MFfan

I see yours was made 1933-34 by the Connloyalist website. That site has alot of valuable info for you on this case.I have been researching my Gretsch Patfinder long cornet, as it would not tune with a standard trumpet mouthpiece. I learned the leadpipe was configured for a short shank cornet mouthpiece. I now use a jet tone Al HIrt cornet on it, with wrapping of electrical tape , and it plays and tunes fine now. There was a Conn 2 short shank just on ebay that sold about for about $12.00. The regular Conns have writing around the top part and a ridge at the middle of the shaft. The shortshank ones have no ridge and writing down the side of the shank. This may be the problem with your tuning. I believe that they changed to long shank in the 50's. All this info, photos, etc are on the Connloyalist web site. You didn't mention what model you have. Hope this helps. I don't know what MP was standard, but it looks like a Conn 4 is the most likely, like Bach 7c.