The problem is the ammo. Sorry but Glocks weren't designed to have hard cast bullets shot thru them. I'm honestly supprised your not having more malfunctions using cast ammo in your glock considering the tight tolerances of glocks barrel and chamber. I see that double tap is advertising velocities tested thru Glocks, but I don't believe they actually tested using a glock barrel. The chamber tolerances are pretty tight, and you'll find cast bullets are typically larger than jacketed bullets with some variations that are probably causing your malfunctions. The two solutions I have are first, NEVER NEVER NEVER shoot a cast bullet thru your glock barrel, so get an aftermarket barrel. Or second, and probably the best choice for reliability, just change your ammo. There are plenty of decent ammo's out there which would be suitable for a pack handgun. Personally I carry a Glock 20c with a 180gr Buffalo Bore JHP ammo. It spits out a little over 1320fps. As far as I calculate that hits well over 750ft lbs of energy. From what I see thats similar to the standard load ballistics of the .41magnum out of a 4" barrel.