Military round comparisons

[woohoo]

(Tony Williams - who else?)

Absolutely right, Stan. Thank you for pointing that out. And the SF community is seriously interested in a weapon in a calibre that can deliver the associated benefits.

The Canadian paper study presented at Shrivenham last year showed just how effective the Grendel could be - when fired from a weapon with a 24" barrel. It has done much to re-ignite the calibre debate in military circles.

However, as soon as you fire the existing 6.5 Grendel from a weapon with a 16" barrel, retained energy levels drop-off alarmingly - to the point where the Grendel offers no appreciable difference versus 5.56 mm. This has been tested and validated by at least two mainstream manufacturers. (It may also explain why Dr. Gary Roberts gel tests were inconclusive). Hence my view that a slightly longer cartridge with increased powder capacity would easily overcome the problem and provide a true GPC round.

One of the other things I've been looking at is whether an extended version of the 6.8 mm Remington SPC case would be a better alternative to an extended Grendel case. While it would create a longer, more slender round, as LRRPF52 points out, the Grendel case can take more pressure. So, the 39 mm 11.3 mm case is the right one to extend IMO.

I like everything about the Grendel round except case length. A long case with a less pronounced shoulder would also facilitate easier feeding.

Murray's 7mm UIAC is more or less a Grendel extended. The Carcano is close too. He designed a bolt a little larger than my 800 series AR15 bolt but smaller than an AR10 bolt. I machined them for him last year. The problem I see with the 7mm bullets is the BC is low until the heavier weights are used then because of the weight they are slow with the case capacity what it is. One thing, the Grendel/Lapua cases will not handle more pressure than a 6.8 SSA/Hornady case...The Remington cases are junk. The larger diameter of the Grendel case extended will have more case capacity than the SPC case if the same caliber projectiles are used.
A .441 diameter case, 46mm long, 2.5" OAL of cartridge will have apx the same case capacity as my 270AR (based on the 6.5x47 shortened) 130gr Berger (BC of .496) hits close to 2800 from an 18" barrel in the AR15 platform. That velocity with a 123gr 6.5 or a 130gr .277 with respective BC will smoke a 308 even using Lapua 155s.
ETA- that velocity is close to 58,000psi, still 2700fps out of an 18" barrel is plenty to outperform a 308.