To be honest, I have only used .451 bullets because I don't shoot .45 colt. and the required .452's. But if it is supposed to feed either then maybe understanding better how the collets work together will help you solve the issue. When I first got mine, it wouldn't feed .451's either. A little work with a dowel, wet/dry, and adjusting the die screw-in depth fixed it for me. Good luck.
Looking at the picture above (.45's but all calibers work the same), two things have to happen for the bullets to drop.
Reason1. The top collet (left in the picture) has to let bullets fall freely through it unless the fingers are pressed together by the bottom collet. If it doesn't, clean the inside good, sand any burrs if any, and pry the fingers out a smidgen with a dowel if necessary.
Bullets are ONLY supposed to stop in the top collet if a case is inserted into the bottom collet (right in the top picture) deep enough to open the other fingers in the bottom collet and drop the single bullet in the upper portion of the lower collet.
Reason 2. The bottom collet only opens wide enough to drop a bullet, if the bell is wide enough and the case is deep enough. To make the case deep enough you may have to turn the die in more.
The first thing you have to discover is where the bullets hang up....top collet or bottom collet. Top collet....clean it, deburr it, and/or rod it out a little if it has worked beyond where the springyness lets it return to open.
Hangs in the bottom collet? most likely the case isn't belled enough (.30" bigger than your bullets) or the die isn't screwed in enough.
Last picture shows how deep a .45 has to be into the bottom collet to allow the bullet to drop. Bullet shown in the top collet are pinched by my fingers simulating what happens as the case is pushed into the lower collet and in turn pushed collets together to pinch the top one. Hope this is of help.
