: Win m70 (post-64)
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technical cartridge drawing
A commercial cartridge, probably the most successful of the short-fat genera of cartridges introduced beginning with Remington's 300 RUM. The 300 WSM provides (nearly) 300 Win Mag ballistics from a 308 length cartridge allowing for chambering in short (2.86") action firearms. The whole WSM line of cartridges has developed quite a following (including the present author).
Although the initial (wildcat) short fat cartridges [like Rick Jamison's 300 Jamison] were based on the 404 Jeffery case trimmed and necked down, Winchester states that that their series of WSM cartridges are original designs and not based on another cartridges modified (and looking closely at the dimension this appears to be the case).
The case capacity of the 300 WSM is 80.4 gr (of water) full case, 72.9gr with a flat base bullet seated .400". In comparison the 300 Win Mag is 87.0gr and 82.1gr, respectively. Jamison's 300, with a .1" longer body measures: 82.0 and 74.4grs. Ballistically, given the improved volume to surface area, the 300 WSM essentially equals the Win Mag's performance even with its slightly smaller capacity. The 300 WSM is usable for any task the 300 Win Mag is capable of. Other cartridges of this class are: the 300 H&H Mag, 81.3 and 74.3gr; the 300 Wby, 91.0 and 83.5gr; 30 Newton 83.3 and 75.8gr. These are well short of the 30-378 (120gr, 112gr) or 300 RUM (110gr, 102gr) class cartridges.
Nominal bullet diameter is .308"; SAAMI lists the maximum pressure at 65kpsi.