65G HLB Project

[BluntForceTrauma]

Gentlemen, Barbarians, and Members of The Horde:

I want to conduct an experiment and I need your help. I want to specify and test a 6.5 Grendel barrel to see if there's any way to increase velocities while keeping pressures within SAAMI 6.5 Grendel guidelines.

The 6.8 SPC II camp, for example, claims that this can be done in their cartridge with similar case capacity to the 6.5 Grendel, and after giving it some thought, I think it's at least worth exploring. There is no magic pixie dust that can be sprinkled on a cartridge to give it more velocity; either there are universal principles of physics and ballistics and metallurgy that can be applied to any cartridge or there is only marketing hype, wishful thinking, and gambling against the odds.

The 6.5 Grendel was founded on innovation and I want to see if there's room for more. For example, in their .50 Beowulf and 6.5 Grendel bolts, Alexander Arms pioneered the use of 9310 steel, something we hear quite a bit about these days. Whodathunk? And, of course, they were one of the first, if not THE first firearms manufacturer to specify a chamber with a compound, dual-angled throat.

But let's not stop there, let's see what else we can do.

And thus we have the 6.5 Grendel Handloader's Barrel (HLB) Project. I say "handloader's" because, even if successful, a barrel with the specifications I am about to discuss will only be useful to those handloaders who understand the risks inherent in maximizing its full potential.

There is much, much more to say in this thread, and I need some heavy-duty, rocket-scientist, ballistics theory-type contributions, but let's just cut to the chase:

Typical 6.5mm barrels are first bored with a minor diameter hole of 0.256". Then metal is removed from the bore creating the grooves (the major diameter) measuring 0.264" while leaving the lands at the bore diameter of 0.256".

The difference between the major and minor diameters is 0.008". Dividing that by two gives us a typical land height of 0.004". Note that the typical land height for .223 barrels is 0.025" and for 6mm barrels is 0.003". Are they driven any less hard than the 6.5s? Than the 6.5 Grendel? I want to test a 65G barrel with a land height of 0.003", which means I need a 6.5mm barrel first bored to 0.258".

Whatever force a 0.004" land imparts to engraving the bullet and thus to pressures is effectively reduced 25% by decreasing to 0.003". Right? My math doing OK? Now the force may, indeed, be minimal relative to the whole pressure calculus, but whatever the lands contribution may be, it is reduced by 25%.

So far, so good?

Next, a typical 6.5mm barrel (also, specifically, the 6.5 Grendel SAAMI minimum specification) has six lands. Let's take away three of them. (AccurateShooter.Com reports: "P. O. Ackley believed that, all things considered, a properly-made 3-groove barrel is optimal for most common calibers.") Anyway, we've now made a further 50% reduction in engraving force. So whatever force the rifling imparted to the pressure calculus has now been reduced 50% plus the previous 25% for a total 75% reduction.

Of course, I'm gonna need 5R-style lands, with something like a 45° ramp on each side. Shall we call it "3R" rifling?

My question: You guys know anyone who can make this experimental barrel? Don't just say, "Uh, these guys kinda make barrels . . . I think." I need, "Yes. This guy can do exactly what you want and here's his website."

Finally, we need input. We need to tear this apart from every angle. We already know that reducing the size of the lands just makes the rifling erode faster. If the bullets are launched too hot and heavy they could skid and not engage properly on less-aggressive rifling. Any other problems foreseen? Don't be afraid to play devil's advocate, but expect to be respectfully cross-examined. Let's wring this idea out. Don't want to waste cold, hard cash on a non-starter, hare-brained idea.