hi
which is the heaviest cast slug which can be stabilised by 3030's 1/12 twist? there are moulds from 120 to 220 grain? would a 3030 stabilise a 220 gr cast slug at low velocity around 1400 fps?
regars
yes

I never tried a 220gr. bullet in the .30/30. I have used 180 and 190gr. bullets with outstanding success. My favorite 190gr. is an old custom job from Saeco. Three deep grease grooves,GC, flat point, base sized to .001" over groove dia.,nose sized to ride the lands. Cast from Lyman #2 alloy (or a bit softer- it doesn't seem to matter) and loaded to 1900 fps out of my 1927 vintage Savage M99A has been my standard deer load for a long time. It duplicates the old .303Savage load to a "T" and groups into 1 1/4" all day. For serious target shooting, cast from linotype and loaded over 15gr. 4759 it will go under an inch out of my custom Winchester M54 .30/30, w/20X Unertl. The same gun and bullet cast soft and breech seated using the same case indexed in the chamber with the same 15gr. 4759 will go far enough under an inch that you wouldn't believe me if I told you!

Both guns have 1-12" twists.

My best bullet in a 30-30 is a 190 grainer as well -- the Lar45 FAT 30 custom to be specific. Launched at 1650 fps with a full case of IMR 7383 she shoots 1 and a half inch groups at 150 yards (with most of that error being me, I am afraid).

30-30 Marlin rifles can shoot better than most folks give them credit for.

Oldfeller

My FAVORITE in 30-30 is a Saeco 200 gr GC bore rider (#308). It will chamber in my Stevens 325 but not the '94Win. Kicks harder, hits harder.

The RCBS #30-180-FN will cast out at 190 gr. in wheel weight metal with just enough tin to properly fill out the mold. Shootas good in several M94 Winchesters, a Marlin 336 and a strictly stock M54 Winchester. Work darn good on deer loaded to about 1950 FPS.
Paul B.