AR40 feed issues

[newmexicocrawler]

Built her a .40 cal with a heavy buffer and a 308 spring and about every 4th or 5th bullet it will jam the breech and push the bullet in the case. These are 180Gr flat nose plated bullets loaded to the proper length as per Lee specs. My first thought is maybe the spring is to stiff and it is closing the bolt to fast, thought about cutting a coil or two off the spring to see if it gets better or worse. Anyone else have this issue if so what was your fix?

Edited July 13 by newmexicocrawler

[dwzuspsa]

check the entrance to the chamber.  Make sure that it is tapered going into the chamber.  Got a barrel from my brother, same thing was not feeding and the lead into the chamber was concave,  Put it on my lathe and tapered it into the chamber.