I use Teflon in my smokeless hunting rifles for small game rounds. I cast from wheel-weight metal, and wrap them in one turn of "gasfitters" tape (not the thin, 1/2" wide, hardware stuff).
PTFE THREAD SEAL TAPE MIL SPEC T - 27730A 3/4" X 520"
I do not size, either before or after wrapping. My load is Unique, Universal, or Herco, from 8 to 11 grains. I top the powder with a pinch of teddybear guts, to hold it against the primer. Velocity is in the 1200fps range. They usually group at the tip of the lower duplex post in a scope at 4 power.
The advantage for this use is that neither the cast nor the jacketted bullet fouling destroys the grouping of the other round. The NRA cast bullet project found very early on that jacket fouling and Alox lube fouling were incompatible. The use of Teflon is neutral in that respect.
I have had very little experience with higher velocity loads. BTW, I learned about Teflon tape from a Mike Venturino article from about 1976.