Jim B. I have used chamber adapters from Ace Dube at MCACE for a number of years and they are just great fun and worth your while.
I started with a 30 Luger and 30 Mauser/7.62x25mm Tok for a rem 788 in 308 and had a lot of fun. When I sold the rifle the adapters went with it and I picked up the same adapters for a 30-06 plus one for a 32 acp for the 06. Great garden rounds for pests around the house. You can handload those cartridges for a sub-sonic effect and still have a fairly hard hitting pistol round from a rifle barrel.
Even though the 06 is a 308 bore and both the 32 acp and the 30 Luger are 310 bore, they work just fine. The 7.62 Tok round from the adapter in my M70- 06 is pretty hot. I used a commercial hollowpoint to take a racoon at about 25m and it was verrry effective.
Some folks used to call chamber adapters 'sub-caliber' devices - whatever term you wish to use, they are effective, cost efficient, allow you continual easy practice with a big bore hunting rifle and offer a lot of fun and entertainment. They are also a very effective means to train new, younger shooters to the rifle. HTH. Mikey.