7.62x39 bolts on new barrel

[Keep The Change]

I've searched the forum and the internet pertaining to the diffence in face depth between the 6.5 G and the 7.62x39.

I know the 6.5 G is deeper as Bill has designed and that would be my preference.
I have a Grendel on order at AA but I don't think I will have it before the barrel company needs it.

Would you guys just go ahead and get a 7.62x39 and have the barrel head spaced with that knowing that you will be stuck using the 7.2x39 bolt from then on?

Or would you wait patiently for the Grendel bolt?

I'm a llittle worried about replacement bolts in the future and getting my hands on a Grendel where as it should be easy to find 7.62x39 bolts or at least easier.

Is the draw back to the shallower face due to it causing extractor failures or shear problems?

[KentuckyBuddha]

I explicitly remember the Precision Firearms guy saying that the 7.62x39 bolt just plain won't work well. Thus the fact that he would not sell the grendel uppers he had that had with no bolt for fear the customer would put a 7.62x39 bolt in there and thus damage the perception of his brand. I might be putting words in his mouth and I apologize if I did, but I think that was the gist of a conversation we had at the peak of the gun-grabbing when there seemed a realistic threat to some of the continued legality of sales of AR platform rifles.

[Keep The Change]

That's kinda the conclusion I've come too. Bill did enough study of Colt's Sportster and testing himself that I should do it 6.5 Grendel all the way. It has a deeper face for a reason and 0.008" or whatever isn't a lot, but it must mean something, right?

I've talked myself into waiting and hoping my 6.5G bolt gets here in enough time for the barrel guys.

[LRRPF52]

Colt are the ones who developed the first AR15 chambered in 7.62x39, and they used a deeper bolt face so they could make an extractor with more material in the lip, since 7.62x39 has a much thicker rim than 5.56 does.

Alexander Arms picked up Colt's R&D and went from there, thus the deeper bolt face. Most other AR15 "manufacturers" use 7.62x39 bolts with the same bolt face recess as 5.56, and extractor breakage is a real issue, along with bolt fatigue.

[Drifter]

Reference this quote for info:

The change of 0.011" of depth of the bolt recess (3 sheets of writing paper) has significantly less bearing upon the life of the bolt than surface finish, let alone the geometry. What it will adversely effect is the extractor strength. The Grendel bolt design is not a simple opening up of the 5.56 bolt as typified by what is now referred to as the 7.62x39 bolt. The bolt is a balance of the extractor and the bolt geometry with the steel type used and the heat treatment. The pressure limit was set to 50,000 psi to provide a wide margin of error and also allow for an exceptional cyclic life. It also balances the recoil generated with weapon controllability in a platform weight conducive to the small platform the cartridge was intended to fit.

Link to source: http://www.rainierarms.com/?page=sho...product_id=545

[Keep The Change]

Thanks guys for the info and rehashing it for me. I was just tempted to go grab a 7.62x39 bolt and got to thinking about it again. I needed to re-convince myself that i just need to stick with the 6.5G bolt