I have the classic Keith bullet, in both flat base and gas check, for each of 357 and 44 magnum. I had shot so many 30 caliber cast bullets at quite fast speed, that I didn't really think a gas check was needed for the revolvers.
In the 30-06, I found that overloading the cast bullet resulted in very erratic groups. In the spring I found many of the bullets I had fired in the winter. Quite the odd one had a groove down the side of them, where the gas had escaped. Even the gas check ones. This was obviously the cause of the flyers. There was no increase noted in lead fouling with the heavy loads. Maybe there would have been if I had fired a lot of them. But when accuracy went, I cut down on pressure.
Thus, I always thought that if my revolver loads were accurate, that is all that mattered. Accordingly, I think if they chronograph with a normal, to smallish extreme spread, they should be accurate.
In my notes I see where 13 grains of 2400 in the 357 Smith, with a 168 grain flat base, chronoed at 1335, with extreme spread of 59, for five. This is certainly not excessive for a revolver!
12 grains of H110, with flat base, gave 1124, with 60 fps spread.
13 grains of H110, f.b. gave 1152, with 68 spread.
12 grains of 2400, f.b., gave 1277 and spread of 48.
13 grains of 2400 in the 357 Smith & Wesson, 168 grain flat base bullet, with 38 Special brass, went 1247, with an extreme spread of only 28 fps!
I have similar results with the 44 Magnum, shooting a Ruger Super Blackhawk.
22 grains of 2400, 252 flat base, Lyman #429421 bullet, went 1415 with a spread of 68.
20 grains of 2400 went 1312, spread of 41.
Apparently,none of those loadings suffered from excessive load of a cast, flat base bullet.
My best ever minimum spread was with 8.2 grains of W231. The 252 flat base went 1018, with a spread of only 17!
My best ever five shot group, fired in a 7½ inch Ruger, rested on a bench, was a 1¼ group at 50 yards. This is an honest, no bs group. The load was 20 grains of H110.