I read a comment in the Medium bore forum that commented a 1 in 10 twist 35 Whelen would need really hard bullets to work. I have an old 1903 Springfield with a 1-14 the cleaning rod says, and shoot the 1.14" 290 grain RN GC bullets very well at about 1900-1950 FPS using IMR 4759 31.5 grains.
I also shoot my 30-06 1 and 10 twist with the same alloy, 12bnh or so, 220 RN GC at the same velocity. No problem in either.
So why won't a 35 1-10 twist react the same way?
Would be happy to read your thoughts

Fury, it has been my experience that leading is more readily caused by bullets improperly sized to the bore, or inadequate lube, than by the rate of twist in a barrel. I am sure I could make even the best caste bullet foul a barrel if I push it hard enough... but at velocities below 2200 fps, I find gas checked bullets work well, and the barrels clean much easier than with copper fouling.

Mine as well sir. So still looking for "why not?"

I question that gas checks have any benefit whatsoever, except making $$$ for the folks selling them. I have shot .22 cal and my .243 at velocities above 2500 fps, no gas check and no leading.

i think the secret in running plain base bullets at high vel/minimal leading/good accuracey is to have bullets that are HARD BNH 25-30

Undersized 24bhn will fill the throat and bore with lead. Revolver shooters have proved this repetitively. Where plain based 12bhn that fits throats and bore work great. So fit trumps alloy every time I think.
Taking size fit out though; anyone shooting a fast twist 35 or so caliber with cast have examples? 2000 fps or so?

Didn't we find that the 'micro-groove ' rifling didn't have an accuracy problem ?. The problem was low hardness and too small in diameter bullets ?
And why would cast versus jacketed make a difference since that's a physics problem of stability of a projectile ?

Mete,
In my opinion, fit is almost everything and the last remaining part is some kind of "Cast magic" that us mere mortals only guess at. Some of the guesses are alloy and some are lube and some is how progressive the burn curve is and so on it goes. I just try to get a good fit with BHN 12 or so, Gas checks because It makes me happy, and lot's of lube, enough to leave lube stars on the muzzle, tuft of Dacron,( you can see that this all is where the Cast Magic comes in) and a velocity that will get me to the target from muzzle to 250 yards at hunting accuracy. Your other question: the difference in Cast and Jacketed is both Mass density and the fact that one can't easily add velocity to cast bullets in the stability equations. At least as I understood your question.