To be clear, I've done no research, just missing my TAC-13 and figured I'd ask around for options.

There's no factory SBS barrel as best I can find so a factory 18.5 would need to be cut down, but I'm not clear if there would be any effect on the gas system; I can't recall the location of the ports on the barrel. Next would be to just use a magazine cap, or a shorter extension.

Essentially, would it work you think? PFA

Its been done before, more than once (making a 930 SBS)

With gas operated guns that have the ports at the mag tube ring like (930, 1100, etc) shortening the barrel can often lead to functioning issues with lighter loads. Maybe someone will come along and tell you if any gas port or other adjustments were needed for reliable cycling on their 930

Steve, thanks very much.

cotton branch Customs would be a good one to reach out to.