I'm trying to avoid a problem

[ibgp3]

I have a Grendel AR, and a chance to get a 7.62x39 AR cheap, but without a bolt group.

Would I be good to go, or asking for trouble if I shared a bolt group between 2 different uppers?

[stokesrj]

As long as it headspaces within tolerance I wouold not hesitate.
Bob

[LRRPF52]

If it is one of these after-market 7.62x39 copycats using a 5.56 bolt face depth of .124", and you have an actual Grendel, then you can't sahre because of the Grendel's .135" bolt face depth, based on the original Colt bolt face for 7.62x39 made in the late 1980's.

Some have argued that running a bolt through different barrel extensions is a bad idea, since each will have its own shock pattern, which could lead to early fatigue of the bolt. I personally use dedicated bolts for each barrel, and recommend the same.

7.62x39 AR's are a handful if not built correctly, and encounter numerous functioning problems often with parts kist of cheap price points. Even some of the higher-end one require substantial trouble-shooting, namely firing pin mods, magazine mods, feed ramp tweaks, gas system tweaks, and buffer changes.

[samalama76]

Get Both!

I would definitely get each their own bolt and be done with it. It will put your mind at ease and you can get a "KIES" 7.62x39 complete bolt for $40 at joebob's!

Good luck!

[ibgp3]

Since many said get each it's own bolt, I lost interest in the 7.62x39.

I bought a 300BLK, with it's own BCG.

I just noticed that Tastyca is in Cuba! How do you do backatcha.
Do you have a Grendel, or an AK?

[Grimmy]

I would get a dedicated bolt if the upper is a deal. If not I would save your money and buy a 300 blackout. I've had both in ar's and don't regret selling the 7.62x39. The 300 offers more options from sonic to subsonic.