I normally play on two different trombones during the High School year. In the Fall, I play a small shank Holton trombone for marching band. The rest of the year I play a Bach Stradivarius. However, I noticed that going back in forth between the two insturments with two different mouthpieces is not super good for my lip. I was wondering if there was such a thing as a mouthpiece adapter that I could purchase so that I could use my Bach 4G megatone mouthpiece on the small shank horn? If so, where would they be sold?

Mouthpieces are designed and intended to work with the instrument.
So, using your larger mouthpiece on the smaller horn with an adapter
will present problems.

What I have done with my college trombone students is find the mouthpiece that works well with your horn. Then find the mouthpiece rim you like. You can then send the the mouthpieces to Bob Reeves and he will make the rim you like screw onto the mouthpiece for the other horn. You will love it!! And the cost to do it is like $40 (plus the cost of the two mouthpieces. Turn around is two days. Again, you will love it!!!

Example: I have a student who plays Bass Bone for college Orchestra and Tenor for Jazz. She plays a Bach 1.5G on her Bass bone. We took the rim of a Bach 1.5G and put it on a the body of a Yamaha Peter Sullivan tenor mouthpiece for her tenor. She is very happy with the mouthpiece and finds it easy to switch between the two intruments.

http://www.bobreeves.com/company_info/contact.htm

You play on a Bach 4G, you could just get that same piece for small bore. I didn't see the 4G on a quick search of WWBW and Hickey's, but Hickey's did have a regular 4 small bore. Still has the same rim size which is what you are concerned about.

I don't think you'll find a Megatone either, but that's not as necessary on a small bore.

In the end, you just want the same rim size. The backbore needs to be different for the different sizes of horn, and the depth and shape of bowl will be slightly different to give you the desired different sounds on each horn. (The G just means deep cup, still has the same rim) But, the rim being the same, you won't have the chop adjustments you're currently dealing with.

Okay, thanks

I have the Bach Megatone 5GS which is the small shank version. I think your best option would be to just get the small shank version of what you have right now. Obviously they make the 5 in small shank so I wouldn't be surprised if they make the 4 in small shank. Just do some searching for it. If you can find it go to a music store and ask if you can order it. It might be one of those types of things that no one caries because it's rarely purchased, but they can still order it.