The shotgun featured in this post is a beat up Mossberg 500 I purchased for $120. It came with a 30″ barrel and a fixed full choke. I’ll be converting it over to a home defense type gun. First step is to cut and crown the barrel to 18.5″ and install interchangeable choke tubes. Additionally, a new bead sight needs to be installed to replace the one that is cut off.
For this project, Brownells provided the following:
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Screw in choke tubes offer a great deal of flexibility. Since I have Rem Choke tooling, I decided to install a Rem Choke system on my Mossberg (I’m going to give this poor gun an identity crisis).
Prior to installing a choke system, the barrel wall thickness needs to be evaluated to make sure it is thick enough. This is critical in the case of the Mossberg 500 since the barrels are made thinner than those of Remington 870. The Rem Choke tap is .814″-32 TPI. The barrel is .858″ in diameter. .858″-.814″=.044″. .044″/2= .022″. So assuming the bore is centered in the barrel (which it may or may not be) the barrel wall should be .022″ thick after installation.
The high-speed steel reamer used here will not cut a chrome lined barrel (which isn’t a problem with a Mossberg). If you think a barrel is chrome lined, see if it takes cold blue. If it does, it isn’t lined. If it doesn’t it most likely is and you’ll need to remove the chrome lining prior to machining.
A quick note on the order of operations shown here. While I started with the screw in choke tube installation and then installed the bead, I would suggest reversing these steps. The thin wall of the barrel after you machine it can be easily deformed.