THE HANDLOADING BENCH
308 Winchester Rides Again Part 3 By Laurie Holland
consult, but what is not in dispute is that the closer the bullet gets to the speed of sound (1,122 fps / 1.0 M), the greater the likelihood and severity of turbulence in the airflow around the bullet’s body and tail. When I first ran these figures, the discrepancy was so great I had trouble believing the results, but Bryan Litz, Berger’s ballistician assures me there is no mistake.
New ‘heavies’ only just arrived in the UK. Left to right: 155gn Sierra MK (for compari- son); 200gn Berger Hybrid; 208gn Hornady HPBT; 215gn Berger Hybrid; 230gn Berger Hybrid.
of energy if both combinations produce the same chamber pressure. 3,108 ft/lbs = 2,582 fps MV with a 210gn bullet, very much in line with those actually produced by heavy bullet F/TR users. The 155.5’s G7 BC is 0.237, that of the two-ten 0.320, the difference arising entirely from their weights, or more precisely their sectional density values which is a fixed weight to calibre ratio. That’s a substantial gain at 1,000yd both in retained velocity and reduced wind drift. High retained velocity is important to keep our bullet out of the transonic speed zone, or at any rate to reduce its exposure to transonic flight. This speed zone starts at 1.2 to 1.3 MACH depending on which authority you
Table 1 (Overleaf) takes the Berger 155.5 at 3,000 fps as a benchmark and shows how the 190gn to 230gn models compare using equivalent MVs. We see that judicious heavy bullet selection can give us nearly 150 additional fps at the 1,000-yard target taking the bullet out of transonic flight and potentially reduce
wind drift by up to two and a half MOA even compared to that most efficient of the 155s. The gains will be larger still against the NRA’s RWS manufactured ammunition with its early model and much lower BC 155gn Sierra Palma MatchKing. That 10 mph 90-degree crosswind is an artificial construct of course, what matters is any change in wind speed and/or direction between shots. To get a feel what a ‘heavy’ might give us, I played around with wind values in the program to get one that moves the 155.5 at 3,000 fps by 1.2-MOA at this distance. Assuming our bullet would have hit the V Bull dead centre if the wind hadn’t changed from the previous shot, it now scores a line-cutter ‘Three’. Retain the wind speed value, but rerun the program with those 200/210s with BC values
Run the MVs and BCs through Berger Bullets’ G7 ballistic program and we get; Bullet
i7
155.5 BT FB 0.988 210 BT LR
0.988 BC
0.237 0.320
V0 (fps) 3,000 2,582
V1,000 (fps) 1,304 (1.16 M) 1,371 (1.22 M)
D1,000 (MOA / Inches) 8.7 / 91.1” 7.3 / 76.1”
Standard ballistic conditions (59°F, 29.92-inches Hg atmospheric pressure) apply. D1,000 = wind drift at 1,000yd in a 10 mph 90-deg crosswind. M= MACH.
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