I sent my 28" 870 barrel off 3 years ago. To have the barrel cut down to 21", have the forcing cone bored out, and a custom choke built to shoot long beard 6s cost me 115 bucks if I remember correctly with the bulk of the money being the choke. I think a barrel cut is like 35 bucks. If I was you id go ahead and do the whole shebang. Its worth it and in my opinion very affordable.