Is it the rifle? the scope? or the mounts?

[rcummons]

I am reasonably new to the ar rifle. i first bought a cheap DPMS sportical in .308 with the 16" barrel. i put a redfield LE 3-9 scope on it with burris XTR rings and had lots of fun with it. it would reliably group 1.1 - 1.2 at 100 yards and under four inches at 300 yards which is the furthest range available to me.
now. i wanted a rifle to try and get moa or better so i bought a DPMS LR 308 with an A3 upper and what appears to be a 20" barrel with an integral muzzle brake. i mounted a SS 10X42 originally with Burris XTR high rise rings. i was unable to zero at 100 yards. with the scope cranked all the way to the stop it still hit about 8 - 10 inches low at 100 yards. figuring the rings were too high i then bought the lowest XTR rings i could get but the scopes sunshade came in contact with the free float tube. i then bought a 1/4" riser to get the scope off the tube and it still hits 4 - 6 inches low at 100 yards. whats the best guess? is it the rings, the scope, the rifle? or could i be doing something wrong? the rifle was ordered straight from DPMS so i dont believe anyone has messed with it i have fired german surplus 147 grain nato, Winchester white box 150's PMC bronze 147's and Federal gold medal 168's and they all hit low.

 

[KNIGHT11B4]

Re: Is it the rifle? the scope? or the mounts?

Your POI is that low and you have no more travel UP in you SS?

You elevation is topped out?

 

[rcummons]

Re: Is it the rifle? the scope? or the mounts?

Yessir the elevation is either capped out or it got stiff enough to make me afraid to crank any harder ;-P i am firing at a 12" shoot n see sittin about 15" off the ground and i hit about two or three feet behind the target. i am shooting at a slight downward angle bc i am on a four foot platform sitting at a bench so i am guessing the rounds are passing a couple inches below the target when i aim at the bullseye.

 

[acidone]

Re: Is it the rifle? the scope? or the mounts?

Try removing the upper from the lower, pull the bolt and carrier, set the rifle in a rest, and literally look down the bore and get the target centered to the opening at the end of the bore. That's where the bullet should go Maybe an 1-2 lower, but pretty much there. Then you can move you head up, without moving the upper, and see where you POA is which the scope. Then you can see where you need to go. I had a similar issue with an LMT 5.56 upper and it turned out to be a chamber that didn't line up with the bore correctly. You may be experiencing the same type of issue. No offense, but if it's possible out of a "mil-spec" company like LMT, I have no reason to believe it couldn't happen with a "commercial spec" gun like a DPMS. Good luck and I hope this helps

 

[ROCKRIVER308]

Re: Is it the rifle? the scope? or the mounts?

I would say that it is NOT the rings. I have about six sets of those rings currently in action, no problems at all.

Have you used that scope on a different rifle? Did that scope work properly on the other rifle?

I would guess that the scope is the problem, but need more info.

 

[pepperbelly]

Re: Is it the rifle? the scope? or the mounts?

Put that scope on another rifle and another scope on that rifle and see which has the problem.

Jim

 

[c ward]

Re: Is it the rifle? the scope? or the mounts?

First thing I would do is put a target backer large enough to impact behind the target to know for sure where the rounds are impacting instead of guessing . After that swap the scopes between rifles and see what happens .

 

[douglas13]

Re: Is it the rifle? the scope? or the mounts?

I had the same problem recently. The problem turned out to be the end of the of the upper is not perpendicular to the rest of the upper.

This error was fixed with a lapping tool. http://www.midwayusa.com/viewProduct/?productNumber=810457

The prolem was not obvious until the lapping was started with the tool.

Doug