Military round comparisons

[LRRPF52]

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 is incorrect. I have a 16" Grendel, and it has produced 24" velocities with certain factory ammunition. Even at pressures under 50,000 psi, the 16" Grendel is no joke, sir. It does not drop off alarmingly from a 24" barrel, velocity-wise. You're looking at 18fps average difference per inch of barrel loss from a 24".

16" Grendel with Current Civilian 123gr Target Load at 2450fps

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Range Velocity Energy Trajectory TOF Drift (yards) (fps) (ft-lb) (MILS) (sec) (MILS) 0 2450 1639 0.00 0.0000 0.00 50 2357 1517 -0.32 0.0624 -0.12 100 2266 1402 -0.00 0.1273 -0.24 150 2177 1294 -0.21 0.1949 -0.37 200 2090 1192 -0.57 0.2652 -0.50 250 2004 1097 -1.00 0.3385 -0.63 300 1921 1008 -1.50 0.4149 -0.78 350 1839 924 -2.03 0.4947 -0.93 400 1760 846 -2.62 0.5781 -1.08 450 1681 772 -3.24 0.6653 -1.24 500 1605 703 -3.91 0.7566 -1.41 550 1529 639 -4.63 0.8523 -1.59 [B]600 1456 579 -5.41 0.9528 -1.78[/B] 650 1384 523 -6.23 1.0585 -1.98 700 1314 472 -7.12 1.1698 -2.19 750 1246 424 -8.08 1.2870 -2.40 800 1181 381 -9.12 1.4107 -2.64 850 1120 343 -10.23 1.5412 -2.88 900 1074 315 -11.44 1.6782 -3.13 950 1045 298 -12.73 1.8200 -3.38 1000 1020 284 -14.12 1.9654 -3.62

24" Grendel with same 123gr Target Load at 2600fps

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Range Velocity Energy Trajectory TOF Drift (yards) (fps) (ft-lb) (MILS) (sec) (MILS) 0 2600 1846 0.00 0.0000 0.00 50 2504 1712 -0.36 0.0588 -0.11 100 2409 1585 -0.00 0.1199 -0.22 150 2317 1466 -0.16 0.1833 -0.34 200 2227 1354 -0.46 0.2494 -0.46 250 2139 1249 -0.83 0.3181 -0.58 300 2052 1150 -1.26 0.3897 -0.71 350 1968 1058 -1.73 0.4643 -0.85 400 1885 971 -2.24 0.5422 -0.99 450 1805 889 -2.78 0.6235 -1.13 500 1725 813 -3.37 0.7085 -1.29 550 1648 742 -3.99 0.7975 -1.45 [B]600 1572 675 -4.66 0.8907 -1.62[/B] 650 1497 612 -5.38 0.9884 -1.80 700 1424 554 -6.15 1.0911 -1.98 750 1353 500 -6.98 1.1992 -2.18 800 1284 451 -7.86 1.3130 -2.38 850 1218 405 -8.82 1.4329 -2.60 900 1154 364 -9.85 1.5595 -2.83 950 1097 329 -10.96 1.6930 -3.07 1000 1060 307 -12.16 1.8323 -3.32

At 600yds, you see the practical difference between the two is 1.6 Mils of wind deflection for the 2600fps load, and 1.8 Mils for the 2450fps load...a whopping .2 Mils. Trajectory is 4.7 Mils for the 2600fps load, and 5.4 Mils for the 2450fps load, or a .7 Mil difference, which is noteworthy, but just a different hold for the shooter. Again, with the right powder/system, we can run the 16" gun at 2600fps with a 123gr if we really want to, but do we need to?

You can also safely run a current 16" Grendel with 100gr projectiles at 2700fps. Bill A. himself has told me that analyzing only muzzle velocities across a large population of 20" and 24" guns, you will not be able to identify which ones were 24" and which ones were 20", as they overlap each other, so a 24" is totally unnecessary for military applications.

Again, you really don't need a longer, bulkier, heavier case to drive any weight of projectile from 85gr-130gr from the current Grendel case. It will take insane levels of pressure in the right gun with a larger bolt, but do we really need that kind of pressure? No we do not.

I can also assure you that a 16" Grendel is an entirely different animal than even a 20" 5.56 NATO. Energy on-target and wind deflection are different ball games with the Grendel. You're looking at diminishing returns by increasing the case length, with increasing penalties. Bulk, recoil, barrel life, and weight are the penalties, leaning towards a 6.5x47 Lapua, which is super over-kill for a GPC.

If you want to increase the pressure to 54,000 psi, using a larger bolt would solve that requirement, and no larger case would be needed. With an industrial powder, you could easily run a 130gr projectile at 2550-2600fps, maybe faster. One of the forum members has achieved 2700fps with the 130gr Norma Golden Target using CFE223 powder out of his 24" Grendel, loaded to 2.300" COL, fed from the mag.

If you run the numbers, you'll see just how little these differences in barrel length and downrange performance equate to each other. The UK would be better off with a Gen II LMT MRP system on the AR15 frame (not the AR10/7.62 NATO), chambered in 6.5 Grendel for DM's, along with a new Multi-Role LMG chambered in 6.5 Grendel. Both systems would use a purpose-designed bolt with larger lugs, without worry of compatibility with the US AR15 civilian market.

I have spoken extensively with Lapua's R&D personnel, and they have run the Grendel from a bolt gun at frightening pressures, delivering 3400fps with 123gr Lapua Scenars, to see just how much the case can take. They exceeded .300 Winchester Magnum pressure limitations by 15%, and the brass was trashed, but didn't fail.

Nobody wants or needs anything close to those pressures from the Grendel. A 16" gun is just fine, with a purpose-build industrial powder and military load, within the AR15 receiver set size and existing magazine profile. The 7.62x51 LMT L129A1 system is a beast to carry, and a Grendel replacement would be very welcome to the lads, plus they would get a magazine capacity increase as well.

If you keep the loading at current Grendel pressures, you end up with a weapon life cycle much longer than one that runs higher pressures, and a powder could be developed specifically for it to get the velocity you need, without peaking the pressure much above 50,000psi.