FX M3 .25 jamming

My gun has always seemed to jam every now and then while cycling pellets. Probably 4 to 5 times every mag. It can be recovered each time with gentle jigging when closing the cocking lever, but it's getting tiresome.
Recently a friend was trying out the gun and was not as gentle. Got some lead jammed by loading multiple pellets. I took it home and cleared it but does anyone have some advice on this ? Think it may be a mag issue?