Well.... It all started when I contacted Dom about a Dictator with a can size bore. He said he could make me one of the golf ball size ones "over-bored" to can size, or a larger scale one with (IIRC) an 8" OD barrel. I opted for the GB scale model with a larger bore since the weight of the larger model would probably have put me in the hospital for lower back surgery. I already have a 260# Coehorn that doesn't much leave the garage anymore.
I came up with the idea to make a bore reducing sleeve for golf ball use, and Dom and I worked out the dimensions. We decided to leave it without any type of retaining feature - I figure I'll test it to see how well it works without one. It can be added later if need be. Also, it might stick due to fouling, so I might have to make an expanding plug that attaches to a slide hammer to remove it. We'll see how it goes.
The sleeve has an OD of 2.625" and is a slip-fit to the bore. ID is 1.730". Breech end of tube bottoms out ahead of the powder chamber and length is flush with the muzzle.
By the way, I've got to give Dom a 'tip o' the hat here - We exchanged multiple emails that no doubt took Dom a lot of time to answer. He was a gentleman through it all. I've had custom items made by outfits in the past where the person I was dealing with didn't seem to care to answer emails with more than a two word response. Dom addressed all of my concerns promptly, made suggestions, and worked with me to get my stuff made the way I wanted it done.