JASmith Wrote:LR1955 and others have argued that probability of hit out to 400-600 meters is of critical importance and that any new system needs to shine in at least one area.
Given the fundamental need to get a hit, it seems odd that we've spent a lot of time discussing on-target effects, ammunition weight, and recoil but almost none on trajectory and wind-drift. These areas are ones where higher-velocity and moderately well-shaped bullets might result in a significant improvement.
Tony Williams Wrote:If we were sticking to lead+steel cored bullets I would choose 6.5mm as the ideal calibre, but with copper+steel (or even just steel) bullets as seems mandatory nowadays, getting sufficient weight within a reasonable length becomes a problem for long, VLD bullets. So I am agnostic over the exact calibre, it all depends on how the sums work out; the answer could be 6.8mm or even 7mm.Curiosity got the better of me, so I ran some tables for comparison. Had to make some assumptions, estimations and extrapolations regarding muzzle velocities from 20-inch barrels, but I think the figures are fairly close. On the .277" and .264" bullets, I used the BCs for Barnes' solids as the best available surrogates for eco-friendly, military ball projectiles.
We may be able to get away with being close enough to M80 performance for the difference not to be significant, rather than exactly matching it. However, if the long-range performance falls noticeably short then the new round won't be able to replace 7.62mm and the argument for it will thereby be substantially weakened IMO.
Range - yards _0_ _100 _200 _300 _400 _500 _600 _700 _800 _900 1000
.308" 147gr @ 2700fps BC=0.418
Velocity - fps 2700 2488 2285 2094 1912 1740 1579 1435 1306 1198 1111
Energy - ft-lb 2379 2019 1705 1430 1193 _988 _814 _672 _556 _468 _403
Path - inches 0.0 44.6 83.7 116.0 140.4 155.2 158.5 147.8 120.3 72.2 0.0
Drift - inches 0.0 _0.4 _1.6 __3.7 __6.9 _11.3 _17.0 _24.2 _33.1 43.6 55.9
.277" 120gr @ 2600fps BC=0.438
Velocity - fps 2600 2402 2213 2033 1862 1700 1550 1415 1294 1192 1110
Energy - ft-lb 1801 1537 1304 1101 _924 _770 _640 _533 _446 _379 _328
Path - inches 0.0 46.7 87.4 121.0 146.1 161.1 164.2 152.7 123.8 74.1 0.0
Drift - inches 0.0 _0.4 _1.6 __3.7 __6.9 _11.2 _16.9 _24.1 _32.8 43.1 55.0
.264" 110gr @ 2600fps BC=0.452
Velocity - fps 2600 2408 2224 2049 1883 1725 1577 1443 1322 1219 1134
Energy - ft-lb 1651 1416 1208 1025 _866 _726 _607 _509 _427 _363 _314
Path - inches 0.0 45.5 85.1 117.6 141.8 156.2 158.8 147.5 119.4 71.4 0.0
Drift - inches 0.0 _0.4 _1.5 __3.6 __6.7 _10.8 _16.3 _23.1 _31.4 41.4 52.8
Verry intrresting, no?
Arggh! The new forum format is too narrow for 1000-yard data. I guess future tables will have to be limited to 800 yards...