Magnum

I'm new to this site, hoping experienced folks here can help me. I have a Benelli SL 80 and need to replace the stock, but I can not figure out how to remove the current stock. I have the shotgun disassembled down to the stock, receiver and trigger assembly. There is no rod or nut in the butt end of the stock, so I assume the stock screws off, but it won't budge. Can anyone help? Thanks.