[ezypikns]

I've got a whole bunch of Lasercast 250 gr LRN (.452 dia.) bullets left over from cowboy loads for .45 LC. This may be a dumb question, but is there any reason not to use them in .45 ACP cartridges?

[BattleChimp Potemkin]

You can but have to be careful on two fronts (as I have):
1. Powder capacity: Not only is the case capacity reduced to keep the OAL okay, one is using lead. Go too nuts, its a quick way to get pressure problems. Try to keep them around 750 fps or lower. Its tempting to get them fast, but pressure builds up quick (chronoed some of mine at 800 fps, started popping primers).
2. Feeding: Some guns like it, some dont. Also, a higher poundage spring keeps things bounding okay.

They are usually very very accurate at 25 yards, not to mention giving you huge penetrating power on game. I could see these as a pig load :D. Disclaimer: This is my load, YMMV. I use 4gr. of Titegroup at 1.190" for pin load, that or Vihtavouri 3N37 for a heavy ball, low flash load.

[Walkalong]

I have shot a lot of Ranier 250 Gr TrFP's in .45 ACP. No problems. W-231 was the powder for most of them, but many will work. 800 FPS is plenty with them.