AR Accuracy Questions

I've been fighting an accuracy problem with my AR and have a couple of questions for those in the know. I put a CMMG 16" bull barrel upper on my Spikes lower in hopes of improving my groups for prairie dogs and other varmints. After many different handloads, factory ammo, way to many hours at the loading and shooting bench, I finally figure out two things. This barrel has a super short throat, I have to seat the bullets .030" to 035" deeper than the called for 2.250 that is standard, that is problem number one and for now I can work around it with hand loads. Problem number two is that the first round fed from the mag and the last one, or sometimes two, fed from the mag cause fliers. The first round flier is not to bad,.5 to .75", the last round flier can sometimes be an inch or more. So here's my question, what the heck can I do to get rid of this flier problem? This thing is about to drive me crazy!

Are you applying a light crimp? I've had fliers, but never from the same rounds out of the mag every time. What happens if you only half fill the mag?

Gravytrain,
Half full mag the first one is a flier and the last one is also. I don't crimp, but I have run several threw the rifle to make sure the neck tension is holding them and it is. No bullet setback or extension. Using TAC and seem to be getting good powder burn. I've been thru most of all that til my head hurts. I was shooting 3 rnd groups so I would just load 3 rnds. Well, if the 1st and the last of 3 are fliers it's hard to get a group doing it that way. Hard lesson learned. Now I load 2 extra and shoot the first and last into the dirt and getting pretty good groups. That and loading my bullets deep for the short throat problem.

Fire a 10 or 20 rnd group and see what it looks like

That is bad news! I cannot imagine what could cause it. There my be some gurus on here that can come up with some science.

I was going to try that this evening but ran out of time. I've shied away from the 10 rnd groups because of the other problems with the short throat, 10 rnds into a 3 inch group doen't tell me much, but now that I figured a couple of things out I need to see what a 10 rnd group looks like.

Have you tried a few different mags or loading single rounds? That is a real stumper man...

I tried single feeding a few days ago but that was before I discovered the throat problem and it didn't show me much. I had headed back out with a different Mag for a 10 rnd run but didn't make it. I've been using a Magpul PMag for all my testing and that could be the problem, but I hope not. I don't want a rifle that I have to use only certain mags to get it to shoot.

Have you tried a GO/NO-GO gauge on this chamber?

You are sure it is short chambered?

I hate to say it, but it may be psychosomatic, it's happening because your mind is anticipating it will happen.

You should get a friend to shoot 6 groups of 3 with a warm fouled barrel, 18 rounds in the magazine. Make sure they absolutely nothing about your suspicion.

Not a short chamber but a short throat. If I load 40 and 50grn Hornady's to 2.250 the bullet sticks in the rifling. Same for 55grn Dog Town bullets. But no I don't have a go/no go to try. Hey I was up in your part of the country the other day on my way to Gainsville cruising along 82.

I thought it might be a loose nut behind the trigger also, so I had my buddy try it with the same results.

How do you load your first round? Do you hit the bolt release and let it strip the round from the magazine or do you use the charging handle to chamber the round. I think hitting the bolt release should simulate the way the rest of the rounds are fed. I shot hipower for a few years and used the release to load the first round. Never crimped the bullet and never had an issue because of it. I would also try a different magazine.

I always use the bolt release, drilled into me in the Marines many years ago.

Man i hate to say this, but i don't have a clue what my magazines are, and i use cheap ammo. I would say my ar is one of the most accurate rifles i have ever shot. Put yours on a lead sled and see what you can get it to do! Some rifles are just more accurate than others. If it isn't grouping like you want after the led sled, sell it and get something else! I'm shooting a rock river with a 16 inch bull barrel and love it.

This is the reason quality control with ARs is what it is, and why you pay what you do to get controlled performance.


Not going to internet gunsmith it, but you don't need a bull barrel to shoot well.

Use factory loads till you figure out the problem. Use marked magazines so you know which is doing what. Don't add more variables.

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