PolarFBear I've been shooting cast lead bullets in my three SKS rifles from three different countries of origin as well as ever other rifle and handgun I own for more years than I can count.
Both the Lee .312" 155 gr. SP with standard grease groove and .312" 160 gr. RN tumble lube bullet pictured below are gas check designs and were designed for the 7.62 x 39 cartridge. I have the 160 gr. which is a longer bore rider version and I find it to be the more accurate of the two. Load data for both those bullets can be found in the Lyman #4 Cast Bullet manual. IMR-4227 is one of the powders listed with both those bullets.
As to the Lee .312" 185 gr. RN there is no listed data for that bullet in the 7.62 x 39 cartridge but I've shot it in my SKS rifle for years. A good powder to use with the 185 gr. GC RN bullet is either IMR or H-4895, I like 24.0 grs. for a nice little thumper load, neither powder will go over pressure even with a compressed load, but 24 to 25 grs. is a good load.
If you are powder coating your bullets and using a gas check you can mix that wheel weight alloy 50/50 with pure lead and quench the bullet right out of the toaster oven after the bullet cures. GC,size and let them sit about two week to age harden, load and shoot away. I'm pushing bullet cast from the 50/50 alloy powder coated and gas checked up to 2300 fps. with no issues and excellent accuracy.
Like the Lee .312" 185 gr. RN the Lee .312" 160 gr. RN tumble lube bullet will do double duty in the Mosin rifles if it cast large enough. Powder coating will add a couple thousands to the dia, I size all my bullets for the SKS and Mosin rifles to .314" The Lee 160 gr. GC TL bullet will shoot very well in many standard US 30 Cal. rifles as well. I've used it sized to .311" in my 30-06 and 300 Sav. with excellent results. 16.0 grs. of Alliant 2400 is a excellent load with the Lee 160 gr. TL bullet sized to .309" to .311" which ever the larger dia. best fits your standard 30 Cal. rifle. The same loads is also excellent in the Mosin rifles as well with my bullets sized to best fit the throat of the gun.