History
Winchester introduced the .300 Winchester Magnum in 1963, the last of the four belted magnums it built on a shortened .375 H&H case. The goal was magnum .30-caliber performance, high velocity and a flat trajectory, in a cartridge that still fed from a standard-length action rather than the long magnum actions the full .375 H&H demanded.1
The design moved the shoulder forward for more powder capacity, which left the .300 Win Mag with a notably long body and a short neck. It became one of the most successful magnums ever, and from the 1980s on it served as a military and police sniper round, chambered in systems like the M24 and loaded as the A191 cartridge.1
Lineage
The .300 Winchester Magnum belongs to the belted family derived from the .375 H&H Magnum, shortened, blown out, and necked to .30 caliber.1 Its siblings on that case are the .264, .338, and .458 Winchester Magnums. It fires a .308 inch (7.82mm) bullet, and like all of the H&H-derived magnums it headspaces on the belt, the raised band just ahead of the extractor groove.
Specifications
| Spec | Value |
|---|---|
| Case type | Belted, bottlenecked |
| Bullet diameter | 7.82 mm (.308 in) |
| Neck diameter | 8.61 mm (.339 in) |
| Shoulder diameter | 12.42 mm (.489 in) |
| Belt diameter | 13.51 mm (.532 in) |
| Rim diameter | 13.03 mm (.513 in) |
| Case length | 66.55 mm (2.620 in) |
| Overall length | 84.84 mm (3.340 in) |
| Case capacity | ~91.5 gr H2O (nominal; varies by brand) |
| Primer size | Large rifle (magnum) |
| Belted | Yes (headspaces on the belt) |
| Rifling twist | 1 in 10 in (254 mm, SAAMI and C.I.P. standard)2 |
| Max pressure | 64,000 psi (SAAMI); 4,300 bar / 430 MPa (C.I.P.)2 |
| Recommended barrel | 30 in, 1:10 twist |
Barrel Design
The .300 Winchester Magnum burns a large charge of slow powder, so it wants every inch of barrel to let that powder finish working. Thirty inches is where this cartridge reaches its potential, and the tables below are computed there. You gain real velocity over a 26 inch tube, which matters when you are driving heavy, high-BC bullets out past 1,000 yards. A hunter who carries the rifle into the field is well served by a shorter 24 to 26 inch barrel, trading some velocity for a lighter, handier package.
Twist is the other decision. The 1:10 standard stabilizes the 178 to 215 grain bullets most long-range shooters run, but if you load the heaviest 215 to 230 grain match bullets, a 1:9 gives more margin at transonic range. For the long-range mission here the baseline is 30 inches at 1:10.
Range Ammo Performance
Prvi Partizan · 145 gr FMJ Boat Tail $1.38/rd
| Range (yd) | Velocity (fps) | Elevation (mil) | Energy (ft-lb) | Windage (mil) |
|---|---|---|---|---|
| 0 | 3400 | -0.2 | 3722 | 0.4 |
| 100 | 3158 | 0.0 | 3210 | 0.2 |
| 200 | 2928 | -0.2 | 2760 | 0.4 |
| 300 | 2710 | -0.7 | 2364 | 0.6 |
| 400 | 2502 | -1.2 | 2015 | 0.8 |
| 500 | 2303 | -1.9 | 1708 | 1.0 |
| 600 | 2114 | -2.6 | 1438 | 1.3 |
| 700 | 1933 | -3.5 | 1203 | 1.6 |
| 800 | 1763 | -4.5 | 1001 | 1.9 |
| 900 | 1605 | -5.6 | 829 | 2.2 |
| 1000 | 1461 | -6.8 | 687 | 2.6 |
| 1100 | 1332 | -8.3 | 571 | 3.0 |
| 1200 | 1223 | -10.0 | 481 | 3.4 |
| 1300 | 1135 | -11.9 | 415 | 3.9 |
| 1400 | 1067 | -14.1 | 367 | 4.4 |
| 1500 | 1014 | -16.6 | 331 | 4.8 |
| 1600 | 971 | -19.3 | 303 | 5.3 |
| 1700 | 933 | -22.4 | 280 | 5.8 |
| 1800 | 900 | -25.7 | 261 | 6.3 |
| 1900 | 870 | -29.4 | 244 | 6.7 |
| 2000 | 843 | -33.3 | 229 | 7.2 |
| 2100 | 817 | -37.5 | 215 | 7.6 |
| 2200 | 793 | -42.0 | 203 | 8.1 |
| 2300 | 771 | -46.8 | 191 | 8.6 |
| 2400 | 750 | -52.0 | 181 | 9.0 |
Muzzle velocity 3400 fps is estimated at 30 in from the 26 in factory figure of 3280 fps at about 30 fps per inch. Expect your own barrel to read a little differently. Velocity is color coded green supersonic, yellow transonic, red subsonic; treat transonic and subsonic rows as approximate.
