Hi guys, new to AR15.com but I need a bit of help.

I recently swapped barrels and my optic on my ar and I feel like im getting atrocious accuracy.

Here are my specs
Primary Arms slx 1-6 Nova
Burris AR-Signature PEPR cantilever mount
Ballistic Advantage 14.5 barrel

These are what I've changed. And now at 100 yards I'm seeing 4.5"+ groups sometimes as much as 6". This is with AAC 55gr FMJ and Winchester Valor M855 62gr.

While im aware these aren't exactly target grade ammunitions, I feel like I should definitely be getting at least 3" groups.

Here's what I've done so far:

Checked barrel torque (50ft.lbs)
Reseated optic mount to reciever
Checked torque on rings (23in.lbs per manual)

Am I just expecting too much out of this gun or is something wrong?

UPDATE: It's not the optic or mount. I put them on my Ruger American predator 308 which I have proofed as a sub MOA gun. And was able to punch out a .75" 4 shot group.

So it's either a bad barrel or the barrel hates the ammo I'm using.

Barrel has about 200 rounds through it now. Groups haven't changed at all for better or worse.

I'd contact BA and tell them you got a crap barrel.
Hopefully they'll take care of you.

What are the specs on the barrel? BA 14.5" isn't much information. What chamber and twist rate? No barrel is going to shoot both 55 and 62 grain well. It would be good to have benched groups for each round. What muzzle device?

4.5" isn't a horrible group from 14.5" barrel using mediocre to poor ammunition at 100 yards. 6" is a little much but if the twist is poorly matched, I can see it.

Attached File


Winchester M855 is a regular poor performer out of a quality barrel, bench shot, controlled conditions. AAC is pretty inconsistent ammunition as well, and unless that's a relatively slow twist barrel, like 1:9 or slower, will likely not stabilize well enough to group well.

FMJ and especially M855 suck for accuracy. Until you test match grade ammo, you will never know how good or bad your barrels is.

It's a BA 14.5 with 1:7 twist rate, 5.56 chamber. BCM Mod 1 compensator.

The 1:7 twist isn't going to serve your 55 grain ammunition well at all. 1:9 - 1:12 seems to be the sweet spot there.

Winchester Valor M855 isn't going to get you the groups you seek. Don't get me wrong. I have plenty of it in my horde. It's plenty accurate to MOBG and does the job, but isn't going to give you any  idea of what the barrel is capable of.

Grab a box or two of quality, match grade 5.56 and a good sled or bench rest with a bag. 5 shot groups and see what you come up with. Stick with > 62 grain... I'd go with 77 grain with a 1:7 twist barrel. That will give you the best idea of what the rifle will do. It doesn't limit what ammunition you can shoot with it but you have to expect that a poorly matched round will also poorly perform.

If you want to remain somewhat consistent, after confirmation of an adequate barrel, pick a bullet weight and stick with it. I shoot a lot of 855. My HD mags are usually loaded with Xtac. Range drills I'll run whatever as it's more about repeating fundamentals and target acquisition than precision.

If I need to be precise, I keep a few boxes of Hornady 62 Frontier and TSX on hand that I go to for precision (I sighted to and occasionally confirm with the TSX). Everything else I shoot groups within an inch or two at 100 of my zero, albeit not always a fantastic group as, they're not always fantastic rounds.

Check to see if your barrel is loose… check by separating the upper receiver assembly from the lower,,, hold the upper receiver in one hand and with the other hand grab the end of the barrel, twist your hands in opposite directions feeling for any movement between the barrel and receiver.

If loose retighten your barrel, re-zero and enjoy your smallest groups.

Hopefully it’s that simple for you.

Best of luck,

Respectfully
Shootsenmeister

1/7 twist is every bit as accurate with 55 grain FMJ's as 1/9 or 1/12. The bullet is the problem, not the twist rate.

Agreed. Like the majority of 5.56 barrels, my ARs have both 1:8 and 1:7 twist. They shoot 55 grain pills just as well as 62 or 69s.

I have given my 55 grain hand loads to several people over the years that were having trouble sighting in a new gun because of ammo. Without fail, consistent ammo allowed them to complete their sight-in. Never once asked what the twist was on their barrels.

Mil-spec 5.56 ammo is not known for accuracy. It is made to be reliable when conditions are less than ideal.

If you do not reload, then it would be a good idea to purchase some match grade .223 ammunition for sight-in. Once the sights and optics are set, then go to the 5.56 ammo to see what you have. In most cases, the .223 and 5.56 trajectory will be almost identical. A slight elevation adjustment may be need if you intend to use 5.56 exclusively in the particular gun.

In my experience, 5.56 groups are never smaller. If you have a 1 MOA rifle and get 3 MOA with mil-spec ammo, you are doing well, indeed. If you find a brand your rifle likes, buy a lot of it.

That's patently untrue. 55 grain m193 shoots "fine" from a 1/7 twist barrel  but not every bit as accurately as it does in a slower twist barrel. Using Berger's ballistics analysis,  m193 is optimally stabilized at 1/11. It's BC is matched at around 1/9, meaning beyond that, it's over stabilized and performance will degrade. At the very best, 55 grain is at the razor's edge of the 1/7 twist range and not optimal.

Physics doesn't lie.

If the OP wants to find out if he has a decent barrel, he needs a decent ammunition that suits his barrel.

My best groups from 1/7 twist barrels come from 52/53 grain match bullets, almost always under 1 moa for ten shots at 100 yards. FMJ's are crap as far as accuracy is concerned. M855 even worse.  

We aren't shooting bench rest rifles which are usually setup up with a twist rate that barely stabilizes their bullets. There is no such thing as "over stabilized" unless you shoot something like Hornady's lightest .224" super explosive varmint bullets that have a very thin jacket.

I relegate 1/12 and 1/9 AR barrels to blasting service, they offer me nothing of value otherwise. I own a Colt 16" H-Bar with a 1/9 that is a hammer, with any match grade bullet, it's a dog, just like every other rifle I own when it comes to military clone ammo. 3.5" is common with FMJ's, sometimes worse.

Without seeing the OP's bench setup and technique I would say his rifle is disappointing, but without trying really good ammo we can never know. The muzzle device is suspect as well.

Over stabilization is a product of spin rate and BC. A bullet with a poor BC is extremely easy to over  stabilize... essentially spin it so fast you accentuate its flaws. M193 has a BC of ~.243, which is abominable. It might seem like a misnomer but it is a real thing. If it wasn't, every barrel would have the same twist rate because more spin would always be better.

But to the point, I get MOA from my 16" BA middy so I know it's possible. I also built it myself and have skills and tools. I don't get that with M855. Some of it shoots better than others. It takes good ammunition.

I got rid of my "A1" and all of my m193 because I found it shot considerably worse in my fast twist barrels than M855 and I didn't care to keep up with so many choices. Since then, I haven't had any interest in slow twist 5.56.

Thank you.

It is not necessarily the bullet weight that determines the best twist rate to use, but the length and shape. All 55 grain pills are not created equal!

Very true, but aren't we discussing the M193 the OP was firing? If the question is one of barrel accuracy, it seems like the answer would be to shoot a quality round that matches the twist of the barrel. Anything  else is at best a gamble because it's less likely to shoot well than a round that IS well suited to the barrel twist. If the question was "what bullets can my barrel shoot accurately", well, that's an endless list and exceptionally subjective.