300 BLK vs 5.56mm for barrel length efficiency

These graphs illustrate the diminishing returns of velocity gain as a function of barrel length. We know that for 5.56mm, a 24 inch barrel is a really efficient one. The slope of the velocity curve at 24 inches is equal to the slope of the velocity curve for 6.8 at 19 inches and 300 BLK at 16 inches. 20 inches in 5.56mm matches about 13.5 inches in 300 BLK. 16 inches in 5.56mm is like a 13 inch 6.8 and 10.5 inch 300 BLK in this regard. A 14.5 inch 5.56mm barrel matches a 10 inch 300 BLK barrel as far as slope of velocity gain. An 11 inch 5.56mm barrel is about like a 300 BLK at 7.5 inches. 20 inches in 300 BLK? Might as well be a 29.5 inch 5.56mm barrel in terms of how much left there is to get out of it by going longer - so I would consider that that longest anyone should want to do and almost everyone should stay with 16 inches.

http://img692.imageshack.us/img692/3...20210at814.png

Any chance of modifying that chart to also have a graph with the energy, and/or impulse?

I am adding energy to it now. It may make more sense to look at the slope based on diminishing returns of energy rather than velocity.

Scrap all this. I am redoing it with a different method.

Very interested in this. I'm bouncing between an 8", 9" and 10.5" build. So many functional variables...

I am still looking for a trajectory chart for the 300 blk, 7.62x39, 6.8, 5.56, and 7.62.
I know, lots of variables bullet size and weight etc. I am really only wondering about high velocity rounds. Anyone have one handy?

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Originally Posted by krm375

I am still looking for a trajectory chart for the 300 blk, ...

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+1 to this.

+2 I'd like as much info as you'd be willing to provide Mr. Silvers.

Wow, Robert:D was just discussing this tonight as I will be getting a 300BLK upper soon and our 4th AAC suppressor for it and my brother and I were trying to work out which barrel length was going to suit our needs. I really look forward to you putting this together for us to help all at M4C make better decisions on your new cartridge! Thanks:D

What would be the optimum zero for the flattest trajectory and longest engagement range, without hold over, for the 300BLK, similar to the 50/200M zero for the 5.56?