It's not a bad idea, but since you already have a rimfire bbl, I'm not sure what you gain. I have a Bullberry Bee barrel, and I wouldn't trade it. But I also wouldn't seek one out.
Faster twist than 1:14 not required with cast bullets. I have Lee Bator mould that casts 55's, and they stabilize just fine in the Bee at rimfire speed, sans gas check, in re-smelted range scrap alloy. In fact, they shoot more accurately than my rimfire. Since I have the stuff already, they are cheaper to shoot than rimfire, and I get about 12-1250 out of a 55gr slug. Titegroup, Unique, Red dot, Blue dot, Clays, all work slicker than cowshiit for what I've described. Charges 3-5 gr w/o gas check.
I only have the Lee mould in 22 cal, but with a gas check and harder alloy, like coww, you can step on it a bit. Quench them, and step harder. So far, accurate loads have barely gotten to 2k with Unique and BD, but I've not experimented much, and haven't hardened the alloy further.
This is not a bad bugout set-up, as 5000 cast up and tumble lubed is about 40 lbs. Still have to have powder, dipper, priming setup, minimal sizing, etc. Casting equipment and a couple hundred lbs of lead feels good to own when I ponder the future availability of components.
