If I remember right it's just a screw on top that holds the breach.
If so here is what I would do
Go to hardware store and find a longer screw, wing nut and normal nut. Screw wing nut all the way on the screw (so wings are facing up when you screw in on the marker) screw nut on next to hold wing nut secure (loctite all if you want)
On the field, unscrew wing nut, flip barrel/breach, screw back down, make pew pew noises
Disclaimer: I have worked on a hammer 7 but do not own one so I am going from memory on how the breach is held in