I have a strange thing with my .475 in that using 2 boolits of the same diameter and alloy but one with a gas check and one without ( the gas checked boolit is 10 grs. heavier.) I can load 2 or more grs. of powder with the plain base without sticky cases but will max out sooner with the gas checked one. I have not had a chance to chronograph them together yet because it is just too hot outside and it makes the gas checked boolits stick more. I only have 3 of them left, having shot them in cool weather when they were OK. Using 296. Backing off 1/2 gr lets the brass fall out of the gun.
I have gone to 29 grs with a plain base 414 gr boolit without pressure signs, but at 26.5 the gas checked one will stick a few out of a cylinder full.
Only thing I can figure is it is sealing better.
Both boolits are a very close fit to the throats.
The amount of leading is the same for both too but it just pushes out with a tight patch, not sticking in the bore. Once I push it out, I can not find a trace of lead left in the bore and no way of cleaning will reveal the slightest speck. Shooting the gas checked boolit after the plain base will not remove the lead either so I don't worry about it. Accuracy doesn't suffer any from the small amount left in the bore.
Going down to the .45 and .44, I don't get any of these problems or leading even with heavy loads. Seems to be just the .475.