AR Sponsor
Posted: 8/29/2013 12:10:00 PM EDT
|
Being new to the AR, I sought the help of a friend to help with my first AR build (not my first AR). He had built several in the past and trusted him to do mine.
Unfortunately, he did several things wrong as I'm now coming to discover. When attaching the muzzle device we simply left the upper receiver in the same upper receiver block as used for installing the barrel and barrel nut. I'm now told this is a no no as it puts torque on the barrel pin, which can damage the upper receiver. Worse still is that these are billet matched upper and lowers. I did not use a whole lot of torque, maybe 20 ft-lb. and there does not appear to be any damage to the slot on the receiver. However the upper and lower receiver fit now have a minute amount of wiggle to them. The wiggle is still way less than any of my forged receivers, but there was absolutely no wiggle before when I fit them. I'm wondering if it's possible that I damaged the upper receiver when I torqued the muzzle device on. Or if the upper to lower fit simply loosened from firing 300 rounds or so. I now know to clamp the rifle just behind the muzzle device instead of using receiver blocks when installing a muzzle device. |
| You likely didn't damage anything. Fitting them together over and over again could have worn the finish down a little to cause it to wiggle. It may also be noticeable because you actually have leverage with the barrel, stock, and grip instead of two small pieces. |
|
Installing a FS with the receiver vise blocked, instead of the barrel, can end up with the barrel slipping in the upper receiver barrel socket, and the FSB/barrel not longer correctly indexed with the barrel socket. Here the problem will be that the rear sight needed a lot of windage adjustment to center the rifle.
As for the barrel able to move in the upper receiver socket, that is caused by the barrel nut not correctly tightened, and now the barrel loose in the upper barrel socket (barrel nut not retaining the barrel in the receiver correctly. On the barrel extension pin to the upper receiver barrel socket, tight or loose in the slot does not really matter, since one you have the barrel nut correctly tightened, you going to bore sight the rifle, and if needed, slip the barrel in the socket to index the FSB correctly. When doing the barrel slip to correct sight index, either the extension pin gets slightly bent, or it peen the side of he slot, and again, its the surface tension of the barrel nut to the barrel extension that holds the barrel in the upper receiver barrel socket correctly. Simply, the barrel extension pin is to aid in first installing the barrel in the receiver, but should not be thought of as a part that holds the barrel from slipping in the receiver instead, since there is a mater of tweaking involved once the barrel is bore sighted to get the barrel rotated to get the FSB indexed with the rear sight for a close to rear sight centered zero that can effect the pin to slot fit/mating. |
AR Sponsor