Tightening the jack screws on the bottom lock everything up nice and tight!
I see some mentioning of putting material between the set screws and barrel, I don't recommend this, as you want the set screws to bite the barrel a little so they lock in there.
I've heard rumors that these battle axes wear their "battle badges" proudly. The Chaos Quad Rail installed on this Com-Bloc noob's Vepr-12 with no notable problems whatsoever, and she hasn't even come close to breaking her maiden yet.
Concerning the jack screws, what say you about Loctite? Red or blue?