I was at the range today zeroing a new Aimpoint T-1 on a 16” middie with MOE handguards.  I zeroed using a benchrest and then when I shot standing I was shooting several inches low.  It seems like the benchrest was putting pressure on the barrel making it shoot about 3 inches high at 50 yards.

I had to zero my AR without the benchrest just resting my elbows on the bench.  Then I tried the benchrest again and was about 3” high.  I have never experienced this large a POI shift using a benchrest before, although this is a new benchrest and I had to rest the handguards right near the frontsight to get in front of a VFG I added whereas I usually put the rest closer to the receiver.

Is this amount of shift in POI expected when resting non-free float handguards on a benchrest?  I thought the shift should be much smaller than this.  

Thanks

Barrel nut properly torqued?

Thats wild. I just sighted one in and actually tried to get a shift in impact and could not make it happen. I was using my rock JR rest and then I shot free hand and a few shots I sorta torqued on the gun using my VFG. The reason I was doing that was because I heard someone saying that you "can't" sight in using a rest with normal hand guards. I'm new the the AR so I wanted to try it for myself. Anyway's, it was fine for me. I guess at long ranges or a real hot gun it could make a difference. I was shooting at 50 yards using the Aimpoint site in targets.

That happened to me every time I zeroed in the Army. We zeroed with sandbags and a bench at 25 yards, but shot unsupported and kneeling. I kept hitting low, even on the 50 yard targets.

Once I started zeroing with my hand under the hand guard (applying to downward pressure), my groups opened up a bit but I achieved a consistent zero.

different shooting positions especially offhand/standing will cause poi shifts even in match guns- a lot of very good highpower shooters have different zeros for offhand sitting and prone even when shot at the sane distance. nothing is wrong with your rifle

Thanks for the replies all.  I think the barrel nut is properly torqued since the rifle will still group well, just POI shifted up when using the benchrest, but I don't have an upper receiver block and barrel nut wrench to make sure it's good.



I know there will be some POI shift, but I thought it should be a lot less than I was experiencing.  You're saying 3" at 50 yards is normal?  

I'm planning to go back to the range tomorrow.  I'm going to try the benchrest again and see if it makes a difference if the rifle is resting closer to the front or back of the handguards.

No, it's far from "normal".



One inch or maybe two at 100 might be more like it, not 6" at 100.



That's why I questioned the barrel nut.



 

I agree with OlCrow. That isn't a normal shift in POI.
Could it be your cheek weld position between the two positions?
Dave N

Are you sure the barrel wasn't touching the rest at all?  This will definitely have an effect on your POI.  I've accidentally rested my barrel against a barricade before and all my shots went high.

If I recall properly, the issues he speaks of (mostly to do with perception of the iron sights at varying head positions) should be minimized (or erased) by your red dot being "parallax free".  I would say (as an amateur compared to many here) your shift is extreme but not impossible.  Are you bearing down on the gun when shooting bench?  I got about 4" in shift at 100 yards by using a loop sling before I floated my gov profile barrel.  The idea of checking your barrel nut torque isn't a bad idea but don't over-torque it.  I'm pretty sure the USAMU keeps in the lower half of the torque spec (maybe that was the flash suppressor).  Good luck!

Thanks again everyone for the replies.  As Jonnysixguns mentioned I was using an Aimpoint which is parallax free so a different cheek weld shouldn't be the issue.

I realized after I got home for the range the other day that it may have been the barrel resting on the benchrest and not the front of the handguards (b/c the VFG was getting in the way).  Would resting the barrel directly on the benchrest cause more of a shift than resting on the handguards (which put pressure on the barrel through the handguard cap)?

I removed the VFG and went back to the range today.  At 25 yards resting the handguards on the benchrest caused it to shoot 1" high, a little better but that's still a 4 MOA shift.  It didn't matter whether I rested the handguards on the benchrest closer to front or back of the handguards.  And I wasn't pressing down hard on the rifle, just resting it on the benchrest.

As I mentioned I don't have the tools to check the barrel nut torque and don't want to send the upper back to the manufacturer if I don't have to.  The upper now has 700 rounds through it with so far 100% reliability.  The only way I can think of to check if the barrel nut is properly torqued is that if it were loose the rifle wouldn't be able to group well, right?  Me being a crappy shot makes this difficult to test, but at the end of the range session today I shot about a 3" 15 round group at 50 yards, not using the benchrest just resting my elbows on the bench.  Not the greatest group, but would a loose barrel nut shoot even larger groups than this?

Thanks!

Update:  I emailed the manufacturer to see their thoughts on this.  They said this amount of POI shift is normal.  I guess my upper's POI shift is maybe just on the high end of what's considered in spec?  Now I'm interested to see how much the POI shifts when using a sling, will try that next time I make it to the range.

+1 NTCH

That's not normal. You really have to crank on a sling to see any visable POI shift without freefloaters. You should check your rifle, and then check your position.

Topic Moved

I do shoot nose to the charging handle.  Also, see above, I was using an Aimpoint so cheekweld/head position shouldn't make a difference.



Any ideas how to do this without an upper receiver block and barrel nut wrench?  Not sure what else to look for besides a loose barrel nut.

Just thinking out loud here....

When shooting from the bench rest there was upward pressure on the barrel, whether significant or not.

You said you had a VFG on there as well. When standing were you using a handhold that would cause lots of downward pressure when using the VFG? I.E. pulling the VFG tight to your shoulder?

That would give you some higher placed shots from the bench, and some much lower shots when using the VFG.

I'd be curious to see where shots went if you could shoot with no support on the barrel/handguards at all.

Hi pbnut, thanks for your reply.  That would definitely make sense if I were pulling hard on the VFG I could essentially double the POI shift, moves up on the benchrest and down with the VFG.  However, that doesn't seem to be the case here.  I also tried shooting with my off hand on the magwell so nothing was touching the handguards/barrel at all and got the same POI as when holding the handguards.  

Next time I go to the range I'm going to try some more tests to see when and how much the POI moves, such as shooting with a sling, trying different benchrests, etc., but I can't make it to the range again for a few weeks.