Twist rate question

Perhaps due to a touch of madness, I've decided that I'd like to build a monster .58 caliber pistol for use with 300-450gr conicals. While looking into twist rates, I've noticed that a lot of modern sidelock pistols have what would be considered an extremely fast twist rate; around 1-20, yet these tend to shoot round ball AND conicals just fine, despite conventional wisdom to the contrary. Meanwhile, the M1855 Pistol Carbine pretty much did what I'm setting out to do with a much slower 1:48 twist rate. Currently, I'm thinking that overstabilization causes less problems than understabilization, but I'm still in a great deal of confusion and was wondering if anyone could point me in the right direction.

I shoot a 50 cal TC Scout pistol from round ball all the way to a 600 gr conical. So many variables to say I like one or the other yet other than the 600 is not going to be used anytime soon again. Not much info on my gun, but from what I can determine it appears about a 1-12 twist. I don't care for round ball except in my long guns of course. Do your homework and be very careful to be sure your gun can handle what you want to shoot through it. Mine can, but it's not your typical bp pistol.

Try this site:  https://thebarreloutlet.com/twist-calculator/

I have a T/C Encore barrel that I cut down for a pistol and it has a 1:28 twist (50 cal).  I shoot 80 gr of Pyrodex or Alliant Black MZ and a 300 gr Hornady XTP. in a Harvester sabot.
My .58s are really fun to shoot and recoil ain't bad at all but I'd imagine a .58 with a fast twist shooting a heavy conical would be pretty punishing on both ends.

Thanks Bronco22000 - That twist rate calculator answers a lot of questions I had on twist rates but still a bit confused, does the barrel length make any difference as I wouldn’t think it would but my 1858 Remy has a fast twist rate and shoots round balls fine .. Anyway it’s pretty cool to play around with that calculator ..!