I ask as I have several Bullseye 1911s I use for competition and the slides are very tight on the ones worked over by Bullseye gunsmiths. My used M52-2 that I bought from an older Bullseye shooter has a slide that is almost as loose as the slide on my 2012 Colt Gold Cup I use for Service Pistol competition. Granted, slide fit is less important than barrel bushing and lock-up for accuracy.

Were M52 slides lapped to the frame or machined for a production line fit? How loose are most M52s?

I would not classify the fit of my 52-2 slide as tight, but the gun is amazingly accurate. Back when I was building competition .45s,I
had a tool maker make me a steel block that I would put inside
the slide, then put the slide in a press. I then used valve grinding compound and a rubber hammer to lap the slide to the frame.
This usually took 1-200 hits, back and forth.
I believe, but don't have any facts to back it up, that all 52s were hand fitted. You don't get the quality in that gun on a production line.