Bevan King barrelled up a 375-06 for me about 35 years ago. We were talking about it again, when I visited with him last year. I bought the reamer and the barrel, and he did the installation and the chambering. I formed the first cases by necking up 30-06 brass in 338 win mag dies, then 358 Norma, and finally 375 H&H. They were a little wonky, but they worked.
Sent three fired cases off to RCBS. Got a custom die set back about six weeks later. They cost me $55, landed in Whitehorse, with two expander buttons, one tapered from 308 to 375. Those were the days..............
It was a a very fine round with good bullets, and actually shot much flatter than you might expect. It took some sorting out, but I finally settled on the 270 Win Power-Point ahead of a case full of H375. I killed a lot of really big game with that rifle. Gave it to a friend of mine and he is still using it.
Bevan still has the reamer, and a 375-06 Ackley.
Ted