Some time ago I shot a box of Remington 158 grain LRN 38 Specials and then a box of UltraMax 158 grain SWC 38 Specials. The UltraMax loads were far dirtier than the Remingtons -- actually, even much dirtier on outside of gun and on hand than powders like Swiss FFg and 777 FFg. The UltraMax has hard cast bullets with hard wax lube. The Remingtons have swaged, soft lead bullets with Remington's famous "dirty hands" lube.
More recently, I shot two boxes of 38 Special reloads, one loaded with Remington 148 grain HBWC bullets over 2,8 grains of Green Dot (maybe 800 fps) and other with 158 grain Speer swaged 158 grain SWC HP bullets over 6,5 grains of Blue Dot (probably over 900 fps). Far less powder "dirt" on my gun and shooting hand than from UltraMax, especially with the Speer and Blue Dot load. Both bullets are 0,358 and there was no leading in bore or cylinder throats. Neither bullet will fall through throats and all 5 throats appear to be very close in ID.
I have used lots of Remington and Speer swaged bullets and never get much powder "dirt" on hands or gun, although other loads have been cleaner. I expect that my current 38 Special reloads will get even cleaner as chamber pressure goes up, especially as I push Blue Dot "FBI" load as far as it will go without leading. Will not be able to go that high with Remington HBWC bullets.
Niklas