bushmaster agrivation

M

mmercy

Guest
Am fighting with a bushmaster varminter 24" stainless barrel,rifle prints 2 distinct groups,have tried 4 scopes a multitude of 55-69 gr factory and hand loads,rifle was sent back to bushmaster barrel was supposedly replaced still shoots virtually the same,have installed boss type tuner /muzzle brake,groups range from 5/8"-1 1/2" with most dispersion in the horizontal but always 2 distinct groups,have tried shimming upper and lower,no change am losing my sense of humor with this one,any input would be appreciated.
martin.
 
I feel your pain...

Let me first start out by saying this is not a smartass reply...
I am an AR-15 guru...
My brother owns LaRue Tactical.com ...
I used to shoot alot of Bushy rifles up until 10 years ago...
The Bushy Q/C has slipped a long way off track...
As a result of quality slipping and holes and tolerences not being held to tight enough specs...it is more difficult to get the rifles to group correctly...
Many...I repeat many AR-15 manuf. get their parts from the best/lowest bidder...which means holes all over the map...
The good AR-15 builders use there own machine shop...using CNC machine center from HAAS and OKUMA to build top notch AR-15 rifles that shoot tiny bugholes...
Do not believe for a min. that all of your testing and great reloads are the problem...parts not made correctly and tolerances all over the place lead to group stringing all over the target...
I know this is not the answer you want...
It could be the problem with your group stringing...
Thanks...colonel redfeather.
 
Martin,
Are you shooting from a magazine? If so is every other shot grouping together? Try single-loading and see if the problem goes away. If it does, there's your problem (you might want to try different mags), if not I'm stumped.
West
 
Thanks for the replies,
Redfeather,I think you have some valid points I'm not impressed with the fit up of parts,when I questioned BM about clearance between upper and lower (used .015" shims to take slop out) I was told that independant testing has shown no loss of accuracy due to loose fit between upper and lower and clearance was in spec,also to be fair BM did say we could return the rifle a second time and they would look at it again,not sure how they would react to the tuner/muzzle break.
West, am using both single shot mag and 10 round mags will try some experimenting on different mags,group separation is more pronounced when feeding from magazine,but horzontal dispersion is more pronounced when firing from single shot mag.
martin
 
Not a guru here by any means... but have you tried some good slippery lube (such as moly paste) on the cam pin / carrier, and maybe on the backs of the locking lugs? Your group problems could (!!??) be due to irregular bolt lockup, which happens if parts are "dry." I found this "cured" impact difference between first round and magazine fed subsequent rounds in a couple of guns.
I might be all wet here (not a guru as I said) but at least it would be real simple to try this.
 
Bushmaster AR

mmercy: Your posting caught my eye: have a BM CMP, through the Club purchase program, excellent except trigger had to be replaced at 1500 rds. when doubling (worn disconnector), but extremly accurate, as is an upper with a chrome-lined (go figure) 1-9, 20". Just grabbing at straws, but if you have not already tried it, a proven method for benchrest, with the AR, is to position the front rest/bag as close to the receiver as you can get it. I've tried it, and it works for me. "A ? of Bag Placement and Gun Design", by M.L.McPherson, "Precision Shooting", October 2001 issue. Another thought is your gas rings, if you are using the "issue" 3 split rings, are the gaps seperated? I got tired of keeping them seperated and switched all 4 uppers to the one piece McFarland ring. $3.60 each from Sinclair.
 
I've played around with and built quite a few AR's, and for the most part, the barrel and chamber is where the precision comes from (I'll add 'IMO'). This fall a friend brought in a Bushmaster varminter that he couldn't chamber certain rounds in and it shot very poorly. Found the chamber/throat was so far out of concentric with the bore the bullet was engraved by the lands on only one side, and that was with 50gr SP seated to correct OAL. I ran a piloted throater in to just clean it up. The chambering issue was solved and it shot OK, but I'm installing another barrel on it for him this winter.

I'm betting the barrel/chamber is the culprit. Of any AR's I've built with quality tubes (Lothar Walther, Shilen, Douglas, Krieger, etc...) I've never had a problem getting sub MOA from them, and most were closer to 1/2 MOA.

Now if your gun is shooting two distinct groups as you mentioned and both groups are on the small side, I'd look at your scope and mount, or the barrel nut. Often I'll take the barrel extension I'm going to use on the build and lap it into the front of the receiver by rotating it with compound. If you have a poor mating between the receiver and barrel extension/ or the torque isn't tight enough that barrel might be shifting in the upper receiver.

One more thought too. Check the gas tube and make sure it isn't bottoming out in the carrier key. That should never happen, but who knows ????

Hmm, I guess I could go on and on here....
 
Bushmaster

Fifteen years ago, Bushmaster was producing a fine AR-15 and variants. Sadly, the quality control went south a while ago. If the quality control goes south, tolerances get sloppy and start to 'stack', you are fighting a losing battle. Sell the Bushmaster and get a DPMS.

Lou Baccino
 
Thanks for the replies,think I have covered most of the bases and may conclude this rifle is more prone to shooting sub par rather than sub moa if by some chance I can make it shoot better than sub par I'll post results.
Thanks,martin
 
You did not say how you were shooting it. I once had a problem with a rifle that shot two groups and found my jaw muscle was torquing the stock sometimes when I shot. Also check the barrel nut. I have had several dept. colts that came loose. The gas tube should not hit the gas key. Remove the bolt and cycle the bolt carrier by hand upside down and look for any movement of the gas tube or felt resistance when gas tube enters the gas key. Slightly bend the gas tube to correct the problem. It could be your table manners too. How the rifle is recoiling can cause vertical group problems. Have you removed the rear sling loop? I made a homemade bag bar and improved the vertical dispersion a little on an f-class rifle. Good luck.
 
You must log in or register to reply here.
Back
Top