CZ 550 Safari Magnum. Came with two headspaced barrels but no magazine box. I installed the 458 Lott barrel. I bought the only magazine box I could find from CZ, one they call "Magazine Box 550 Magnum .375/.416".

Loaded up some dummy rounds with Hornady 500 grain round nosed SPs (not the DGS) seated to the cannelure.

Initially, the follower was hanging up but I stiffened the spring by bending it--a trick I learned from a gunsmith--and that was resolved.

The issue now is it will only feed two rounds from the magazine. The third jams against the feed ramp. The magazine box is 3.850", the loaded rounds are 3.640".

How do I fix this? Different follower, magazine box, polishing? Something else?

Hate to say it but you are too close to Wayne at AHR to not just send it all to him. With twonbarrels, I'd let him figure it out. I solved what was thought to be a feed rail issue with a follower change. Point being sometimes the solution ain't obvious.

It's going to stay a 458 Lott, though I am not opposed to sending it out. Not sure AHR would want to just tweak the feeding.