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Posted: 12/28/2011 3:36:24 PM EDT
| I have two A2 configuration rifles that will not sight in (first time to sight these in). They both have DPMS barrels and standard handguards, one is 16 inch and the other is 20 inch. The 20 inch shoot way to the rignt, Its 3 inches right at the end of adjustment at 50 yards. The 16 inch shoots left took almost all the adjustment to get it center at 50 yards. Never had this problem before so not sure where to start looing for the problem |
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Who built the uppers?
Sounds like either both front sight barrel slipped to with the barrel nut clock wise, and why the FSB is canted to the left when looking towards the muzzle, and making the gun shoot to the right. To see if the barrels did really slip, shotgun both of the upper open and compare the center of the feed ramps to the front take down lug. As for solving the problem if it is that both barrel slipped and have the FSB canted to the left, you have the choice of either pulling the barrel and reinstalling it (read sending them back to be corrected), or slipping the entire barrel in the upper barrel socket to the needed correct index. To slip a barrel, upper receiver off the rifle, receiver on your left leg with the receiver firmly held alone, barrel across your right leg with the FSB just past your leg, then using a leather non marring leather mallet (large kind), make a sharp/hard blow to the FSB just above the barrel. This will slip the entire barrel in the upper socket via the FSB without shifting the FSB against the barrel. A note here, It could be that the barrel was installed correctly, but the barrel was not produced correctly; being that when the FSB was installed, it was indexed TDC with the barrel extension pin. In cases like this, when you check the feed ramps against the front take down lug, the feed ramp center line will be dead on the center of the lug, but you can see the front ramp canted. Also since I am taking about defects, it possible for the face of the upper barrel socket to not be true with the center line of the receiver/debris between once side of the upper barrel socket to the seating face of the barrel extension, of even the upper barrel socket being bent from over torque when the barrel was removed. If and when you run into problems like this, and the upper was factory assembled, return the upper back to the shop to have it corrected by them under warranty. 
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| The fsb on the 20 inch does not look to be canted. When I took the barrel off I found the barrel extention pin very loose and falls out easy. Going to have to order a replacement pin before I reassemble. I am looking at buying another barrel nut wrench as mine is a peace of crap. Suggestions on a real good quality one to buy? The one I have I picked up at a gun show. It works good on free floating barrel nuts where the three pins fit in the holes, but when using the other side on standard barrel nuts it just slips off when you have to go past 30 ft/lbs. |
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