I have a Mossberg 500 that I want to make into a short defense rifle. So what do I need to know before doing this? Any laws I need to know about?

I believe the min barrel length is 18" so I was gonna do 18.5". So where exactly do u start the measurement?

What kind of choke would it be equivalent to?

Any other tips or pointers I should know?

FYI, I have a master machinist friend who will let me use his shop. With his supervision I was going to cut it on his lathe. But neither of us are gunsmiths. So don't worry it's not me in my garage with a hacksaw.

I chopped one of with a pipe cutter once
Cleaned out the burrs worked great
I'm wanting to cut my win1400 down to 19in

I cut down my 870 barrel. I cut the rib with the horizontal band saw, then cut the barrel in the lathe. Once you cut through the barrel it will have sharp edges inside and out. Bevel the edges slightly by changing the angle of the tool. I measured from the action to 18 1/2".

Sawz-all

Close the action and insert a dowel rod down the barrel until it stops. Mark the end of the barrel on the dowel rod. Remove the dowel rod and mark off 18.5" from the end that was inserted into the shotgun. Now you should have 2 marks on the dowel rod. The measurement between them is the amount you cut from the barrel.

This is how the ATF measures the length of the barrel. They drop an 18" dowel down the barrel on a closed action. If that dowel sticks out of the barrel, the barrel is too short.

I did a few years back for entry guns when I worked B&E or Burglary calls alone. SBS and single bbls. You can adversely affect your patterns and you end with a chamber bore choke ( none ) . Remember to rebevel your bbl and crown it slightly.

As long as the cut is square to the bore you'll be fine. You will have cylinder bore (aka no choke), and as others mentioned make sure to deburr the muzzle. It isn't rocket surgery, just measure twice and cut once. I used a chop saw and mine came out great.

Cool. Thanks for the info folks. Since I've never chopped a barrel, then I wanted to see if there was something I didn't know. Will be finitely deburr and try to cut it off as square as possible.

As for the spread, I'm guessing I won't really know until I pattern it then. After doing so, what are my options if I feels it's too tight? Can I take a counter sink tool and flare it out a bit?
Ultimately I don't want to this to have chokes.

It won't be too tight. You're wanting a room clearing shotgun I presume? I'm sure it will satisfy you as much as it has everyone else that has cut one down before you.

Cool.
I have no idea what to even expect. The only experience I have with patterning and shooting shotguns have all been hunting/clays of some sort.
And unequivocally yes I am looking for a room clearing tool.

If nothing else, you could buy a shorter barrel and a cylinder bore choke for it. Then you could always swap the barrel back to hunt with the gun. But I'm guessing it's not an important shotgun and you want a low cost solution.

Cut one down to 18.25, great for a snake gun

fwiw, i'd make it at least 19".
there are some l.e.'s that measure
differently and you can't argue with them.
last one i did was 20" for that reason.
20 inches is still 20 no matter where
you measure from.
also keep in mind that if you want
to re-install a bead you'll likely
need a taller one.

There is only one way to measure the barrel length, and that is per the procedure as outlined in the 1934 National Firearms Act.

NFA handbook chapter 2

Awesome. Thanks for all the info. I know it sounds cheesy by knowledge is lower and I love it when it's very explicit.
Btw, I have a few other shotguns so I have no need for one gun to serve as both defense and hunting. Also this is another one of those budget builds I like to do. I think I'm going to paint the stock black and modify foregrip and mount a light. Keep it simple and cheap.

yeah, i know how myself, but i'd be nice if
every police officer and deputy sheriff and
game warden in texas knew that. not all of them do.

I don't think we should operate or live our lives based on the possible ignorance of others. That could know no bounds.

Well, whatever it is that you compromise by chopping your shotgun to 20" instead of 18" is probably worth avoiding an ignorant ride in a squad car and trying to get your shotgun out of ignorant impound. YMMV.

Korean Redneck: A cylinder bore is a cylinder bore. The pattern will expand about 1" for every yard it travels.

I guess that old adage "ignorance of the law is no excuse" only applies to commoners? Perfect

I just went out and bought an 18.5" barrel for my 500. Much easier.

I used a pipe cutter and took my time and it worked great.