6.5 Grendel Barrel Length Comparison

[LRRPF52]

This is a great graphic, and really points out the remarkable aspect of the 6.5 Grendel in shorter length BBL's. In my own usage and assessments, I run 6.5 Grendel in AR15's. And with that, 20" is about as long as typical. And when looking at the velocity loss from a 20" down to a 14.5" BBL, it's remarkably less than you might think. Dropping only about 100 FPS. Which no doubt is why 12.5" is so popular, because that's probably right about where the inflection point is, where further cuts start getting expensive. And with that, Grendel impact energy out of a 14.5 (or 12") is remarkably good out to very practical distances. It's one of the cooler aspects of this round.

From a logic standpoint, this makes more sense the more I learn. The best way I can figure it: after about 3" of travel, most of the powder is burned, and only a little more additional gas is generated. That peak pressure and volume in the casing and little bit of barrel, is basically the "bottle" of high pressure gas that's pushing the bullet the rest of the way down the barrel. with just a little extra gas generation from additional burn.

In 6.5 Creedmoor, it's a big reservoir bottle, so can keep pushing down a longer barrel. In 6.5 Grendel, it's a shorter little casing, and so a smaller little bottle. Meaning additional barrel length doesn't buy you as much, as there's less gas in a bottle to keep pushing it. In the most extreme case, I recently discovered, of .22LR, where the gas bottle is a straight walled little .22 Casing of quite small volume, additional barrel buys you very little. I recently SBR'd an 18" .22LR BBL down to just 13", with ZERO velocity loss with 40 gr bullets (within stnd dev.), due to this. Anyway maybe everyone else recognizes that, but to me, it helps explain while shortening the barrel in a 6.5 Grendel isn't all that expensive; compared to .223, which is higher pressure and has a large bottle volume ratio compared to the bullet and barrel diameter.

Grendel is a very cool little round.

From shooter perspective, I just don’t notice much difference between 12”, 16”, and 18” Grendels. I can show you the minutiae with a ballistics program of how they differ, but when I’m in the scope, I break the shot and watch the round go-in just the same.

That little 12” cranks the Federal 120gr SMK OTM load out at 2400fps, so there really isn’t much difference between that and the 18” with the same load doing 2500fps.

I can have suppressed and about the same ballistics for less overall length, in a compact little blaster that doubles as a great HD and hunting system, while still staying very lightweight and maneuverable.

I can’t spot my own hits with a 6.5 Creedmoor or .260 Rem as easily because the sight picture comes off-target pretty noticeably, unless I use an offensive muzzle brake.

There are a lot of penalties I have to pay stepping up to the 6.5-08 class of cartridges, especially in a gas gun.

For bolt guns, if someone is going that route, the 6.5 PRC out-classes the .260 Rem and 6.5CM substantially. 143gr going 2950fps from a 22” barrel is no joke.

The short, fat powder columns with a balanced overbore ratio are really efficient at generating velocity, and I can’t think of any that really do what 6.5 Grendel does, especially with its 50,000psi chamber pressure.