i dodn not meant the lenght of the box, i meant the broad...
(beware of uberXtreme Paintskillz)

The Holster is sized tot the gun to give it a tight grip. Would the Gun be nut so blocky and minimalsitic the Deathwatch guys would carry Leatherholsters i guess.
I've made the Boxes myself recently [ http://www.thedentedhelmet.com/f62/full-metal-deathwatch-2-0-a-46411/#post592661]
My idea is to put in some Foam or EVA of the Inside of the box to grip the gut solid, make it noiseless while walking (no clank and klonk front the gun wobbling for and behind). And to avoid scratches on the Gunprop when drawing and holstering.