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Posted: 8/19/2009 10:01:45 AM EDT
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I added a yankee hill ff to my BCM middie and it is shooting way to the right about 8 inches at 30 yards. When I started the disassembly the front sight base pins were a real pain to remove even after a good soak with lube. Is there some way that the front sight base shifted to the left a little after pounding those pins out or can the base be out of "square" after reinstalling? I used a brass punch to remove the pins. Actually 3 brass punches. The reason I say its the front sight is that I have to adjust the rear sight nearly all the way to the left to get it on target. Since I didnt fire it before the ff was installed I have no basis for its original accuracy. The rear iron sight is a cut down RRA tactical carry handle that is perfectly accurate on the rifle it came from. I have not tried a different rear sight but would it matter anyway? |
| The barrel was supported on a bench when the taper pins came out, the taper pins came out in the right direction, I used brass punches not titanium, the barrel nut is definitely tight. The taper pins were not replaced on reassembly- is this critical? How accurate are BCM uppers since I fucked with mine before I shot it? |
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Quoted:
The barrel was supported on a bench when the taper pins came out, the taper pins came out in the right direction, I used brass punches not titanium, the barrel nut is definitely tight. The taper pins were not replaced on reassembly- is this critical? How accurate are BCM uppers since I fucked with mine before I shot it? You removed the taper pins and didn't replace them? Put them back in and check again. BSW |
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So are you sure the barrel didn't jump the index on the receiver when you installed the YHM nut? I wasn't aware the barrel could jump the index but I'm sure it did not. Here's another thought. The barrel nut was hand threaded then torqued to the next hole to line up the gas tube but it was not enough. I cant remember exactly but it was less than thirty ft lbs. So I had to torque it to the next hole on the barrel nut which took some effort and it torqued in the high 70's. What's the possibility that it was torqued too much? |
| There should be no problem with re-using your tapper pins. As long as they are not marred up or bent, they are perfectly fine to re-use. I would first start by taking the upper apart and re-assemble from scratch. When you torque the barrel nut, make sure the nut and the treads on the receiver threads have a good high temp grease preferribly containing moly. When you torque the barrel nut, do it three times. Torque it down once then unscrew it, then repeat this two more times until the nut is lined up with the gas tube hole. This will help to relieve some stress on the receiver. If after doing this, the upper still shoots too far to the right. Try installing another FSB. Since you don't know if was shooting to the right to begin with, it is very possible the FSB could be the problem. |
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