05-24-2013, 09:13 PM
Roger that on 7mm being too heavy for weight/BC advantage.
I was talking with Lapua's R&D team, and they have run the Grendel case 15% higher than .300 Win Mag pressures in a Sako bolt gun. Brass is ruined, but never failed. The more I deal with it, the more I like the fact that the Grendel runs at a lower pressure than 5.56 or 7.62, because it really doesn't need it.
As I run my DM Courses and compare my 16" Grendel against 77gr Mk.262 from 18" guns, there are very clear differences in performance between the two as far as wind-drift and retained energy goes. A sub-1/2 MOA capable 5.56 has less chance of a hit at distance than my ~1 MOA Grendel. You know when you hit a steel plate with the 123gr from the Grendel out to 600yds. Even with 77gr 5.56 at 2820fps mv, it's very difficult to register hits past 400yds, especially with a tailwind. The BC of the 77gr SMK leaves a lot to be desired.
![[Image: SDC12590_zps4de19bf6.jpg]](http://i1085.photobucket.com/albums/j422/LRRPF52/SDC12590_zps4de19bf6.jpg)
Any case with a .473" head diameter takes it out of the Assault Rifle Intermediate Cartridge Category from a soldier's load & mag capacity perspective (unless we rewind the clock to the pre-1950 era with the .276 Pedersen & 7.92x33 Kurz), but does introduce interesting possibilities for the hunter and competitor, who will be mostly using magazines of no more than 5 or 10rd capacity.
I saw your mention of .270AR on your site. Are you setting the shoulder back as well, or just trimming the neck? Any pics of a loaded cartridge?
ETA: Just found most of my answer:
Quote:One thing, the Grendel/Lapua cases will not handle more pressure than a 6.8 SSA/Hornady case...
I was talking with Lapua's R&D team, and they have run the Grendel case 15% higher than .300 Win Mag pressures in a Sako bolt gun. Brass is ruined, but never failed. The more I deal with it, the more I like the fact that the Grendel runs at a lower pressure than 5.56 or 7.62, because it really doesn't need it.
As I run my DM Courses and compare my 16" Grendel against 77gr Mk.262 from 18" guns, there are very clear differences in performance between the two as far as wind-drift and retained energy goes. A sub-1/2 MOA capable 5.56 has less chance of a hit at distance than my ~1 MOA Grendel. You know when you hit a steel plate with the 123gr from the Grendel out to 600yds. Even with 77gr 5.56 at 2820fps mv, it's very difficult to register hits past 400yds, especially with a tailwind. The BC of the 77gr SMK leaves a lot to be desired.
Any case with a .473" head diameter takes it out of the Assault Rifle Intermediate Cartridge Category from a soldier's load & mag capacity perspective (unless we rewind the clock to the pre-1950 era with the .276 Pedersen & 7.92x33 Kurz), but does introduce interesting possibilities for the hunter and competitor, who will be mostly using magazines of no more than 5 or 10rd capacity.
I saw your mention of .270AR on your site. Are you setting the shoulder back as well, or just trimming the neck? Any pics of a loaded cartridge?
ETA: Just found most of my answer:
Quote:I took a 6.5x47 case and pushed the shoulder back .120 then necked it up to .277. It has a little more case capacity than a BRX and using the 6.5x47 case no fire-forming is needed.
Early testing shows out of an 18" barrel, using CFE223 powder 120gr bullets will hit 2850, 130gr Bergers 2700fps . 8208 pushed the 130 Bergers to 2788fps at the max load of 36gr.
The exterior ballistics of that 130 load beat the 308 M118 load and it runs right with the 308 shooting 155gr Lapuas so even though it was intended as a larger AR15 hunting cartridge it should hold it's own at long range target too.