...have lots of Win 231/HP-38 any down sides to using it in the .45 Colt pushing a 255 grain bullet at 850 fps?
No problem.
I've loaded 250gr cast lead bullets with W231/HP-38 using Hodgdon's load data, and they were very tame, even with high book loads. Here's a link to a thread on it:
https://www.24hourcampfire.com/ubbt...671/45-colt-new-target-load#Post14820671