I've got a 20ga Moss500 slug barrel that I would like 2-4" cut off. My local smith was skeptical (I've never used them, just stop by to check the used rack), but I didn't think it could be that hard.

Any smith recommendations for this project?

Or, if there is a simple/cheap tool that I could buy for a DIY, I am all ears.

Thanks!

I will be run clear off the fire for this, to hell with it...hacksaw, small accurate square, mill file, magic marker and fine emery paper. An old paperback copy of the NRA gunsmithing guide if you're the nervous type.

Well... that’s what I’m hoping for! I picked up the whole gun for $120! So I like what you’re thinking.

take it to a machine shop and let them part it off

Been to a machine shop lately? They'll soak the poor guy a hundred bucks just to chuck it up. I have a machine shop, normally I'd cut it off with the hacksaw and true it in the lathe, if it didn't have a vent rib. If you just cut it off, color it with the marker or prussian blue, find your high spots with the square, gingerly and squarely file down the bright spots where the square takes off the dye...you'd be amazed at the neat job you can do. Gently remove the inner burr with the emery and done. I just did a 20ga double for a kid last week, all he wanted was the chokes gone. (Then I took it outside, fired a ladder test at 500 yards with #7 1/2 Creedmoor hi base loads...dead nuts, grin)

Nothing wrong with that. I did that to a 30/06 and it shoots fine. Even cold blued the new square crown.

That's a really simple barrel to true up in a lathe. Moving the front sight back is the harder part (not difficult, just more skill required); it's best to do that BEFORE you cut the barrel though, so the smith can use the existing front sight to mark the new position. If you cut off the barrel first, it'll be harder to locate the exact position for the sight.

If there is no front sight, it's a really simple 5 minute job at the most with a lathe, and a careful guy can do an OK job of it with a hacksaw and file if he doesn't care as much how it looks.

Just don't cut it shorter than 18", as you probably know.

Makes me sad what the American Rifleman magazine has become in my lifetime. Every month there was a home gunsmithing tutorial with common tools, a featured firearm disassembly and assembly, practical stuff for a person on a limited budget. Now? Plug and play, out of the box, turn key, ready to go, plastic and stainless. I'll be a croaker in a few years, but it would be interesting to see what a polymer gun looks like, or a carbon fiber barrel, when they are 150 years old like some of my still functional and accurate rifles from the 1860's.

^^^^^ this and
Watch some goggled up vids
Masking tape
Small jewelers files to shape outer shoulder slightly
Big brass bolt, valve lapping compound
Variable speed cord drill to inside chamfer/ crown
Check for snags with cotton balls.
Lightly and finely emery cloth those.

Fugg paying a gunsmith for a job you can do yourself
Amout you pay him is almost the cost of a brand new 500 slug barrel more than likely.

Just make sure you don’t cut it too short - stay legal...

Also - you’ll need to put a new front sight on which will require drill. / tap and site.. Brownells has kits for this, remember you’ll cut the barrel on a post if it has a vent rib so how you square that off something to think about.

I will admit to cutting a Moss-500 rifled slug barrel with a pipe cutter years ago.

I beveled the outer edge with a file. I don't recall if I did anything to the "crown".

I will make no accuracy claims for this method however, it was more accurate before. But it also had a 3x10x44 scope on it. After the chop it had a 1.5 or 2x. So the drop off in accuracy could have been attributed to the scope or the chop, I don't know.

Were I doing it again today I'd come up with a way to recrown it. I've used plenty of DIY methods, I'd just scale it up.

Crowning won't make it any more accurate. The crowning is there to protect the bore/rifling from external damage. As long as the cut is square and even then that's all that matters for accuracy - consider it a square crown.

May have missed it, but did not see where anybody asked if you planned on mounting a scope. If so, the barrel sights are pretty much irrelevant. Just hacksaw it off, then square up the muzzle with a file.

Never was one to use the little bead anyway.

I did this with a black powder rifle to make it carbine length.

Sawed with hacksaw,then checked with square,then filed and checked some more.

I did the front dovetail with several files and time.

Darn thing shot like it was made like that.