Looking for some wisdom on issues with a new AR...

AR/M4 AR Technical Discussion
1

I have a new AR that I have been working with and it has been giving me a headache. I am still trying to determine where the problem lies so I will leave out the names of the manufacturers until I can follow up with them when the problem is diagnosed (the ammo, mount, upper, and optic manufacturers in question are all very well regarded).

I bought a factory built upper receiver, mounted a new optic, and headed to the range to zero the new carbine. I ran a few hours of drills and by the time I got around to zeroing, I was hot and exhausted so I assumed it was just poor performance when I couldn’t turn in a group smaller than 6" at 100 yards. I did finally get what I thought was a rough 100 yard zero before heading home.

Roughly 2 months later, I was going to be taking part in some drills that the carbine would be well suited to so I pulled it out of the safe. I started the day working at 50 yards and in. My target looked a bit more shotgun-ish than usual and all impacts where left of center. I wrote it off as being rusty and probably not controlling the trigger as well as I should.

Then I took the carbine back to 300 yards. The optic on this rifle should make hitting the 2/3rds size silhouette steel we were shooting fairly easy. Instead, after much trial and error I found that I had to hold 12" low and 12" right just to get a hit on the 9 o’clock edge of the steel and even this wasn’t very consistent. I checked the mount right there on the 300 yard line and there was no detectable movement.

I took the rifle to 100 yards to get it on paper and my first 5 shot group was 3" high and 3" left which made sense based on how the rifle was behaving at 300 yards. However, the group was 5-6" large from a rifle/optic/ammo/shooter combo that I expect better than 3" from. The optic uses 1/2 minute adjustments so I dialed 6 clicks down and 6 clicks right.

When I shot another 5 shot group to confirm my adjustments, I found that the group was now on for elevation but was stringing right with the center of the group printing about 5" right of POA. 6 clicks (1/2 min adjustments) had moved my POI to right 8".

I began to question whether or not I was getting the whole story from 5" groups so I returned the windage adjustment knob to where it started and shot 2 10 shot groups (with a target check in between). These groups resulted in no discernible patterns. I couldn’t make any adjustments based on what I was seeing on the zeroing target. The impacts were all over the zeroing target which was printed on a 8.5x11" paper.

I was almost out of time so I handed the rifle off to another shooter to confirm that it was not the good behind the rifle that was causing the problem. He shot a 5 shot group that was about only about .5" wide but strung vertically over 6-7".

I was out of time for the day so I cased the rifle and brought it home. When I was home I rechecked the mount and it was solid. I checked that the free float rail is not making contact with the barrel and it was not. I pulled the rail and checked the barrel nut and it was torqued properly. I checked the muzzle device for signs of strikes and there were none. The bore is clean, clear, and looks good. The ammo is the last 240 rounds from a case of ammo that I have had no issues with.

At this point, I am thinking that the optic (which is new) is the issue. I still need to try some different ammo in order to completely rule out an ammo problem.

I plan to try new ammo, try the optic on an different upper that I know performs, and shoot the problem upper with a different optic. This should narrow the problem down to either the upper or the optic.

Is there anything else that I should check? What am I missing?

2

I had a similar problem. The only way I found it was my optic was I flipped my buis up and tried to cowitness. Did you try this? I know how irritating it can be, especially with a new piece of equipment, but it does happen. That’s all I can offer that you haven’t tried already.

Good luck.

3

Thanks for the feedback. It is a variable power magnified optic so co-witnessing won’t be possible.

4

Irons or back up sights?

I seen NO mention of using irons.
Thats the first thing I would have done, sight it in before I mess with an optic

5

Change one variable at a time. Either change the optic or the ammo. If you change both, you won’t know which affected the groups. Your idea of swapping the optic to another lower and trying a new optic on the problem upper is a good one

6

If have available some other glass, swapping it out is the easiest option so it should be your first option.

7

Also, when shooting from the bench, was the barrel rested or being pressed on something? Only the rail should touch a sandbag.

8

I dont think that would make a noticeable difference to the point he is mentioning. I rest my M4 every week and I get 1/4" groups.

I would put my money on the sight.

Did he say what brand optic it was? Nevermind that. I forgot about the “Down low”

9

I do have back up irons and I will be verifying them on this next trip to the range. I suspect that you are right and they will tell a lot of the story.

It is a 16" barrel that is covered with a 13" rail. There isn’t a lot barrel left to make contact with anything. Most of the groups were shot from the prone using the magazine as a monopod anyway.

Thanks for the input guys.

10

Thats something I would have done first.

Always start with the easiest/cheapest. Then work your way up

11

Get some ammo that has a KNOWN reputation for being good and reliable. Take the optic off and then use the iron sights. If it is still all over then you know the issue is more than likely the barrel.

Nothing is foolproof or 100%. You could have a 2K scope and it could be fucked. You could have a 1500 carbine and it’s shooting screwy.

Try to eliminate the issue by removing the variables.

12

I agree with Iraqgunz, but I would also throw in your scope mount as a possible cause. Trying good ammo with iron sites will eliminate some of the variables.

13

I agree. It happened with my ACOG once even after I thought the screws were tight and Loc-tited.

14

Thanks guys. I am tracking. I’ll try to remember to report back and list the gear involved once the manufacturers have had a chance to make things right.