Bolt action & AR semiautomatic pressure limits COW

[SDguy]

OK I expect this has already been discussed though the Advent of the 6mm ARC & the 22 ARC injects a why view point. We can see the 6mm arc was released with separate Gas & Bolt gun max pressure limits. Seems the 22 ARC will be similar. Yet the 6.5 grendel was released with a single pressure limit to be applied to both Gas guns & bolt action firearms.

Why is a bolt action 6mm ARC load allowed to run higher pressure limits than a bolt action 6.5 Grendel load? Expect the same question will apply to 22 ARC vs 6.5 Grendel when the data is out.

[SDguy]

Tried & true sane 6mm PPC bolt gun data max pressure 58,800 PSI.

Tried & true sane 6.5mm Grendel Gas gun 52,000 good bolt & brass life.

6.5 Grendel bolt gun font= 52,000 good brass life.

Commonly proven 6mm ARC gas gun 52,000 good brass life.

Perhaps a bit high 6mm ARC bolt gun 62,000 Primer pocket & brass life may suffer.

22 ARC gas gun ?

22 ARC bolt gun ?

[LRRPF52]

In practice, you only see about 100fps increase in performance, which means almost nothing downrange.

For the bolt guns, you get a little bit more room at the top to find accurate loads that are at the upper ends of velocity, but nothing to write home about.

The more effective variables for generating higher velocities are:

1. Barrel length
2. Optimum powder selection
3. Increased COL for more usable powder volume without increasing chamber pressure

I’m a fan of using optimum powders at lower chamber pressures for long brass life. It’s a best of both worlds when looking at performance and component life.

For me in the Grendel, 31.2gr of CFE223 under a 123gr cup and core bullet works great towards those goals, which for me means a reliable steel plate-punching load mainly for fun out to 1000yds at higher altitudes.

My Lapua and Hornady brass eject looking new. I’ve never seen a loose primer pocket with that load so far.

I do shoot a lot of factory ammo though nowadays.

[Fess]

Why is a bolt action 6mm ARC load allowed to run higher pressure limits than a bolt action 6.5 Grendel load? Expect the same question will apply to 22 ARC vs 6.5 Grendel when the data is out.

The reason has to do with the bolt strength. The Grendel was essentially based on a variant of the 6mm PPC case with the shoulder blown foreword (one of the developers, Arne Brennan referred to it as the PPCX case). The PPC is typically run above 60Kpsi. The issue is that the Grendels developers decided to design around the AR15 platform with minimal modifications and not develop a different bolt and barrel extension that could deal with higher thrust levels.* The thrust against the bolt is the (max internal case dia) x (max chamber pressure). The bolt was designed for the 5.56x45 with a case dia of .376". The Grendel/ ARC case is .441" dia. That meant reducing the max chamber pressure to avoid bolt breakage. Since the Grendel was going to be limited to 52,000psi anyway, the original Lapua case was designed with relatively thin case walls near the base to maximize propellant volume. If the pressures get too high or extraction starts before the chamber pressure has dropped enough, the case bulges and you can get the "Dreaded Grendel Belted Magnum".

*Beefed up AR15 bolt/extensions do exist. CMMG uses the oversized"powerbolt" on the Resolute MK47, Colt did with the the CK901 in 7.62x39 for Yemen, Remington for the 30 Rem AR, DTech still makes them for WSSM AR15's.

[kmon]

The Grendel was introduced in the ar-15 and factory bolt actions for it came years later. Hornady has done a little load information for the Grendel but very little since its introduction other than for new bullets. I suspect with the ARC cartridges since there are bolt action rifles that will be chambered in them go ahead and do the data for bolt actions with those cartridges of their design.

Some of us that really like bolt guns for hunting and also like the Grendel screwed barrels on rifles for the 7.62x39 mine being a CZ. It might take a while to find but there have been a few threads about loading for bolt actions and If I remember correctly one that Bill Alexander said the original Lapua brass was specked for 58,000psi and could be safely loaded to that but you will have much longer brass life at the <52,000psi loads for the AR.

Like pointed out in above posts you gain some velocity but not really that much from the extra, the shooting I do with the Grendel the loads in the 50kpsi range are fine. Plenty for shooting targets to 600 yards and game like deer , hogs and coyotes to 400 or a little beyond. If I want longer range with the 6.5s I will just reach further back in the safe and get the 6.5-284 or 264Win Mag, or for grins and shorter range 6.5 hunting the open sighted 1903 MS in its original chambering 6.5X54.

[gldprimr]

I’ve had such success with the Grendel in my CZ-527 that it’s really all I use for hunting now. If I was going on a hunt where truly long range shots requiring greater velocity were expected I’d rather use another cartridge with greater powder capacity than hot rod the Grendel. For all the deer hunting I do where I live however the Grendel has proven to be more than sufficient.

[Harpoon1]

Why is a bolt action 6mm ARC load allowed to run higher pressure limits than a bolt action 6.5 Grendel load?

It’s doesn’t! The difference is Hornady provided data for bolt action rifles too, while Alexander Arms, who developed the Grendel, didn’t!