smg762 said:

Regarding l/d ratio, the FN 15mm had really long bullets for their APDS....look at the pics.

I did, and that is indeed a 5-ish calibre long projectile. And I don't remember that project being cancelled for something other than the sudden lack of a need for a weapon that outperforms .50 BMG but isn't an autocannon yet. That sabot is a lot bigger relatively than you'd want for an infantry weapon though.

roguetechie said:

...the good designs they screwed us out of...

Which good designs?

In terms of protectig from hard impacts, a CT could be good, but what about just havig an extremely long neck, and cramming the whole bullet inside it. 

Gettig a high BC is fairly easy because you can use a smaller caliber like 4.7mm and just make the bullet heavy ish. Like 48grains.

https://m.youtube.com/watch?v=qcvjBU_AEbQ

This is an obvious argument for velocity over bullet quality

Ok before i sign off heres my last bizzarre idea...how about a .22  (AR2 or FABRL shape)

 with 4 slight fins or extensions on the bearing surface.  This brings the caliber up to 6mm or 6.5mm allowing for extreme energies.  

Again these fins are just as long as the bearing surface so they support the entire bullet in the barrel.

Obviously you need a wad behind it to seal the gas. And i dont know how these bore-riding fins would interact with the rifling

FAL or AR-10. FN MAG, which we finally adopted..... after the problems with the M-60 were mostly fixed. That's just the 1950s.

Yeah, but in the 1950s, the Army was looking for a lightweight rifle and machine gun.

The FAL weighs as much as the M1, and the MAG is almost as heavy as the M1919A6.

Sure, the FAL and MAG were better than the M14 and M60 in some respects, but how did Springfield "screw us out" of them?

As for the AR-10, certainly it was basically a much better design than both M14 and FAL, but ArmaLite screwed itself with that.

stancrist said:

Sure, the FAL and MAG were better than the M14 and M60 in some respects

Stan, I believe that you misspelled "nearly all" as "some."

I realized that Textron / HK rifle is needlessly extended backwards. As there isn't backward extraction, backwards movement only needs to reach the base of the fresh cartridge.

Just look at Steyr ACR. Before I could see the internals, I wondered (during the 80s and 90s) how the magazine was so close to the buttstock. And here you are.

Recovery spring can also work against recoil and thus it needs a sizeable working lenght. But it could be placed elsewhere and save some lenght to the weapon, even permitting an innovation as novel and groundbreaking as a folding stock

poliorcetes said:

I realized that Textron / HK rifle is needlessly extended backwards.

A lot of bolt travel equals less bolt velocity before hitting the buffer and less "felt recoil".