.308 Bolt or Bolt carrier affect on accuracy

[M25BeastShooter]

Anyone have any experience with accuracy being affected by bolts or the bolt carrier on a .308 AR?

I've been building a .308 AR DPMS format. I used a high end Kreiger 1:11 barrel, DPMS upper a DPMS bolt/bolt carrier. Couldn't get it to regularly hold better than 1-2 moa using any match or hand loads.


Switched uppers to a SI Defense upper, a new SS 1:11 barrel (both 24") same bolt bolt carrier.

The rifle routinely stove pipes. When it does, usually that shot is a wide flier.

Switched bolt carriers groups doubled in size, and one went total vertical stringing like a cartoon machine gun blast.

I've got a JP enhanced bolt in bound hopefully that will cure both the ejection and accuracy problems.

This rifle is driving me crazy. Oh it's not me as my Rock River LAR-8A4 with a std 20" barrel routinely shoots between .55 and .75. All my groups are 5 shots

ANY HELP?

 

[picone]

Re: .308 Bolt or Bolt carrier affect on accuracy

I got the exact same barrel in 26" and having the same problem (accuracy) only more like 4-6MOA. I tracked "a" problem to the handgaurd hitting the gas block during fire. The mfg took good care of me on the handguard and hopefully be able to shoot it again in a week or two. Hopefully this will be my only problem.

Post a picture of your rifle if you don't mind.

 

[ssgp2]

Re: .308 Bolt or Bolt carrier affect on accuracy

I have a DPMS LR308 and a 260Rem upper.

I can switch bolt+carrier from one upper to the other without change in accuracy.
Sub MOA

 

[pagana]

Re: .308 Bolt or Bolt carrier affect on accuracy

There are a number of items relating to BCGs that can affect accuracy. If 2 carriers from the same Mfr were tried with no effect, 1st see if the gas tube is noticeably binding with the carrier key as the assembly is coming into battery. Do this with the upper off the lower as the spring force makes feeling anything difficult. This normally will produce vertical, but only if the upper was assembled properly and the gas tube is free to float, i.e. if the tube is biased by the barrel nut then it can affect accuracy in the way described. The other items to look for have to do with proper timing and headspace as well as fit of extension and upper receiver, as well as whether or not the carrier is itself coming to rest against the extension or the cam pin is stopping the assembly. Point is, start with the easy one described 1st then move on to the others.

 

[M25BeastShooter]

Re: .308 Bolt or Bolt carrier affect on accuracy

Just pulled the bolt out after today's shooting and micd the lugs they ran .314, .314, .312, .311, .309, .310, .308

Not sure if these variances are enough to matter but it seems like a place to start.

I checked the gas tube it's free floated all the way into the reciever and has plenty of movement to align with the gas key. The gas key doesn't seem to be sticking.