Carbine Length Gas System

[LRRPF52]

Whats the shortest barrel length you can go with a mid length gas before you see cycling issues?

Depends on other variables, like the gas port diameter and the load. You could go 12.5" MLGS, with the port cut for your range of loads, and this has been done already by a guy who shoots it suppressed a lot. Unsuppressed, you're going to need the port cut correctly, and really watch what loads you shoot.