Will a Rem SP10 barrel fit on the Ithaca Mag10?
For what it is worth I have an old fixed choke Ithaca mag 10 and a newer choked tubed Rem sp-10 and they will not interchange. When rem bought the design and released the sp-10 in 1989 they indicated they redesigned the gun.
The bolt for sure was changed and the sp-10 has a teflon ring and a groove cut to help cleaning. Stocks and forearms are the same but not sure about anything else. Some say pending the serial number of the ithaca the barrels will interchange but I think that is BS and so does many others. I know with machine work a smith that knows what he is doing can make them fit.
According to Remington, "No." they will not fit
If you search their site it only says...
"Question
Will parts for the SP-10 work on my Ithaca 10 gauge?
Answer
Remington Arms purchased certain assets of the former Ithaca Gun Company, including their 10 gauge autoloader. We re-engineered the gun and introduced the SP-10 to the Remington product line in 1989.
Parts for the Ithaca Mag 10 and the Remington SP-10 are not interchangeable. The remaining Ithaca assets were purchased by Ithaca Aquisition Corporation, and they may be able to offer repair parts for your Mag 10."