M4A1's usually use a 363mm long inner barrel.
I usually run a CQBR length M4 indoors and a full length M4 for outdoors.
Don't sweat 5-10mm here or there.
Personally...I'm a big fan boy of the Guarder clear hopup rubbers...they've just worked so well in so many rifles for me. I've seen, used, and bought a number of MadBull Black Python V2 tightbores. IMHO, they're a good value. Prometheus are super sweet but the price tag on them is horrifying.
Last edited by m102404; November 21st, 2009 at 22:31..