375 Winchester and Starline 38-55 2.125

[Leadmelter]

With 375 Win brass getting scarce, would the Starline brass trimmed back work in a TC Contender?
Leadmelter
MI

[No_1]

There should be no reason why it should not. Just be careful with the loading in case it gets in the hands of someone who owns a vintage 38/55.

[fryboy]

Check your chamber length, I have a carbine barrel that doesn't need trimmed yet the pistol length one has to be
Starline doesn't state that the brass is quite as thick as 375 brass but they did sort of imply that it's stronger than most commercial 38-55 brass, I've not crowded the upper spectrum with it ( more along the lines of 38-55 loadings as opposed to 375 loads ) but I do tend to run it warmer than reformed 30-30 type cases )
With my pistol barrel I haven't had to turn/ream the necks ( yet ) but it wouldn't hurt to check a few as you go along

[BCRider]

The .38-55 brass is quite a bit thinner a wall. So the fit in the chamber will be pretty loose. And you can expect to need to size it down that much further so it'll be a heavier pull at the sizing station.

I know all this because I've got an oddball size combo .38-55 rifle that has the smaller "early" bore size combined with the later "larger" chamber size. I'm using .375Win brass as an aid to filling out the chamber while still getting enough neck tension on the smaller .377 size cast bullets.

And due to the shock of the higher pressure and amount of stretch it'll have I'm going to guess that it won't last as long before it splits. But you should get a few firings from it.