There was an article a year or so ago about a guy that built a 22LR reamer with a throat that tapered to 17 cal and one that tapered to 20cal. He was chambering 17 and 20 caliber barrels for the 22LR. When he fired them the bullet was swaged down to the bore diameter and the resulting longer bullet had more velocity and penetration was greatly increased. It was an interesting article but I can't find it in any of the magazines I've saved.
I think I read that the Germans did something similar with the .318 bores on their rifles so that they could shoot the newer .323 bullets. It seems that the long throat prevented the immediate spike in pressure and the bullet was swaged to bore diameter with no problem.
This is stuff that I have read and not anything that I have done. I would like to try one of those 20 caliber/22LR versions though, but I think the guy was in Australia and has since passed away.
All this is why I said that I would love to see a chamber cast of the 6.5 Arisaka that was rechambered to 30/06.
