How short can the barrel be? 20"? Between Jeff cooper, and Hemmingway, the idea of a short, bull barreled 505 Gibbs seems appealing...and the idea of a short bull-barrel 458 Lott makes more sense...

20" 458 WinMags have certainly been made. You should shoot one at night for best effect. Some countries have legal minimums for barrel length and you might want to check that before cutting it too short.

I like short bbled bolt guns my self.
Just stay away from ball powders.
I have a 19 3/4" 375 H&H I like a lot.

My 500 A-Square had a 21 " barrel and I liked it tremendously. The Gibbs burns A LOT of powder tho ,but no doubt you could get all the speed you needed. I have a 20" brl on my 458 Win and AA 2230 is hands down my favorite powder for it , but I use 4198 with the 300 gr bullets . Terry Wieland said that 21" [ i think ] barrels are effecient in the Lott and I will be shortening it to 21 " as that is for more handy and it still leaves room for a brake. I once saw a 14" barreled 460 Whby at Great Northern Guns : I think that would have been TERIFYING... Have fun .. gumboot out..

My first ever big bore was a 458Wm with a 20 inch barrel. I loved it for its handling capability and I could carry it all day without ever "feeling" it was in my hand. I was also much younger then I found that it shot just fine.

I believe Ryan Breeding loves short barreled large bores....