I had also wondered if the magazine sat high enough, which leads me to another question. After inserting the magazine and feeling it click into place, there is still a little vertical play in all the mags. I assume that is normal. However, again, the feed problem is usually with the first two rounds only. Thereafter the remaining feed fine. I will have to measure the ramp and see if I can find someone with another .45 Colt to trade out parts.
This sounds like the classic nosedive
problem caused by he mags not sitting high enough in relation to the feedramp, especially as you descrive the problem occurring mainly on the first two rounds. As far as your question about play in the magazines, I'd say a little
vertical play is normal but definitely not a lot of it. Most of my guns lock up pretty tight with little or no movement, and if you're experiencing a fair amount then that might suggest a worn mag catch is the culprit. If you do end up changing the catch, a cheap solution to the nosedive problem is EGW's high mag catch which is designed for the purpose of holding magazines higher in the well. I've put these on a few RIA guns and found they eliminated feeding problems with virtually all magazines. YMMV...