kx59 put up a great summary, so I don't have to, other than to offer many thanks to the South Texas Gunblogger Community Organizer, Southern Belle.
I did learn a couple things. First, factory reloads can be "cool" loads (loaded with less propellant). Not really a problem there - it makes the ammunition a bit less expensive and it makes the round a little slower. I guess that it's possible that some ranges like that, although it probably doesn't make enough difference to tell.
However, your gun might care. Less propellant means less energy, which means that the recoil spring will compress less than it would on a hotter load. My 1911 had been having intermittent problems where the slide didn't return to battery (the firing position). It would once in a while stop about a quarter inch from where it would in a full cycle. Pull the trigger, no bang.
I'd been shooting reloads from a local Texas company that had been recommended. Back in Atlanta, I had short some reloads from Atlanta Arms, which is what the range stocked.
I was thinking that I'd need a gunsmith to look at it. But I picked up a couple boxes of white box, and it worked flawlessly. The white box rounds are hotter.
I guess I'll feed the 1911 factory new ammo from now on.
The second thing I learned yesterday is that shooting slings are like corsets: they both work only when they're good and tight. I kept tightening the sling every time I took a run with the Enfield, and think that I probably need to tighten it a bit more. But man, it sure improves your groups.