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Posted: 8/15/2011 6:40:15 AM EDT
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I've just put together a dedicated .22lr upper using CMMG barrel and bolt, mil-spec upper and a Troy TRX rail - to mimic the configuration of my other 5.56 upper.
It runs fine, however I'm having problems zeroing it using the rail mounted BUIS. At 25 yards, it shoots about a foot below the point of aim, with the front sight post turned all the way down. Unless I trim the FSP in half, there seems to be no way to get it on target. Is it normal for .22s to shoot low compared to 5.56 uppers, or is my BUIS out of spec? |
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At what distance is the front sight from the rear sight?
Is it on a faux FSB? Are the front and rear BUIS on different rails, as in one on the upper receiver and one on the forearm's rail? Lay a straight edge, I use a steel rule, along the bore's axis on center top of the rails, and look to see if your two rails are in the same plane. The edge must have no gap along its entire length and the rails. Some rails (like some by DD) have a mounting system that will actually raise the front of the rail by 1/16 to 1/8 inches if care is not taken when assembling to the barrel nut. Depending on the method of attachment, if you have a "banana" rail, you can sometimes remedy it by applying careful torque, checking after every few turns with the straight edge. But some mounting systems may not allow for corrections, like those of the threaded tube type that thread directly to the barrel nut. If they aren't on the same plane as the receiver, they must be returned to the mfg. as they are out of spec. Ted |
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Figured it out. My TRX Extreme handguard is canted upwards. It wasn't immediately obvious to the naked eye, the barrel looks centered in the rail at a glance, but when i put it the whole thing on a level surface I could see that it's not perfectly in line with the upper, the front of the rail is slightly raised.
I am also unable to correct it: the thing simply clamps to the barrel nut, and no matter what adjustments I make, the handguard always returns to the same position once the screws are tightened. I'm probably not gonna bother returning it, just shorten the front sight post and call it a day. |
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