I have a Winchester Model 94BB rifle in .375 and my father has a .375 and a .38-55 barrel for his Encore (that’s a story).
Inn our experiences with TC barrels they tend to have short throats and abrupt origins to the rifling. Look down the barrel from the breech and you will see the rifling “standing out” visibly. This is not a very good description but what it means is the cast bullets must be seated deeper than you think to allow the barrel to close on a loaded round.
This abrupt origin to the rifling will generally give you problems with leading in the throat (and with copper fouling in the same area) until you sort out bullet diameter and seating depth.
In the TC’s we shoot cast bullets as large a diameter as will chamber – with most mold this means – as cast and either hand lubed, pane lubed or tumble lubed. In Dads barrels the bullets seated out to touch the rifling and as large a diameter as possible seems to work best.
Marshall has some good .375 Winchester bullets and they will probably be the easiest way to start with cast bullets.
Marshall has worked with the .375 Winchester a lot but has not written about it as much as we would like. This link will get you a thread with at least on good post by Marshal.
This thread will give you a little more.
This thread has some loading data and participation by a TC shooter or two.
This thread deals with reduced loads.
This thread has some thoughts on bullet sizing from Ed Harris that are worth reviewing.
Marshal and I have different thoughts on cast bullet hardness. Marshal has more experience and I defer to him on the issue of hardness. This is an informative thread.
Here is another thread with thoughts on bullet diameter.
This thread will give you a few thoughts on throats and barrel diameters.
There is not a lot of TC data here but it should give you a start.
If you have not seen Rocky’s articles on the .375 Winchester here is a link to it. For some reason my computer throws every thing to the right and I must scroll over to read the article. I have urged Rocky to put a Reduced Load article on his list of to-do projects. The .375 is great fun to shoot with reduced velocity cast bullet loads.
After you have experimented with commercial cast bullets be sure to try the 255-grain Lee cast bullet. This bevel base bullet is very accurate in our rifles and is easy to work with. We shoot it as cast and tumble lubed or hand lubed regardless of velocity.
I may have my links out of sequence but I believe you will still find the threads useful.