Every rifle cartridge headspaces one of a few ways, and the way its case is built at the base dates the design almost as well as a headstamp. This set has belted magnums, beltless magnums, AR rounds that follow the .223's rules, and two lever-gun rounds that disagree with each other.
Reading the base takes a second.
Belted: the 1912–1960s convention
.375 h&h magnum ammo carries the original belt — Holland & Holland put it there in 1912 so the .375's shallow shoulder had something to headspace on — and 300 weatherby bullet inherited it in 1944 when Roy Weatherby built his most popular magnum on a belted H&H-derived case. The belt does nothing for accuracy; it dates the design.
Beltless and fat: the 1999–2018 convention
300 rem ultra dropped the belt in 1999 on a .404 Jeffery-derived case, and every later long-range .30 followed — 300prc ammo in 2018 among them. 375 cheytac ammo is beltless too, a .408 CheyTac case necked down, with the fat body and sharp shoulder that mark the extreme-long-range generation.
Beltless and standard-diameter
.375 ruger ammo is the compromise: a beltless case whose base matches the diameter of the old H&H belt, so it fits a standard magnum bolt face in a standard-length action — the reason Hornady and Ruger chose it as the parent for their compact magnums.
Small cases on the .223 pattern
300 hamr ammo and 375 socom are AR-15 rounds and headspace on the shoulder like the .223 they share a rifle with — one on a lengthened .223 case, the other on a rebated-rim .458 SOCOM case necked down. Neither is a magnum in any sense; they belong here as relatives of the rounds beside them.
The two lever-gun cases
.308 me is rimmed, because it lives in a tube-magazine Marlin and was built from the rimmed .307 Winchester case. 300 savage ammo for sale is rimless, because the Savage 99's rotary magazine never needed a rim. Both are lever-gun rounds; the case tells you which rifle.
The one confusion that matters
A belted magnum and a beltless one of the same bore do not interchange, and neither fits a rifle built for the other. Read the base, then the rifle's stamp.
Never substitute a similarly-named cartridge without confirming case dimensions and headspacing against your rifle's chamber markings or manual, and verify current stock and any state shipping restrictions before ordering.
