Need Real-World 7.62x39 Case Rim Dims

[BluntForceTrauma]

KSW, we fought many a long and bitter battle to try and preserve 0.136 as a standard, not because those are magical numerals but because it represented a stronger and improved bolt over what was currently available. Conceding that a 6.5 Grendel case in an AR15 bolt necessarily weakens the bolt compared to a standard 5.56 bolt, everyone's goal was to make 65G bolts as strong as possible. Bill A's engineering said the extractor claw or hook becomes too weak in a 0.125 Grendel bolt for long-term reliable extraction. It was counter-argued, however, that deepening the boltface to 0.136 created a new problem by weakening the lug support versus 0.125.

So, what to do?

Keep the lug support and weaken the extractor, or keep the extractor and weaken the lugs? Through some truly clever engineering, Bill A. believed he had found a good compromise, and it has served us well.

But innovation cannot be stagnant.

My goal is the same as the original goal: Make Grendel bolts as strong as possible.

Why not get more strength back if we can get it?

We can.

I've got the first round of CAD drawings for the bolt body back from my manufacturer and they are working on the extractor drawings.

We've been in these trenches a long time, and Grendel deserves the victory it is now achieving. But not gonna rest on our laurels. (As you probably know, I've also been working on bullets — for example, got "Valkyrie-killer" bullet designs needing manufacture: 104gr in solid copper has a calculated G1 BC of 0.550 at Mach 2.5 or 2,790 fps, and a jacketed lead version depends on the amount of lead fill but the 132gr version has a 0.670 G1 BC at Mach 2 or 2,232 fps.)

Anyway . . . bolts.

It can be reasonably argued: You fought so hard for a standard, why muddy the waters now?

We fought so hard for a standard because we didn't want the Grendel program saddled with weaker bolts and a reputation for breaking bolts and we didn't want this new cartridge saddled with the chaos of competing standards in a dimensional free-for-all. It was Bill A.'s fear that such a situation would inhibit SAAMI adoption. Thankfully, we are way past all those early concerns and they are moot at this point.

So, to me, that argues for continually improving the strength of Grendel bolts, which is what I intend to do.

Currently, there are plenty of both Mk136 and Mk125 bolts available, so barrels can be headspaced for whichever the customer prefers and corresponding bolts will always be available for both new and currently owned barrels.

My plan is to offer Mk125 bolts for members at the same great price, and I will also be moving my barrels to Mk125 pending successful testing of this new bolt. These wheels grind slowly, though, so that is many months out.

Having said all that, KSW, I'm interested in hearing your thoughts about Mk136 vs Mk125, as you mentioned above?