I never used acetylene, but oxygen and propane-butane mix (ordinary gas mix) I use for about 15 years for CoCr, so for partials and metal-ceramic bridges.
i have no trouble casting chrome with oxy-acetylene. Follow a few simple tips and it is trouble free. --Always use enough clean new alloy --keep tip of casting torch clean by use of fine sandpaper and thin wire for cleaning orifices. --use a clean flame which does not produce carbon into alloy, (adjust torch till small inner cone of flame is almost non-apparent)
--fatter flame is better than long and fast flame which could overheat the alloy cause uneven heating or burning.
--know the temperature of alloy from color and temperature/intensity of flame from sound
im having trouble getting enough heat for 3 or 4 ingot of co-cr. using oxy propane and size 15 cutting tip. thinking of buying larger cutting tip maybe size 32?
I use a multi-orifice tip (11 holes) propane set at 5 lbs. and oxy set at 10 lbs. I use Harris products. Don't buy this stuff the a lab supplier, go to a welding supply house, it's pretty light so you may have to tell them your are making jewelry so they get it.