AR-15 Upper Quick Fixes: Match Bolt Carriers

If you want an accurate rifle, don’t leave a lot of front/back bolt play (keep it .003″ but no more than .005″). Factory rifles run .012″ to .015″ play, which is OK if you need to leave room for dirt and grime in a military or field application. However, that amount of play is not ideal for a high-accuracy AR build. A lot of front/back bolt play allows rounds to be hammered into the chamber and actually re-formed in a non-consistent way, as they are loaded into the chamber.

The bolt affects accuracy in an AR-15 more than the carrier group. To get the most accuracy, the bolt and barrel have to be machined so that the headspacing is optimal when the round is chambered and the bolt locked. That is why if one orders a match-grade barrel for an AR-15 either the barrel comes with a bolt, the barrel manufacturer requires you to send in your bolt (prior to machining the barrel you’ve ordered), or the manufacturer requires you to send dimensions from your bolt.

The best accuracy usually comes from the bearing surface of the bullet nearly touching the rifling. Having the bullet jump any significant distance to the rifling tends to negatively affect accuracy. This is true in any rifle, not just the AR-15.

In addition to the above, you will want to keep the chamber, barrel extension, and carrier assembly clean to help insure consistent bolt lock ups critical to accuracy. You will also want to occasionally apply lube directly to bolt rings during shooting sessions.

Carrier key staking is also mentioned in the article. Young Manufacturing does not stake their carrier keys. “There has been a lot of talk about the pros and cons of staking the gas key on the carrier. Here is our opinion and why Young Manufacturing will not stake keys. We have been making carriers since 1991. The US Mil Spec. assembly drawing requires the carrier key to be staked. Contrary to some popular opinions staking does not SEAL the gas key. Staking keeps the screws from backing out Period. If you do not properly torque the screws to 56 inch pounds you will be staking a screw that is loose or one that is over torqued and prone to breakage.” Not sure how I fell about that, for me, a staked key is the only way to go. Something just does not feel right about it not being staked.

REFS:
http://bulletin.accurateshooter.com/2015/05/what-makes-an-ar-accurate-whitley-offers-answers/

Staking the gas key on the AR-15 and M-16 carrier.