Mid-length gas system in the cold.

[Gargoyle]

The most functional and precise AR platform ejects brass to the 2:30 clean, and then to the 3:00 dirty. Past 3:00 is inviting problems. I believe Superlative Arms is the one to thank for civilians thinking 3:30 is optimum.

[Caduceus]

Obviously, a 14.5 with a 0.0625-0.0630 gas port will be up to military requirements . . .

But, most 16" mid-lengths I have will not reliably lock back when shot 180 degrees straight down, and these are the common available port sizes. That does not instill confidence if you start to factor in -20 degree performance.

Um.... wouldn't 180 degrees be shooting your own shoulder....?

FWIW, having shot in -20, no real issues, but limited to 2 carbines. And I haven't tried straight down, but with several new deer stands in new property, I'll be glad to try this winter.