History
Take Hornady's .300 PRC, a beltless 2018 magnum built on a modern non-rebated case with a long throat for heavy high-BC bullets, and neck it to 7mm (.284 inch). The 7mm bullet gives up a little frontal area but brings better sectional density and ballistic coefficient, and the result is one of the flattest 7mm magnums going. It is a wildcat built for extreme long range and long-range hunting.
There is no SAAMI or C.I.P. specification behind it, so the dimensions here are derived from the parent and should be treated as approximate. It runs with the 28 Nosler and 7mm RUM at the top of the class. The long cartridge overall length is the whole point: the 190 to 195 grain match bullets seat out of the case, keeping powder capacity while running the heaviest 7mm projectiles.
Lineage
Necked to .284 inch (7.21mm), it keeps the parent's beltless .532 inch case head, roughly 30 degree shoulder, and 3.7 inch overall length. It feeds from a long or magnum action on a large rifle magnum primer. The parent is the .300 PRC; the peers are the other top-tier 7mm magnums, the 28 Nosler, 7mm RUM, and 7mm Weatherby, plus the smaller standardized 7mm PRC.
Specifications
| Spec | Value |
|---|---|
| Case type | Rimless, beltless, bottlenecked (~30° shoulder) |
| Bullet diameter | 7.21 mm (.284 in) |
| Neck diameter | 8.04 mm (.317 in) |
| Shoulder diameter | 13.08 mm (.515 in) |
| Rim diameter | 13.51 mm (.532 in) |
| Case length | 65.53 mm (2.580 in) |
| Overall length | 93.98 mm (3.700 in) |
| Case capacity | ~89 gr H2O (nominal) |
| Primer size | Large rifle magnum |
| Belted | No |
| Rifling twist | 1 in 8 in (recommended, for heavy 7mm match) |
| Max pressure | No SAAMI/C.I.P. standard; load to .300 PRC pressure |
| Recommended barrel | 28 in, 1:8 twist |
Dimensions are derived from the parent .300 PRC; this is a wildcat with no published standard, so treat the figures and the cutaway as approximate.
Barrel Design
The 1:8 twist is the call that matters. Those long 180 to 195 grain high-BC bullets need the fast twist to stabilize through the transonic range at distance, and a slower twist suited to 140 to 160 grain bullets would waste the case. Lighter, smaller 7mm cartridges already cover that job for less powder.
A large overbore magnum also needs barrel length: the slow powders finish burning and muzzle velocity settles shot to shot. The baseline I'd recommend sits at 28 inches, which collects most of the velocity in a barrel that still balances on a long-range rifle, with a 30 inch tube adding a little more for those who can manage it. The tradeoff is barrel life, since an overbore magnum erodes its throat faster than a 7mm PRC and needs a rebarrel sooner. The tables below come from representative handloads at that 28 inch barrel; with no factory 7mm-300 PRC ammunition to lean on, confirm your own on a chronograph before trusting any dial.
Handload Performance
Handload · 195 gr Berger EOL Elite Hunter
| Range (yd) | Velocity (fps) | Elevation (mil) | Energy (ft-lb) | Windage (mil) |
|---|---|---|---|---|
| 0 | 3020 | -0.3 | 3949 | 0.3 |
| 100 | 2902 | 0.0 | 3647 | 0.1 |
| 200 | 2787 | -0.3 | 3363 | 0.3 |
| 300 | 2674 | -0.8 | 3096 | 0.4 |
| 400 | 2564 | -1.4 | 2846 | 0.5 |
| 500 | 2456 | -2.1 | 2611 | 0.7 |
| 600 | 2351 | -2.8 | 2392 | 0.8 |
| 700 | 2248 | -3.6 | 2188 | 1.0 |
| 800 | 2148 | -4.4 | 1998 | 1.1 |
| 900 | 2051 | -5.3 | 1821 | 1.3 |
| 1000 | 1956 | -6.2 | 1657 | 1.5 |
| 1100 | 1864 | -7.2 | 1504 | 1.7 |
| 1200 | 1773 | -8.3 | 1361 | 1.9 |
| 1300 | 1684 | -9.4 | 1228 | 2.1 |
| 1400 | 1598 | -10.6 | 1105 | 2.3 |
| 1500 | 1513 | -12.0 | 991 | 2.6 |
| 1600 | 1430 | -13.4 | 885 | 2.8 |
| 1700 | 1350 | -14.9 | 789 | 3.1 |
| 1800 | 1272 | -16.6 | 700 | 3.4 |
| 1900 | 1197 | -18.4 | 621 | 3.7 |
| 2000 | 1129 | -20.4 | 551 | 4.0 |
| 2100 | 1083 | -22.6 | 508 | 4.4 |
| 2200 | 1054 | -24.9 | 481 | 4.7 |
| 2300 | 1030 | -27.4 | 460 | 5.1 |
| 2400 | 1009 | -30.1 | 441 | 5.4 |
| 2500 | 989 | -33.0 | 424 | 5.8 |
| 2600 | 970 | -36.0 | 408 | 6.1 |
Muzzle velocity 3020 fps is the factory figure from a 28 in test barrel. 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 barrel length and twist should I run?
A 1:8 twist for the heavy 180 to 195 grain 7mm match bullets the cartridge is built around, and a 28 inch barrel to collect its velocity. A 30 inch barrel adds a little more speed if the rifle can carry it, but 28 inches is the practical balance of velocity and handling.
Is the 7mm-300 PRC a SAAMI cartridge?
No. The 7mm-300 PRC is a wildcat with no SAAMI or C.I.P. standard. You neck down factory .300 PRC brass to 7mm and handload it; there is no factory 7mm-300 PRC ammunition. The dimensions on this page are derived from the parent .300 PRC and are approximate.
How does it compare to the 28 Nosler and 7mm PRC?
The 7mm-300 PRC and 28 Nosler are near-peers at the top of the 7mm magnum class, trading raw capacity for the PRC case's long throat that seats heavy bullets out better. The 7mm PRC is the smaller, standardized, factory-supported option, easier on barrels and far easier to feed. Most shooters should start with the 7mm PRC unless they specifically need the extra reach the wildcat delivers.
What is it good for?
Extreme long range and long-range hunting, where a flat trajectory and high retained energy past 1,000 yards justify the recoil, powder burn, and barrel wear. It is not a sensible choice for an all-around or high-volume rifle; that is the smaller 7mm cartridges' job.