Here's some data from realguns.com on the 338/378
Warning: Bullet selections are specific, and loads are not valid with substitutions of different bullets of the same weight. Variations in bullet length will alter net case capacity, pressure and velocity. Primer selection is specific and primer types are not interchangeable. These are maximum loads in my firearms and may easily be excessive in others. All loads should be reduced by 10%, and developed following safe handloading practices as represented in established reloading manuals produced by component manufacturers. Presentation of these loads does not constitute a solicitation for their use, nor a recommendation.
Cartridge: .338-378 Weatherby Magnum
Rifle: Weatherby Mark V Accumark Max COL: 3.763"
Barrel: 26" Reloading Dies: RCBS, CH4D
Max case length: 2.913" Group distance: 100 yards
Note: Weatherby Mark V Action rifles only
Bullet Type Bullet
Weight Bullet
Diameter C.O.L. Net Water
Capacity Powder
Type Charge Primer
Type Muzzle
Velocity Muzzle
Energy Group
Size
Nosler Ballistic Tip 200 .338" 3.760" 126.4 Reloder 22 112.0 CCI 250 3380 5075 1.2
Nosler Ballistic Tip 200 .338" 3.760" 126.4 Reloder 25 118.0 CCI 250 3340 4955 0.7
Nosler Ballistic Tip 200 .338" 3.760" 126.4 H 1000 117.7 CCI 250 3320 4896 0.7
Nosler Ballistic Tip 200 .338" 3.760" 126.4 IMR 7828 111.5 CCI 250 3350 4985 0.5
Sierra GameKing BTSP 215 .338" 3.700" 126.6 Reloder 22 110.6 CCI 250 3275 5122 0.4
Sierra GameKing BTSP 215 .338" 3.700" 126.6 Reloder 25 117.0 CCI 250 3250 5044 0.5
Sierra GameKing BTSP 215 .338" 3.700" 126.6 H1000 117.3 CCI 250 3260 5075 0.8
Sierra GameKing BTSP 215 .338" 3.700" 126.6 IMR 7828 110.2 CCI 250 3270 5106 0.7
Speer Boat Tail 2406 225 .338" 3.680" 126.1 Reloder 22 108.5 CCI 250 3195 5101 0.9
Speer Boat Tail 2406 225 .338" 3.680" 126.1 Reloder 25 115.8 CCI 250 3200 5117 0.8
Speer Boat Tail 2406 225 .338" 3.680" 126.1 H 1000 114.5 CCI 250 3150 4959 1.0
Speer Boat Tail 2406 225 .338" 3.680" 126.1 IMR 7828 108.7 CCI 250 3200 5117 0.8
Barnes XLC 225 .338" 3.760" 124.9 Reloder 22 108.5 CCI 250 3220 5181 1.2
Barnes XLC 225 .338" 3.760" 124.9 Reloder 25 115.0 CCI 250 3190 5085 1.0
Barnes XLC 225 .338" 3.760" 124.9 H 1000 115.5 CCI 250 3210 5149 0.8
Barnes XLC 225 .338" 3.760" 124.9 IMR 7828 108.0 CCI 250 3200 5117 0.5
Barnes XLC 225 .338" 3.760" 124.9 RS Magnum 116.0 CCI 250 3240 5246 0.9
Sierra GameKing BTSP 250 .338" 3.760" 124.6 Reloder 22 104.5 CCI 250 3030 5098 0.7
Sierra GameKing BTSP 250 .338" 3.760" 124.6 Reloder 25 112.6 CCI 250 3060 5199 0.7
Sierra GameKing BTSP 250 .338" 3.760" 124.6 H 1000 111.2 CCI 250 3025 5081 0.7
Sierra GameKing BTSP 250 .338" 3.760" 124.6 H 870 122.0 CCI 250 3080 5267 1.5
Sierra GameKing BTSP 250 .338" 3.760" 124.6 IMR 7828 104.0 CCI 250 3020 5064 0.5
Speer Grand Slam 250 .338" 3.760" 126.0 Reloder 22 104.5 CCI 250 3010 5031 1.1
Speer Grand Slam 250 .338" 3.760" 126.0 Reloder 25 112.6 CCI 250 3040 5131 1.1
Speer Grand Slam 250 .338" 3.760" 126.0 H 1000 111.8 CCI 250 3020 5064 1.4
Speer Grand Slam 250 .338" 3.760" 126.0 H 870 124.0 CCI 250 3100 5336 1.8
Speer Grand Slam 250 .338" 3.760" 126.0 IMR 7828 105.7 CCI 250 3050 5165 0.9
Speer Grand Slam 250 .338" 3.760" 126.0 RS Magnum 117.0 CCI 250 3112 5377 1.3
Woodleigh Weldcore PP 250 .338 3.760" 127.0 Reloder 22 104.0 CCI 250 2990 4964 1.5
Woodleigh Weldcore PP 250 .338 3.760" 127.0 Reloder 25 111.5 CCI 250 3000 4997 1.1
Woodleigh Weldcore PP 250 .338 3.760" 127.0 H 1000 112.3 CCI 250 3010 5031 0.8
Woodleigh Weldcore PP 250 .338 3.760" 127.0 H 870 122.0 CCI 250 3040 5131 0.8
Woodleigh Weldcore PP 250 .338 3.760" 127.0 IMR 7828 106.5 CCI 250 3055 5182 1.0
Swift A Frame 275 .338 3.760" 123.6 Reloder 22 99.5 CCI 250 2845 4494 0.7
Swift A Frame 275 .338 3.760" 123.6 Reloder 25 108.4 CCI 250 2900 5137 1.3
Swift A Frame 275 .338 3.760" 123.6 H 1000 107.2 CCI 250 2875 5049 1.0
Swift A Frame 275 .338 3.760" 123.6 H 870 117.5 CCI 250 2925 5226 1.4
Swift A Frame 275 .338 3.760" 123.6 IMR 7828 101.0 CCI 250 2900 5137 0.9
