person wanted to shoot the rifle with the carry handle sight, so I reluctantly un-assed the Aimpoint T1 and LMT BUIS (I plan to put the Aimpoint on a QD mount so it was coming off in a few days anyway).
I mounted the carry handle all the way forward on the rail (flush with the front of the upper) and tightened the thumb nuts down as far as I could by hand, and then with a partial turn using a quarter. I know everything was tighter than Dick's hatband when I finished.
At the end of the range session, I noticed that the carry handle had backed off just a tad. Clearly, it was still mounted and still as tight as I made it, but the carry handle had obviously shifted rearward maybe 1/32 or 1/64 of an inch, just enough to expose a tiny bit of the front edge of the upper receiver. In other words, I mounted the carry handle flush with the front of the upper, and it backed off just a hair.
I could swear I remember reading recommendations that a mount be situated as far forward as possible because the final recoil impulse has a forward momentum and this should keep the mount from shifting. Clearly this did not happen.
I also have performed a couple of searches on this forum and I'm either mistaken about what I read or my search criteria just didn't pull it up.
It's kind of a moot point, because I'll be going back to the Aimpoint anyway when I get the QD mount, but now my curiosity is up. And I figure the same physics are happening to the Aimpoint's mount.
Should I loosen and re-tighten the carry handle mounted all the way forward and shoot it again to allow things to "seat" better?
Or has it shifted to its natural position (still good and tight), and I should just leave it alone?


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