Accuracy Issues w/ Carbon 15 Rifle?

I have a Professional Ordinance Carbon 15 rifle. I have had it for 6 or 7 years, but never been able to get it to shoot very accurate.
It will put 2,3 or 4 shots into a fairly tight group, then the next group will be in a 3 or 4 inch pattern. And this is at only 50 yards. Can't seem to find any rhyme or reason for the patterns either.
I have exchanged scopes, mounts, let the barrel cool, shot w/o the muzzle brake/suppressor, extra barrel cleaning, and tried different ammo. All the ammo I have shot has been 55 grain, but to me it doesn't seem like the type of issue to cause this big of groups.
I really don't think this is a shooter issue as I've shot some great groups with alot of other rifles.
I understand the design was bought and is still produced by Bushmaster. I contacted them and they no longer work on these rifles. Alot of the parts are gun specific and won't interchange w/ most AR's. There doesn't appear to be any parts available other than finding another rifle. The rifle functions and shoots great and at 4#'s it's very light and unique.
Bushmaster suggested that I could buy another bolt and barrel and try them. The bolt has rounded lugs on it and is slightly different than most Ar's. The barrel is think w/ fluting and I believe 1/9 twist chambered in 556.
Everything is tight and in good shape and I can't see where the gun has been shot alot. The receivers lock up tight.
One idea I had was to remove the barrel and retork it into place. Not sure what this would accomplish, but wanted to ask.
Any ideas?
Shane

Shane, no offense but, sell it. The Carbon 15 rifles were piles of shit then, and they still are now. Bushmaster has a reputation for making junk.

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Originally Posted by ShaneinWI

I understand the design was bought and is still produced by Bushmaster. I contacted them and they no longer work on these rifles.

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That says quite a bit.

Sell it and buy another AR... from a reputable manufacturer.

None taken. But I've never sold a gun and don't plan to start now. I just built (assembled) another AR and it shoots great. Shot nice little 1/2" groups last night. Is there anything I can do to help the accuracy of the Carbon rifle? Or is it just is what it is kind of thing?

Is it one of the barrels with the QD muzzle brake? If so, have you shot for group with the brake removed?

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Originally Posted by glocktogo

Is it one of the barrels with the QD muzzle brake? If so, have you shot for group with the brake removed?

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Originally Posted by ShaneinWI

...shot w/o the muzzle brake/suppressor...
Shane

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:cool:

Yes, it has the removable brake. I shot w/o it without any improvement. I talked to a guy at Bushmaster about designs who said that wasn't the best idea. Not sure why. The upper receiver has a slide on rail which attaches w/ a single screw. He said actually that is a good system. Bushmaster has improved the design to work the bugs out since Professional Ordinance built them. The design must have had advantages to some as they are still building the rifles.
The allen screw was alittle loose on mine so I drilled and tapped it for a larger screw which made things really tight.
The trigger was a full 10# pull before I had a smith clean it up to a clean 3 1/2#'s. Always thought that was the problem, but no.
I read somewhere that if x-rayed only the bolt and barrel show up as the rest of the rifle is carbon. Which is kind of neat, but not real usefull to us good guys.

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Originally Posted by Mr. Goodtimes

Shane, no offense but, sell it. The Carbon 15 rifles were piles of shit then, and they still are now. Bushmaster has a reputation for making junk.

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Agreed. Trying to wring accuracy out of the worst gun you could possibly get is a waste of effort.

Since you don't want to sell it, maybe you can change the barrel and BCG...

That's what Bushmaster suggested. But are the issues in the barrel or the carbon receiver design? Any advantage to removing and reinstalling the barrel? I have no idea if it's ever been off, but I doubt it's ever been messed with.

The receiver material or how the upper and lower fit together has absolutely no bearing on accuracy.

Are the bolt and barrel proprietary? If not, change them out - and not with something else from Bushmaster.

The bolt has more rounded lugs than a standard AR. So the bolt and barrel would have to be changed together. I'm sure the carbon handguard is unique so that too would have to go.
Does anyone know why I'm having such accuracy issues? The parts appear to have little to no wear and are clean, good condition etc. Was the stainless fluted barrel of poor quality to begin with? Maybe headspace is an issue to be checked.
Had it to the smith to tune the trigger, but didn't have him check anything else.

How many rounds do you have through the weapon?

Can you even put a standard barrel assembly on the weapon?

I dropped a BCM 16" midlength on my Carbon 15 lower. So far it's a tack driver.

I think tgace is the guy I need to talk with.
I assume you changed the bolt and the barrel? Handguard?
Were you having the same issues I am?
I haven't put that many rounds thru the rifle, but I bought it used.

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Originally Posted by Scorpion

The receiver material or how the upper and lower fit together has absolutely no bearing on accuracy

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Upper receiver material could impact accuracy.

The receiver itself? I wasn't talking about barrel material.

http://securityarms.com/20010315/gal...s/0500/534.htm

This is a photo of a rifle like mine.

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Originally Posted by ShaneinWI

I think tgace is the guy I need to talk with.
I assume you changed the bolt and the barrel? Handguard?
Were you having the same issues I am?
I haven't put that many rounds thru the rifle, but I bought it used.

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Well, I have a BM M4 flattop Carbon 15, not the older Prof Ord model so I don't know if it will work for you. I purchased a BCM upper with a BCM BCG and dropped it on.

Actually, the original upper was just as accurate. I just wanted the mid length upper. I will be building a new lower soon so I will have two rifles.

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Originally Posted by Scorpion

The receiver itself? I wasn't talking about barrel material.

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If the receiver flexes, accuracy could be affected. I don't know if this is the case with the rifle in question, but it is possible.

I also wonder if the rounded lugs are causing a poor lock-up.