AR Sponsor
Posted: 4/17/2006 8:03:29 PM EDT
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I'm new to ARs so bear with me.... I got a brand new BM in December and sighted it in following the instructions from Bushmaster. I've noticed a rather significant change in zero when the barrel gets warm. I'm shooting clays at a range of about 175m at a rate of 1 trigger pull about every 10-15 seconds. When I go through about 20 rounds or so I notice the point of impact raise about 6-8 inches resulting in me aiming lower than normal. I thought it was my eyes playing tricks but my buddy said he noticed the same thing. Now that I think back to when i sighted it in, after a shooting a few rounds, my groups started rising and i adjusted accordingly to get a zero with a warm barrel. I'm using the small aperture, same aperture i used to sight it in. I have a 1:9 twist barrel with 5.5" flash suppressor, A3 removable sights. I shoot Winchester 55g and Black Hills reloaded 55g FMJ .223. I don't know if anybody else has experienced this problem but any advice will be appreciated. Thanks in advance. |
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Welcome to the site!!!!!!! Now the basics, In High Powder rifles, you are burning lot of Gunpowder, which creates a lot of heat. Unlike a 22 rim fire rifle that you cannot really over-heat, you can with the AR in regards to shooting groups. But, what this should translate to is a size increase in the groups, and not a total shift of impact. What in fact sounds like is happening is that the barrel in not tight in the upper (loose barrel nut) and as the rifle heats up, the barrel is allowed to whip more freely (and maybe combined with hand pressure as well). To see if the problem is as simple as the barrel nut being loose, just pull the hand guards and see if you can move the barrel nut by hand (the star nut, and if loose, it should rotate a little back and forth). Since you are new to the rigs and really not sure if you are tooled up, if you do find some movement in the barrel nut, then a quick call to Bushmaster should resolve the problem. |
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