300 BLK vs 5.56mm for barrel length efficiency

[rsilvers]

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.

[TehLlama]

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

[rsilvers]

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.

[rsilvers]

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

[5cary]

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

[krm375]

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?

[M4Fundi]

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

Looking forward to this

I just bought a Ti-Rant 9, Ti-Rant 45, M4-2000 a couple of weeks ago and I would buy a 762 suppressor and a 300BLK upper tomorrow if I could get a little more educated on the cartridge exterior ballistics.

If I was 25yr old I would be out getting an AAC Tattoo
No ink for me I think I'll spend my $ on guns, gear and ammo

[fixit69]

As if we're not asking enough... suppresed graphs with barrel length and trajectory, etc, etc, blah, blah...

Seriously, any info would be much appreciated, especially suppresed.

Thanks for the work you've done and the work you will do in the future.