Do the 7.62x39 AR15's have bolt head issues?

[LRRPF52]

Why has the 6.5 Grendel bolt head been improved and the 7.62x39 still uses the original design? Is there some reason the improvement is not needed for the Russian round?

Colt did full engineering analysis and testing on 7.62x39 in their AR-15s, which was well-funded.



Bill A. spent time tracking down one of those project engineers to see what insights they learned from the 7.62x39 AR-15 program when he was doing his due diligence for the .50 Beowulf (which uses a rebated 7.62x39 case head), and they did a lot of things differently.

A few Hi-power shooters immediately started taking Colt 7.62x39 Bolts and chambered their tube gun AR-15s in PPC-based wildcats.




The after-market just assumed that you could make AR-15 bolts with the wider bolt face for 7.62x39, ream them to 7.62x39, and crank out rifles and parts with a cheap magazine to support it.

Their understanding and familiarity with 7.62x39 was so lacking, many of them used .308” groove barrels, totally unaware that Russian 7.62mm is actually .311”.

The after-market imitation 7.62x39 AR-15 rifles and parts were such an abortion, you had all these combinations creating excess chamber pressure, bolt thrust, and bolt torsion with really weak extractor lips.



Broken bolts and extractors became the norm.



To do 7.62x39 correctly, you really need to start with a proper 6.5 Grendel bolt + extractor and have your headspace set-up based off of that.

The .125” face depth bolts are a recipe for extractor failure for the same reasons they are with any other .444” case head in the AR-15.

You also have to really manage the gas system into the window of where reliability and durability find a happy trade-off, which is hard to do with Russian steel case ammo and its inconsistencies.

The reason is that heavy-gassed operating systems cause early rotation of the bolt while under partial load, which is harsh on the lugs and the extractor.

But heavily-gassed operating systems have more reliable primary extraction and full retraction of the BCG with inconsistent charge weights.