[GaryCrow]

Follow the money. The cost to switch this completely will make someone(s) very rich. Whereas the transition to 300 blackout by changing only barrels and magazines would not enrich some retired generals yet be a much more viable transition with much reduced recoil and barrel lives.

Wow.

Do you realize what the range of a 300 blackout is? I hunt deer with a suppressed 300 blackout so I can tell you....about 80 yards. Beyond that it falls apart and is practically useless, yet you want to replace the entire inventory of infantry rifles with it? I want to be on the side of whoever's fighting you when the next war breaks out.

The 300 blackout kicks about the same as the 5.56, which is practically none in either case. Barrel life is a non-issue, if you can wear out a 5.56 barrel or a 300 blackout barrel then you've shot 1000X more than the average soldier will shoot in his career. I'm on my fourth 22-250 barrel after shooting untold thousands of rounds at prairie dogs and it's not particularly a barrel burner round. If you want to wear out a barrel load a 220 swift to the hilt and shoot it until the barrel almost glows. You're not going to wear out a chrome lined military M16/M4 barrel in your or my lifetime, and I doubt anyone will be able to wear out a barrel of the new round. It's a non issue.

[Myrddin]

I built a custom 300BLK SBR with a 10.5 inch barrel because the powder is fully burned at 9.5 inches. The 10.5 barrel leaves room for a suppressor when shooting subsonic rounds without being too long. Picking the right gas block position is also finicky. Supersonic rounds make plenty of gas for the carbine gas port, but the subsonics do better with a pistol gas port placement. I built with the carbine gas port since those barrels were easily sourced in 2015. I can buy an off the shelf upper today, so no need for a custom build.