Barrel Lengths And Case Capacities

Rifles with short barrels are becoming very commonplace. Standard for many AR-15s in .223 is a barrel length of 16″. That’s the shortest you can legally own without a Short Barreled Rifle (SBR) Federal $200 tax stamp. The special purpose SSK Hoaginator M16 sports a 6″ barrel, and 55-grain ball does about 2,150 fps. AR rifles in .308 are often 16″ for civilian rifles, and shorter for military and LE, and are generating a great deal of interest. Riflemen have suddenly realized a 16″ barrel gives away literally nothing to a 24″ barrel in accuracy or power.

The .30-06 was the US round of choice in WWI, WWII and Korea and found usage in Springfield bolt guns, Garands, BARs and Browning machine guns, and is still in military use in many countries.

Somebody realized the .30-06 case could be reduced in size without reducing ballistics due to improvements in powders. That turned out to be the 7.62X51 or .308 Winchester in civilian jargon, initially championed in the M14. No doubt about it the military version easily beats the .30-06 by a considerable margin ballistically. Normally the military 150-grain 06 gives 2,700 fps from a 24″ barrel. I’ve chronographed some .308 military 150-grain ammo (usually about 144 grains) at an average of 2,975 fps from a 24″ barrel.

You might think the larger .30-06 case loaded with modern powders, to the same pressures as the .308, might well surpass it ballistically — and you would be correct. Note though, firing just one high pressure round through an M-1 Garand will probably bend the operating rod and drastically reduce accuracy. Continued use of over-pressure .30-06 ammunition can break the rear of the receiver. I’ve seen about 20 of those.
By J.D. Jones

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