What's the best powders to fill the case full safely for the 45lc & 357 magnum rounds?
I hope to make a bunch in 2018!happy new year and happy shooting and have fun!

WW-296 or H-110 for max velocity loads.

If used In the 45 colt, ONLY use in Ruger BlackHawk or RedHawks. NEVER use in New Model Vaquero or Colt SAA clones.

If filling the case is your priority, take a look at IMR4227. It will not give quite the velocity of H110/296, but it is rather bulky.

For plinking loads it is pretty hard to beat Trail Boss. I use it for all my 45 Colt loads. I think I get around 750 fps with a 250 gr bullet in a 6.5" barrel. I would expect similar in the 357 with 158 gr bullets.

For max speed in the 357 I would use those already mentioned.