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

[rickt300]

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?

[VASCAR2]

[Red*Lion]

Check out KAK's AR offerings in 7.62x39. They design their components such as their BCG's to be exceptionally sturdy. You will not have bolt issues with KAK products. I get around 1.5 moa with my 11" AR in 7.62x39 using a KAK bcg and barrel shooting steel cased Russian ammo.

https://www.kakindustry.com/

[lazyengineer]

Lower P round. So more forgiving

[rickt300]

Lower P round. So more forgiving

Probably it, I have seen only one bolt ever broken and it was a 6.5 Grendel.

[StoneHendge]

The 7.62x39 bolts do go through extractors like Joe Biden goes through pudding cups.

[BluntForceTrauma]

From KAK's website for their 7.62x39 bolt: "THE EXTRACTOR IS CONSIDERED A WEAR ITEM AND IS NOT COVERED AFTER SHOOTING."

[Fess]

As VASCAR2 noted, the rim on the 7.62x39 and Grendel cases is thicker than on .223, so that is a big reason that Bill Alexander deepened the bolt face a little. It allows more meat on the extractor. As near as I can tell, early 7.62x39 AR's made as few changes to the standard AR15 as possible, so they kept the standard bolt face depth. For a long time, 7.62x39 AR's were not common, so there was not a big effort to optimize their bolts. By the time 7.62x39 AR's became popular, the 0.125" deep bolt face was the "standard" and it looks like noone wanted to buck the trend. They mostly shot factory ammo anyway, so there was not a lot of people handloading higher-pressure rounds. It is important to note that when Colt made a 7.62x39 version of the AR (CK901) for Yemen's military, however, they used an oversized bolt and extension for durability.

When Bill Alexander developed the Grendel, he was trying to squeak out maximum performance from the AR platform without changing the bolt diameter and barrel extension. This led to optimizing the bolt over what was already available. If I remember correctly, one improvement that Bill Alexander made on his Grendel bolts was to increase the radius of the transition from the bolt face to the lugs (inside the bolt). He mentioned that there were others improvements, but I don't recall specifics. There are various other improvements that have been made to AR-type bolts that are not Grendel-specific. One of the most common is to increase the radius of the fillets at the base of the lugs.

I know that KAK has done a lot of work on bolts but I don't know how much of that has carried over to their 7.62x39 variant. Heck, their E3 bolt for AR's is sufficiently different that it requires its own special barrel extension.

[BluntForceTrauma]

Fess, KAK is a different company than KAC.

[Fess]

Oops, I need to pay more attention.

[Red*Lion]

From KAK's website for their 7.62x39 bolt: "THE EXTRACTOR IS CONSIDERED A WEAR ITEM AND IS NOT COVERED AFTER SHOOTING."

Extractors are wear items on all AR calibers.

[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?

[rickt300]

Interesting there LRRPF52, So the right thing to do is use a Grendel bolt. Seems it would be hard to find a barrel headspaced to match.

[LRRPF52]

Interesting there LRRPF52, So the right thing to do is use a Grendel bolt. Seems it would be hard to find a barrel headspaced to match.

If I was putting together a 7.62x39 AR-15 barrel and bolt, I would start with a JP Grendel bolt and have the barrel chambered to that.

Otherwise, invest in a lot of replacement extractors or entire bolt assemblies.

Another problem is the inconsistency of steel cased 7.62x39 ammunition.

AKs have so much slop and over-gas that they run really hard to deal with that (huge gas ports).

[chic]

So, if I understand correctly, use a Grendel bolt and cut 0.011" off the barrel?