01-13-2012, 12:31 PM
The .280 pushing a 7mm 168 VLD type bullet versus the 7.62 pushing a M118 173gr Special Ball leans in favor of the 7mm, and makes it a true 800m cartridge. That is with the 7mm 168 VLD starting 100fps slower at 2400fps and the M118 at 2500fps, which is book value for the M24 Sniper Rifle.
With the .280/30, we are looking at faster velocities that make the 7.62 NATO not worth looking at, and you have bullets of similar weights, similar velocities, with the sectional density and aerodynamic advantage clearly in the 7mm's favor. I just ran the numbers side-by-side with the G7 BC values for a 168 7mm VLD at .313, and the M118's .240 G7 BC. The 7mm retains 911 joules at 800m, while the 7.62 M118 only retains 692 joules at that range, having started 100fps faster at the muzzle.
Trajectory for the 7mm at 800m is 9.4 Mils, while the M118 is 10 Mils. Wind drift is 2 Mils for the 7mm at 800m, while M118 is 2.8 Mils at that distance. Another thing to look at is that the 7mm can still do better than the .30 bores with the 139gr bullets, at the same or even faster velocities, since a 139gr 7mm tends to have a higher BC advantage over the 168gr class .30 cal match bullets even.
For a DMR and LMG, the 7mm makes a lot more sense to me for trajectory and retained energy for that era, and the 7mm would still be filling the roles that 7.62 NATO has performed over the past 57 years, with machinegunners on the ground and in the air seeing less drop and drift at extended ranges, with lighter overall weight.
With the .280/30, we are looking at faster velocities that make the 7.62 NATO not worth looking at, and you have bullets of similar weights, similar velocities, with the sectional density and aerodynamic advantage clearly in the 7mm's favor. I just ran the numbers side-by-side with the G7 BC values for a 168 7mm VLD at .313, and the M118's .240 G7 BC. The 7mm retains 911 joules at 800m, while the 7.62 M118 only retains 692 joules at that range, having started 100fps faster at the muzzle.
Trajectory for the 7mm at 800m is 9.4 Mils, while the M118 is 10 Mils. Wind drift is 2 Mils for the 7mm at 800m, while M118 is 2.8 Mils at that distance. Another thing to look at is that the 7mm can still do better than the .30 bores with the 139gr bullets, at the same or even faster velocities, since a 139gr 7mm tends to have a higher BC advantage over the 168gr class .30 cal match bullets even.
For a DMR and LMG, the 7mm makes a lot more sense to me for trajectory and retained energy for that era, and the 7mm would still be filling the roles that 7.62 NATO has performed over the past 57 years, with machinegunners on the ground and in the air seeing less drop and drift at extended ranges, with lighter overall weight.