Grendel as a Universal Infantry Cartridge

[SHORT-N-SASSY]

. . . To get more velocity it takes more pressure, henceforth less velocity equals less pressure. . . .

To recap:

6.5mm Grendel SAAMI Maximum Average Pressure (MAP): 52,000 psi (http://kwk.us/pressures.html);

6.5mm Grendel, 20-inch barrel:
100 gr Alexander Arms Berger Open-Tip Match: 2,847 fps;
123 gr Alexander Arms Lapua Scenar: 2,627 fps;
123 gr Hornady A-MAX: 2,582 fps.
(http://www.rifleshootermag.com/2011/11/0...evolution/);

"It is a double base ball type and will be loaded to 3550 bar [51,488 psi] in line with existing weapon and ammunition setup." (www.ar15.com/forums/t_2_453/209394_Steel_Case_.html&page=1#i1882699);

6.5mm Grendel, 20-inch barrel:
100 gr WOLF FMJ -BT, 2,600 fps.
(http://www.ar15.com/forums/t_3_121/64961...IN_OP.html).

The big question: In view of the above, how do Alexander Arms and Hornady, loading their respective 6.5mm Grendel ammo, operating at approximately the same chamber pressure as WOLF, and using projectiles that weigh 23% greater than the 100-grain projectile used in the WOLF 6.5mm Grendel Steel Case ammo, manage to achieve approximately the same muzzle velocity --- from the same 20-inch barrel length?