I have to put the pellets with my fingernail into the barrel. The diameter of the Pellets is very larg (but not messure it sorry). shot pattern in a spring 10m 175m / s 1/2in
To answer your question, the H&N Sniper Magnum should shoot well from a Smooth Twist barrel. You see, FX makes the very same cylindrical pellet as the H&N Sniper Magnum but it's re branded as the FX Smooth Twist Pellet in 18 grain.