This is the point I tried to make earlier. Hard bullets may not deform to seal the barrel and thus permit gas cutting. I have pesonally run Cast Performance gas check bullets out of my FA to a velocity of 2019 fps without leading in the barrel. As I said before, I'd try several different brands of cast bullets and see what your revolver likes.

I've never seen a 44 that wouldn't "lead up" when driving a lead bullet that fast.

If you find one that won't please let us know.

Using gas checks might help.

$bob$

Cast hard, properly sized & lubed, you can drive lead bullets up to 1200fps w/o leading or gas check.

LD, not so, I never have a speck of lead from my Rugers with 320 to 330 gr boolits and heavy loads of 296. My new BFR .475/.480 does get some lead in it. Hard to explain as velocity is similar except the BFR uses 400 gr boolits. I use hard cast the same size as the throats. I also use nothing but Felix lube.
I shoot a lot of light loads for fun and never have more then a small particle of lead on a patch.
Sometimes, a new barrel needs to be shot a few hundred times with jacketed bullets first, cleaned good and then cast boolits shot. Smooth em up first.

Montdoug - when you say 10.5 grains of Unique is a little much, do you mean a little much for cast or are you implying I am pushing the safety margin? I consulted my 3 loading manuels (Hogden, Lyman, and Lee). This seemed to be a upper mid-level load for Unique. Not max.

I recently loaded up some 44 special loads with this same bullet with (5 or 5.5 grains Unique - cannot remember off-hand) and I got leading with these as well. The leading appears in the first inch or two of the barrel. I guess I have a non-lead friendly barrel. I'll just shoot up what I have loaded and try the 270G GDSP.