Need Help with Diagnosis

[lamazza]

The rifle in question is an Armalite AR10.
In the beginning..
I bought this used. The first time out to the range I started shooting about 3 inches off at 25yds. After Zero at 25 I noticed the rear sight had to be adjusted about 6 clicks left.
Shooting at 100 yds, once again off center about 3 inches more adjustments and the rear site is pretty close to reaching the end of left sight adjustment.
200 yds, same.
Frustrated I decided to use a level and noticed that my front sight was slightly canted.
Took it to a local smith to see if the barrel could possibly be bent. Local smith said the barrel is not bent and ,as far as they could tell, the problem is occuring from the front site to the bore...
I sent the whole upper to Armalite where they replaced to front sight and did the 'upgrade'.
Get the rifle back and take to it 25 yards...shooting 3 inches right and zero to same, more or less, rear sight adjustment.
Ditto previous results for 100, etc.
Even though the rifle is shooting to the right I am getting phenominal groups-about 1-1/2 inch at 100 yards using open sights.
I am completely at loss as to what my next step should be to correct this problem.
Any ideas would be appreciated.

 

[rbernie]

I presume this is an A2 model?

 

[lamazza]

Yes, A2.

 

[86thecat]

Is the barrel canted? If so you might check on AR15.com forums, in the build it yourself forum there is a build lower etc sticky- at the bottom of replace barrel there is a faq about fixing a canted barrel.

 

[lamazza]

Thats interesting 86.
Which may mean that I've wasted money by sending this to Armalite AND it would now mean that the FSB has been erroneusly adjusted.
I would think that an Armalite gunsmith would catch that, but who knows these days.

 

[rcmodel]

Canted barrel or sight.

Is the front sight/gas block pinned, or clamped with socket-head screws?
If it's screws:
Loosen them slightly and bump the sight/gas block over to the left slightly.

If it's pinned:
Loosen receiver locknut and turn the barrel slightly then tighten the nut back down.

Or call Armalite back up, and ask them to issue you a call-tag so you can send it back a second time for free.
Maybe they will get it right the second time around.

BTW: I would closely inspect the gas tube for unusual wear or bending.
If the barrel is canted that much, the gas tube may not be lining up with the carrier key properly either. That is sure to cause problems down the road a ways.


rcmodel

 

[lamazza]

Thats just the thing rcmodel.
The gas tube looks fine and-to my naked eye-it looks straight.

 

[rcmodel]

Well, I suppose it could just be a bad barrel.

I have a Like-New Winchester 61 made in 1953 that shoots way off the sights like that, and nothing I can check indicates a bent barrel, buggered crown, or anything else wrong with it. Some things you just can't explain, or find a cause for!

I'd call Armalite again and discuss it with them.
Maybe they will put another new barrel on it this time around.


rcmodel

 

[raz-0]

Usually with a canted barrel or sight, you can't fix the error with just windage as the front sight is not only left or right of where it should be, but lower.

IIRC one way to diagnose this, especially if you are getting nice tight groups, is to adjust the elevation of the front sight, and see if is causes you to have to change windage to get vertical alignment with your point of aim that you previously had.

Of course, it is possible for a barrel to just be bent and out of spec.

 

[lamazza]

All good advice-thx all.
I'm going to try putting one of my fixed power scopes on it and see if it holds
POA at different distances, if that doesn't work, I think its back to Armalite.
I really am not thrilled with the prospect of spending money for a new barrel.

 

[rcmodel]

That test won't work with a scope.
You will have to shoot it with the iron sights to do what raz-O suggested.

A scope could care less if the barrel is turned 1/2 a full turn in the receiver. It's still going to shoot in pretty much the same place.

With the iron sights, an elevation adjustment will also change the windage if the front sight is canted.


rcmodel

 

[86thecat]

I'd have the upper checked before buying a new barrel just to be sure, if it's not machined square a barrel might not make any difference.