I would recommend searching YouTube for some video tutorials. I first applied a few coats of CA to the barrel, then sanded to 1200 grit to get a smooth base. Applied the decal, (make sure it doesn't have to go over complex curves!), waited for it to dry, then applied a few more coats of CA to seal it before finishing and polishing. Obviously you don't want to put enormous pressure on it as you apply the CA, but it shouldn't lift.
One more thing - it may not be clear that after you have printed the decal you need to apply a few thin coats of acrylic lacquer to seal it, or else the ink will run while you are soaking and applying it.
