03-15-2012, 08:44 PM
adamjp Wrote:The Grendel displays the characteristics that would make a solid cartridge for small arms, and a LMG on this line could be made a little lighter than the Minimi whilst still providing the volume needed.
I am not convinced that the Grendel is exactly the cartridge I would adopt. A little more taper in the case would be suitable, so possibly a case with a little more taper, but slightly longer (yes a little like the SPC). The opportunity exists to work out what you want to do, and then design the bullet to achieve that, and the cartidge to project it, and the rifles/LMGs to direct it. This is what the SPC folks tried to do, IMHO they chose to be constrained by currently available products and focussed narrowly on an SF requirement.
The Grendel would do fine loaded longer for a belt-fed, since it is a high pressure case. With a 130gr loaded long, more case capacity would be realized. The Grendel has quite a bit of case taper, it just isn't apparent since the case is so short. All that is needed is the right pressure to push a projectile as fast as is necessary. A 130gr needs to go only 2572fps to match a 147gr 7.62 for trajectory to 1000yds, however, it has significantly less drift, but has 400 ft-lbs less energy at the muzzle. By 900yds, it has exceeded the 7.62 for energy, and is really close from 500 on out.
[SIZE="4"]
7.62 NATO 147gr FMJBT 2750fps[/SIZE]
Code:
......Range Velocity Energy Trajectory TOF Drift
(yards) (fps) (ft-lb) (MILS) (sec) (MILS)
[COLOR="blue"] 0 2750 2468 0.00 0.0000 0.00
100 2530 2089 -0.00 0.1137 -0.23
200 2321 1758 -0.38 0.2375 -0.47
300 2122 1469 -1.11 0.3727 -0.74
400 1933 1219 -2.01 0.5209 -1.03
500 1755 1005 -3.07 0.6838[/COLOR] [color=darkorange] -1.35[/color]
[COLOR="darkorange"]600 1590 825 -4.30 0.8634 -1.70
700 1439 676 -5.72 1.0619 -2.08
800 1306 557 -7.38 1.2809 -2.50[/COLOR]
[COLOR="red"] 900 1194 465 -9.29 1.5214 -2.93
1000 1105 399 -11.51 1.7830 -3.39[/COLOR][SIZE="4"]6.5 Grendel LMG 130gr FMJBT .500 G1 BC 2572 fps[/SIZE]
Code:
......Range Velocity Energy Trajectory TOF Drift
(yards) (fps) (ft-lb) (MILS) (sec) (MILS)
[COLOR="blue"]0 2572 1909 0.00 0.0000 0.00
100 2396 1657 -0.00 0.1208 -0.21
200 2227 1431 -0.47 0.2507 -0.43
300 2065 1231 -1.27 0.3906 -0.66
400 1910 1053 -2.24 0.5417 -0.92[/COLOR]
[COLOR="darkorange"]500 1763 897 -3.36 0.7052 -1.19
600 1624 761 -4.62 0.8825 -1.49
700 1495 645 -6.04 1.0751 -1.81
800 1378 548 -7.65 1.2842 -2.15[/COLOR]
[COLOR="red"] 900 1273 468 -9.47 1.5109 -2.51
1000 1184 405 -11.52 1.7555 -2.88[/COLOR][SIZE="4"]6.5 Grendel LMG Lapua 144gr FMJBT .580 G1 BC 2500 fps[/SIZE]
Code:
......Range Velocity Energy Trajectory TOF Drift
(yards) (fps) (ft-lb) (MILS) (sec) (MILS)
[COLOR="blue"]0 2500 1998 0.00 0.0000 0.00
100 2350 1766 0.00 0.1237 -0.18
200 2206 1556 -0.50 0.2555 -0.38
300 2066 1365 -1.33 0.3960 -0.59
400 1932 1194 -2.31 0.5461 -0.81
500 1804 1041 -3.42 0.7068 -1.05[/COLOR]
[COLOR="darkorange"] 600 1682 904 -4.65 0.8790 -1.30
700 1566 784 -6.02 1.0639 -1.57
800 1459 680 -7.54 1.2624 -1.85
900 1360 591 -9.22 1.4755 -2.15
1000 1271 517 -11.09 1.7039 -2.47[/COLOR]Lapua lists their 144gr FMJBT at .636 G1 BC, but I think it's closer to .600, so I handicapped it to .580 just to illustrate the point.