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McGowan or X-caliber HBAR carbine 1:11,12 280$ normal or 5 grove.
Took a while to get mine from McGowan (220$ IIRC and they put it together for me), several years ago but a good barrel. I chose 10 as I use 10o – 190gr so it’s general purpose – and the slowest I could find at the time.
Let’s add a twist. Larry uses 144k for the rpm threshold. IIRC he uses mostly #2 alloy. If you want softer alloy, you may want to go to the slower twist. Bama found he didn’t smoke the fast stuff if he added copper to the alloy. I used low Sb in my 1:8 pistol, pushed pretty hard and it worked, just Cu/Zn/Sb. All my moulds are essentially smooth sided so lots of bearing surface. So it’s not just stability for bullet length but fps & alloy too.