[Borg Warner]

The 300 BK Has far greater sexual density.

 

[Borg Warner]

I'd like to see a 300 subsonic test against 7.62x39 subsonic. I was dead set on a 300 pistol but I am considering going 7.62x39 but I haven't seen any good sub sonic tests of the 7.62. the price of ammo being the main driver for me. Both can be reloaded for close to the same price but I would need to buy/make 300 cases. I have a ton of 7.62 brass I've saved over the years.

300 blackout ballistics can be duplicated with the 7.62x39 and factory loaded subsonic ammo is available including a 182 grain load from PPU and a 196 grainload from Brown bear. Standard 762x39 barrel twists will stabilize heavy bullets and 762x39 supersonic ballistics are superior to 300 BK.

 

[Borg Warner]

How so, exactly. And in what barrel lengths, specifically.

Sustantially more case capacity. 7.62x39 has a case capacity of 35.6 gr H2O .But with an overall case length of 35mm, the 300 BLK has a case capacity of approximately 19.2 grains but can be as much as 23 grains with thinner brass cases. The reduced case length was required to allow it to fit into a standard M4 carbine magazine while being loaded with a longer 30 caliber bullet which takes up up case capacity.

Maximum pressure levels for the 300 BK are higher but only at SAAMI pressure levels. Those pressure levels can be safely exceeded since European and Russian CIP Max pressire levels are higher, 51,000 psi maximum Piezzo pressure CIP vs 45,000 maximum Piezzo pressure SAAMI.

And as far as barrel length, More barrel length, More velocity. There is no magic barrel length that will give you significantly more velocity out of a shorter barrel with the same load.