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Originally Posted by Formynder
So I know enough to know the best grain bullets for the various twist rates on my rifles, but I saw this today by Theohazard:
The 300 Blackout is basically a 30 caliber bullet in a 5.56 case. With 115 gr. supersonic loads you get very similar ballistics to a 7.62x39 or a .30-30, and with 220 gr. subsonics you get a super-quiet suppressed round that will still cycle the action and can still make good hits out to about 200 meters or so.
I thought that generally speaking, heavier bullets had more grains of gun powder in them and thus had more force and were generally faster. How is it that the subsonic load has nearly twice the grains of the supersonic load in this case? Is my understanding of bullets completely off?
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Grain is not a measure of the powder in a cartridge, but the weight of the bullet. In Theohazard's example, the 115 grain bullet is much lighter, therfore faster, than the heavier 220 grain subsonic, therefore slower (all other factors being equal) bullet.
http://en.wikipedia.org/wiki/Grain_(unit)