Sawed off or just short? With a semi auto, at leas a gas operated one as most are (not all though) you can't saw it off too much or the action won't work. You'd be safe as long as you didn't cut it down shorter than the forward hand guard or magazine tube. The length of the barrel doesn't really affect the spread of the shot much, if any. It's the choke, or lack thereof, that does that. Most short barreled shotguns, even the most "legal" 18.5" barrels (like mine), have a 'cylinder' choke, which means no constriction at all, same as you'd get by sawing off the barrel. Even my 24" barreled 'bird gun', has a 'cylinder' choke tube available, although all I've got is 'improved cylinder', 'modified' and 'full', don't think I've ever used the 'full' though. The short one doesn't have interchangeable tubes so you are stuck with what it came with, but for 'serious social purposes', 'cylinder' is fine. OTOH, I once hunted with a guy who had a Remington 870 with an 18.5 or 20 inch barrel with interchangeable choke tubes, who used it for bird hunting, just by installing the appropriate tube. (OTOH, another hunter in the group asked him if he was going to shoot pheasants or rob a bank with it. IIRC, he shot pheasants with it, at least one. :) )
Meant to add a thought about “sawed off” perhaps applying to the stock as well as perhaps the barrel. As you most likely know, overall length is restricted by the National Firearms Act, as well as barrel length. (to 26” and 18” respectively for shotguns, 16” barrels for rifles).
Owen said Adkisson concealed the shotgun in a guitar case when he entered the sanctuary, where children were performing the musical, "Annie Jr." Owen said Adkisson didn't say anything before discharging three rounds from the shotgun, which had a shortened barrel.
Because the semiautomatic weapon holds three shells, Adkisson had to reload after the initial attack. That's when several church members grabbed Adkisson and grappled for control of the shotgun. They overpowered him and tied him with belts face down on the floor, apparently disrupting Adkisson's attack plans.
"We found 76 shotgun shells," Owen said. The additional shells were in a black leather bag Adkisson had carried along with the guitar case.
"He expected to be shooting people until police arrived and he fully expected to be killed by those responding police," the chief said.