For those of you who have never heard of these you may find this informative.
I first came across one of these in the 1970's while on a deer hunting trip with an older gentleman at his camp along the Mersey River, not far from Kejimkujik National Park in NS. On day 2 or 3 of our trip we met up late in the afternoon at our agreed rendezvous and as we walked toward each other I could see he was carrying a freshly shot rabbit. I commented on how clean the rabbit looked, as the last rabbit I had seen shot with a deer rifle clearly show signs of severe over kill. So he pulls out a caliber conversion sleeve and proceeds to demonstrate how it was used to chamber and fire a pistol cartridge through a rifle. Well I thought it was just about the neatest gadget I had seen in quite some time.
In this case he had a Winchester model 94 in 32 special with a conversion sleeve chambered for a 30cal. pistol cartridge?? (as best that I can recall, I am not up on pistol caliber sizes).
This is a great way to get dual duty from your rifle for picking up the odd rabbit, dispatching nuisances or just some cheap plinking.
Further info:
https://en.wikipedia.org/wiki/Caliber_conversion_sleeveCheers