Match Ammo Performance
Hornady Match · 195 gr ELD Match $2.30/rd
| Range (yd) | Velocity (fps) | Elevation (mil) | Energy (ft-lb) | Windage (mil) |
|---|---|---|---|---|
| 0 | 3110 | -0.3 | 4188 | 0.3 |
| 100 | 2954 | 0.0 | 3778 | 0.1 |
| 200 | 2802 | -0.3 | 3399 | 0.3 |
| 300 | 2654 | -0.8 | 3049 | 0.5 |
| 400 | 2510 | -1.4 | 2727 | 0.6 |
| 500 | 2370 | -2.1 | 2433 | 0.8 |
| 600 | 2236 | -2.8 | 2164 | 1.0 |
| 700 | 2106 | -3.7 | 1919 | 1.2 |
| 800 | 1980 | -4.5 | 1697 | 1.4 |
| 900 | 1858 | -5.5 | 1494 | 1.6 |
| 1000 | 1739 | -6.6 | 1310 | 1.9 |
| 1100 | 1624 | -7.7 | 1142 | 2.1 |
| 1200 | 1513 | -9.0 | 991 | 2.4 |
| 1300 | 1405 | -10.4 | 854 | 2.7 |
| 1400 | 1301 | -12.0 | 732 | 3.1 |
| 1500 | 1202 | -13.7 | 625 | 3.4 |
| 1600 | 1114 | -15.7 | 538 | 3.8 |
| 1700 | 1066 | -17.9 | 492 | 4.2 |
| 1800 | 1033 | -20.3 | 462 | 4.7 |
| 1900 | 1004 | -23.0 | 437 | 5.1 |
| 2000 | 978 | -25.9 | 414 | 5.4 |
| 2100 | 954 | -29.0 | 394 | 5.8 |
| 2200 | 931 | -32.3 | 375 | 6.2 |
| 2300 | 909 | -35.8 | 358 | 6.6 |
| 2400 | 889 | -39.5 | 342 | 7.0 |
Muzzle velocity 3110 fps is estimated at 30 in from the 24 in factory figure of 2930 fps at about 30 fps per inch. Expect your own barrel to read a little differently. Velocity is color coded green supersonic, yellow transonic, red subsonic; treat transonic and subsonic rows as approximate.
Trajectory
FAQ
What does the .300 Win Mag headspace on?
The belt, the raised band just ahead of the extractor groove.2 That is the defining feature of the .375 H&H-derived magnums, and it is why the cartridge works in a standard-length action.
What twist rate do I need for heavy bullets?
One turn in 10 inches is the standard and handles the common 178 to 215 grain bullets. For the heaviest 215 to 230 grain match bullets, many long-range shooters step to a 1:9 for extra stability margin at distance.
What is a good practice load versus a match load?
For practice and hunting, the Hornady 178 grain ELD-X at 2,960 feet per second from a 26 inch barrel. For match work, the Federal Gold Medal Berger 215 grain Hybrid at 2,850 feet per second, with a G7 BC of 0.354.3
How does the .300 Win Mag compare to the .308 Winchester?
It holds far more powder and pushes the same .308 bullets several hundred feet per second faster, which flattens the trajectory and extends supersonic range well past the .308. The tradeoff is heavier recoil, a longer action, and more powder per shot.
Citations
- (2020). The History of .300 Winchester Magnum Sniping. Sniper Central. accessed 2026-05-30.
- (2002). C.I.P. TDCC Datasheet — .300 Winchester Magnum. Commission Internationale Permanente (C.I.P.). accessed 2026-05-30.
- (2024). Berger 30 Caliber 215 gr Hybrid Target. Berger Bullets. accessed 2026-05-30.