Modern manufactured ammo is readily available and is not going to be an issue until the factories shut down.
You'd spend a lot of time and money rebarrelling the T44 and for no reason or utility. If you're concerned about ammo availability, get a reloading outfit and make all your calibers.
As far as a conversion goes, I think you could make it into a pretty nice .405 or similar, but why bother?
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