4 MOA with a new AR barrel.

[baekacaek]

Update: Tried some 75gr Hornady BTHP and got about 3/4 MOA with a Mil-Spec trigger. Seems I'll be using 75-77gr bullets from now on.

4MOA vs 3/4MOA? Hmm...

Maybe your barrel is very particular with ammo. Didnt expect that big of a difference.

[HollowOfHaze]

At first I thought it might have been me, so I switched between Hornady 55gr and 75gr BTHP with each reload, and the accuracy disparity was consistent. I think my barrel just likes that weight. I am not capable of reloading on my current budget.

[Scratch705]

have you tried 69gr?

i mean seems weird that your 1in8 twist only prefers the high weight bullets when the selling point of 1in8 is the fact that is should stabilize nearly all the weights that a typical AR would see. from 55 to 77

[GM4spd]

Most likely they are FMJ and the jackets are thick and the base of the bullet is inconsistent. No match bullets have the jacket open at the base.

This is very true, but I've seen over the years most of my AR rifles would
shoot 55 grain into two inches at 100 yds with no problems. The same
rifles would shoot 5 shot groups into 3/4" with 55 grain Match bullets that
were handloaded. These were 1-7" twist barrels.

[ProtectThe2nd]

This is very true, but I've seen over the years most of my AR rifles would
shoot 55 grain into two inches at 100 yds with no problems. The same
rifles would shoot 5 shot groups into 3/4" with 55 grain Match bullets that
were handloaded. These were 1-7" twist barrels.

yup...I don't think the OP should be try heavy weight rounds to solve his issue...

Something else is going on

1-8 twist should throw 55s into 2MOA or better all day long as long as it's decent ammo (although I'll omit Tula/Wolf steel from that expectation)

[ar15barrels]

However, what are barrel nut shims for?

To achieve correct timing at a more desired torque.
If your barrel nut is aligning at around 25 and you took it to 60, it's not going to make it to the next hole/tooth.
A shim will allow you to get alignment at a different torque range, either higher or lower than where you are without a shim.

[highpower790]

4MOA vs 3/4MOA? Hmm...

Maybe your barrel is very particular with ammo. Didnt expect that big of a difference.

feed your rifle cheap mass produced ammo and most likely you will see poor results.Why spend hundreds on a good quality rifle to feed it garbage.garbage in ,garbage out.

[michael1one]

OP, check out the photos below. I built an upper with a new barrel using the standard armorers wrench and no barrel nut shims - it was tough getting the gas tube hole lined up and thought I had the nut torqued tight "enough". Took it out to the range with a 4x scope and good ammo carefully hand loaded from match grade components. And got >4 MOA and said WTF? Those orange dots are 1" diameter.

Then I invested in a torque wrench and a better barrel nut wrench to fit it. Bought set of barrel nut shims off eBay for a few bucks. Reset the barrel and ended up using 3 shims beneath the nut to get torque at 60 ft/lbs with the gas tube lined up. Took that back out to the range with some of the exact same batch of ammo from the first disaster and got then got 1 MOA in the right hand photo (sorry for the crappy focus from cell phone camera).

I doubt yours will get better just by shooting more rounds or cleaning it. I would recommend investing in a torque wrench or borrowing one over head space gauges or checking that.

Oh man. I can't wait to try this out. My last upper just isn't shooting very well. I thought it was a barrel, but maybe i need shims and more torque. Thanks!

[teflondog]

The best I've done with factory Federal American Eagle XM193 is 2.5 MOA and that was on a really good day. It usually shoots 3-4 MOA out of my barrels. You need to either buy better ammo or start reloading if you want good accuracy.

[HollowOfHaze]

The 55gr I used recently was Hornady, on suspicion that Federal was a bad choice. I'd expect that if anyone made good factory 55gr, it would be Hornady.

[ScottsBad]

yup...I don't think the OP should be try heavy weight rounds to solve his issue...

Something else is going on

1-8 twist should throw 55s into 2MOA or better all day long as long as it's decent ammo (although I'll omit Tula/Wolf steel from that expectation)

Everyone thinks twist vs. weight determines stabilization. But length is more important than weight for determining the amount of stabilization. It just so happens that there is a bit of correlation between weight and length, but length determines the amount of engagement to the rifling.

[ozarkpugs@gmail.com]

When someone starts talking proper torque on barrel nut don't waste time reading anymore .The barrel and upper are machined to match and no amount of torque will change that ,the reason for torque range is 30 is tight enough it will not viberate loose and 80 will not damage threads if you go over you chance ruining upper and or nut .The poundage has absolutely no effect on accuracy or anything else 31 is as good as 79 and visa versa

Sent from my XT1093 using Tapatalk

[ProtectThe2nd]

Everyone thinks twist vs. weight determines stabilization...

Yeah...because it's in print EVERYWHERE...

the rest of your hypothesis doesn't apply to the AR platform

As peeps are aware the AR is like the AK a military platform not designed for sniper accuracy although SPR/DMR 1:7 twist variants were developed to toss heavy ammo with more accuacy than 55/62 grain loads.

Most military ARs have 16 or 18 inch barrels and are meant for mid range targets out to 300 +\- meters...the velocity between 16 and 18 is negligible

The point is the OP's 1:8 should throw 55 grain more accurately
than my 1:7 does...but mine throws 55 grain into 1.25 MOA all day
and 80% of the time it's a 1 MOA barrel

Having said that it only likes Swiss Geco in 55 gr and
doesn't like ANY Federal and numerous other rounds, at all...unless they are heavier

I think it's barrel torque and/or ammo, I'd try something other than federal military rejects and check your torque

[TMB 1]

Everyone thinks twist vs. weight determines stabilization. But length is more important than weight for determining the amount of stabilization. It just so happens that there is a bit of correlation between weight and length, but length determines the amount of engagement to the rifling.

Yeah...because it's in print EVERYWHERE...

the rest of your hypothesis doesn't apply to the AR platform

It is length and it applies to anything. That's why bullet makers make flat base, semi-spritzer and round nose bullets. That way you get a heavier bullet that will stabilize in slower twists. They also make boat tail spitzers that make a lighter bullet longer and need a faster twist.

[ar15barrels]

At first I thought it might have been me, so I switched between Hornady 55gr and 75gr BTHP with each reload, and the accuracy disparity was consistent. I think my barrel just likes that weight. I am not capable of reloading on my current budget.

Faster twist barrels REALLY show you the quality of the bullets.
The crappy 55gr bullets are out of balance the much-faster-than-required twist rate will cause the groups to open up accordingly.

That same crappy 55gr ammo would likely shoot better in a 1:12 twist barrel.

When you get into 75gr and 77gr ammo, most of the bullets are much better quality.
It also happens than the 1:7 twist is a much better match to the heavier (longer) bullets so the barrel is not really over-spinning them much.
The result is great accuracy.