magazines
Just read the post regards certain ammo not fitting in the SIG P220 mag. In the same post it is stated that the pistol also locked into battery with a live round. The post concludes with the statement that apparently the SIG will not feed everything.
Considering the ammo issues combined, I am strongly suspect of cartridges themselves. Locked into battery hints at either improper or lack of crimp, or a cartridge that exceeds overall length. A cartridge too long could also be the culprit with failing to fit in the magazine. I wonder, do the rounds that fail to fit in the mag display the same issue with all mags present? Othewise, the P220 in question has multiple issues, a bad chamber and a funky magazine.
My experience with my own P220 and some half dozen others that I oversaw, not to mention being present on firing lines and training where many other P220's/ammo combo's were in use, is that the P220 is extremely reliable and not finicky about what it is fed. I've even handloaded some big, blunt, 250-255 gr .45 LC slugs, and the P220 just gobbles them up.
One caveat is that the early, blued, dovetailed rear seam 7 rd mags do indeed seem to have a life span. I've seen more than one instance where removing said type from service and replacing same with the more recent hardback, stainless MecGar variety resolved a feeding issue.