AR Upper & Lower Fitment & Accuracy

stanley_white · Oct 23, 2024

I understand the party line is that upper to lower fitment on an AR rifle doesn’t effect accuracy.

However, has anyone ever tested this?

I am envisioning someone who isn’t me taking an AR and installing the smallest takedown pins possible, to maximize rattle between the upper and lower, testing the accuracy, then installing the largest pins possible to minimize rattle, and shooting the same course of fire, and noting the results.

Or some other similar experiment etc as everyone is smarter than I am on the subject.

Has anyone done anything like this?

-Stan

Bantam1 · Oct 23, 2024

My 18" AR in 5.56 has a small amount of slop between the upper and lower. It is not much but it is there and allows the upper to rock side to side. I found that shooting from the bench with normal bipod load and no loading anywhere else, the groups open up slightly. If I grip and give a little left twist to apply some load to make the slop between the upper/lower go away, the groups will shrink back down. Upper is a Centurion with the Douglas barrel. Lower is an old Bushmaster from the 90's.

The difference is about 1/4 MOA. Not enough to really worry about since my handload is .3-.6 MOA if I am not lazy when shooting it for groups. If I get lazy it will be under MOA no matter what. So good enough for the targets and distance I shoot the rifle at. I was going to drill and tap the lower to install a tension screw and just never did with that lower. Maybe it will be a tiny bit more consistent, maybe it won't. I just never let it bother me since it's an AR. I could swap with one of my other lowers that have tension screws to see, but once again it wasn't that important to me. It shoots really well inside of 700 yards. Good enough for the cartridge and a gas gun.

LRRPF52 · Oct 23, 2024

Bantam1 said:
My 18" AR in 5.56 has a small amount of slop between the upper and lower. It is not much but it is there and allows the upper to rock side to side. I found that shooting from the bench with normal bipod load and no loading anywhere else, the groups open up slightly. If I grip and give a little left twist to apply some load to make the slop between the upper/lower go away, the groups will shrink back down. Upper is a Centurion with the Douglas barrel. Lower is an old Bushmaster from the 90's.

The difference is about 1/4 MOA. Not enough to really worry about since my handload is .3-.6 MOA if I am not lazy when shooting it for groups. If I get lazy it will be under MOA no matter what. So good enough for the targets and distance I shoot the rifle at. I was going to drill and tap the lower to install a tension screw and just never did with that lower. Maybe it will be a tiny bit more consistent, maybe it won't. I just never let it bother me since it's an AR. I could swap with one of my other lowers that have tension screws to see, but once again it wasn't that important to me. It shoots really well inside of 700 yards. Good enough for the cartridge and a gas gun.

Drop an Accu-Wedge in it and be done.

AMU did some testing on all of this. I think the main thing is instilling shooter confidence in the rifle when it feels solid, vs sloppy.

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AR Upper & Lower Fitment & Accuracy

stanley_white

If it ain’t broke, you can’t resist.

Bantam1

Gunny Sergeant

LRRPF52

Sergeant

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