Well, from 'days gone by', the choke was only at the last couple of inches in a fixed choke barrel, and it helped to squeeze a shot charge into a 'given bundle'.
The choketube will do the same thing. It's putting some constriction in the slug's path, so that it will help to impart some accuracy.
Some barrels are 'back bored' (more than a factory tube) and as such, are like a lonnnnnnnnng funnel, going down to the choke.
There is a forcing cone, just ahead of the chamber, anyway, and 'back boring' extends that forcing cone, farther down the tube. (That is an exxageration, but, I hope you get the idea.)
I've shot and I've seen others' groups fired with rifled slugs, that are nothing less than very impressive.
I'm not sure about Mossberg, but, Remington markets/sells a 'fully rifled choketube' that will spin those sabot slugs.
Again, be forewarned, that (depending on which slug you're using), you'll have a real cleaning chore after your shooting session.
Rifled slugs are typically very soft slugs.
G21 Gen2; G19 Gen3; G30SF; G23 Gen3; G26 Gen4. GLOCK Certified Armorer
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Last edited by byf43; 03-01-2010 at 10:08..