Thanks for the detailed answer.

In short: life is compromise, and one has to make the optimal choices based on one's needs.

And as Stan points out, mag lenght is important in ergonomics, especially for warfighters with smaller hands, and for storing, for all warfighters.

Being a little pickier: do you have any idea how much volume is lost when using poly cases?

What I would find interesting is a 7.62 round based on the existing case for a longer ogive projectile. Either by dropping the length of the case to about 45/47 mm and perhaps using a rebated rim case like the .284 winchester. Your .224 scaled up to 7.62 is looking around .27 and 9.8ish grams. An MV of 840 mps should be practical with the larger case at least. 

stancrist said...

M1 rifle, 24" bbl; M1919 machine gun, 24" bbl

  M14 rifle, 22" bbl; M60 machine gun, 22" bbl

  M16 rifle, 20" bbl; M249 machine gun, 18" barrel

  M4 carbine, 14.5" bbl; M249 machine gun, 14.5" bbl

Others you left out:

M16 rifle, 20" bbl; M60 machine gun, 22" bbl

M4 carbine, 14.5" bbl; M240 machine gun, 24.5" bbl

M4 carbine, 14.5" bbl; M249 machine gun, 18" bbl

H_Minus said...

stancrist said...

 M1 rifle, 24" bbl; M1919 machine gun, 24" bbl

  M14 rifle, 22" bbl; M60 machine gun, 22" bbl

  M16 rifle, 20" bbl; M249 machine gun, 18" barrel

  M4 carbine, 14.5" bbl; M249 machine gun, 14.5" bbl

Others you left out:

M16 rifle, 20" bbl; M60 machine gun, 22" bbl

M4 carbine, 14.5" bbl; M240 machine gun, 24.5" bbl

Omitted because they're apples vs watermelons nonsense.  Need to compare weapons in the same caliber.  Otherwise, you could take such silliness to extreme, and compare 5.56mm M4 to .50 M2.

H_Minus said...

M4 carbine, 14.5" bbl; M249 machine gun, 18" bbl

I doubt those units which are "pure fleeted" with M4 carbines use 18" barrel M249s.  You're just arguing for the sake of arguing.

stancrist said...

 

NathanielF said...

...the light 85gr bullet satisfies the Army's requirement for a round that can be used in training ranges. The Army has shown that they will accept combat rounds with lead cores (e.g., Mk. 262 being used outside of SOCOM) as long as those rounds are not being used for training. Great, so here's where you cheat. If more range is desired, additional loads can be introduced or brought out from stores that have heavy, lead-cored bullets in either OTM (for DMRs) or steel-jacketed FMJ (for SAWs/MGs) bullets to meet those additional requirements...

The problem with the above idea is that the Army has shown they want only one round for both training and combat.

 

NathanielF said...

This does mean there would need to be additional suites of tracers, etc...

Same problem as above.  The Army wants only one standard tracer, etc, round.

 

Yes, as mentioned in the OP, I am cheating known requirements a bit. The proposal shouldn't be taken too seriously, therefore.