I kinda like the sound of "rifle crank" but some may think you're refering to a bolt handle or some other mechanical part. "Gun slut" works for me but everyone isn't as secure in their maleness as am I. I think "looney" refers to the odd little water bird that makes silly noises. Show a rifle looney a custom piece and I think you'll see just how appropriate that appellation is.
"Of all tyrannies, a tyranny sincerely exercised for the good of its victims may be the most oppressive." - C.S. Lewis
