Could theoretically increase accuracy though unless you throw in a red dot in place of that short sight radius, otherwise you just get a short barreled PCC with all it's downsides. In full auto it'd still be worse than a proper SMG due to light weight, excessive fire rate, short barrel and balance. If the brace/stock folds and the weapon is compact enough to carry then it'd be a somewhat viable alternative to a big ass handgun in a powerful caliber like 10mm, assuming it's in full auto and fires something with less recoil than at least 9mm+p, being usable for things like <100m suppressive fire or something.
Because they, especially the round nose ones suck, and while they6 suck just as much as they did before we fortunately now have access to better options that suck less.
Then get a 45-70, 30-30 is not a huge step up from 357mag in a rifle, as other poster said, with better 357 loads rivaling weaker 30-30 ones. 45-70 is also easier to reload and works better on elk and above, something that both 30-30 and 357 somewhat lack.