11" and 12" barreled uppers. who were they made for?

[KalashniKEV]

10.3" with a closed linear brake like a Troy Claymore or Noveske Pig would seem to make up much of that 40% dwell time.

While adding unnecessary weight and length... and removing the option for mounting a suppressor.

No thanks.

[Trajan]

While adding unnecessary weight and length... and removing the option for mounting a suppressor.

No thanks.

If you added a can, you wouldn't need such a device anyway.

[uffdaphil]

If you added a can, you wouldn't need such a device anyway.

Not an option in can-free MN. The weight and length is worth it here to throw the blast forward. If I didn't have so much family here, my retired butt would reside in can land.

[morbidbattlecry]

I've always wondered myself where the 12.5 ever came from.

[TehLlama]

The 12.5" allowed a bit more velocity especially with Mk262, even allows for some creative M203 Mounting applications (e.g. DD GL/SSC RIS-II) . For a civilian SBR with a good SS barrel, this has all the accuracy and the majority of the reach needed, and with a compact can on it it's still on par with a 16.1" with muzzle device for length. There are plenty of uses for a 12.5" carbine, and if for whatever reason I could only run one 5.56 weapon system, it would be a 12.5" with a 5" suppressor, A5 RE/buffer, and low powered variable optic.

[scottryan]

11.5" is the standard length for a short sbr since the 1960s.

10.3" is the length of a MK18 barrel.

11.5" is superior in almost every aspect to 10.3" if using a full spectrum of commercial and military ammo.

10.3" MK18 were specifically developed to give the shortest possible gun tuned to M193, M855, and Mk262 NATO loads.

[KalashniKEV]

If you added a can, you wouldn't need such a device anyway.

Yes, but for running short and running loud, the conservative options are:

1) ~11.5" for a healthy dwell time plus muzzle device/ mount of choice
2) <11.5" plus a booster... which is longer than most mounts, heavier, and negates the ability to mount a suppressor

It's clearly advantageous to have the extra barrel vs. a booster.

I've always wondered myself where the 12.5 ever came from.

12.5" is my favorite length... although I admit even indoors I don't "feel" the difference much between 12.5" and 11.5"... and even less between 10.5" and 11.5".

You're just giving up velocity and pushing the limits of adequate dwell time.