12 ga muzzle opening

[Kroy]

I have a 870 12 gauge 20" barrel with a muzzle insert choke.
I use this as a camp gun in the mountains, and would like to know what size muzzle diameter do I need to shoot slugs.
I want to be able to load the gun ooo,ooo,slug,slug,slug (5 round magazine).
Presently I load it 000 all the way.
Any suggestions?

 

[Ahsan Ahmed]

When you say "muzzle insert choke" I take it that your barrel is threaded for screw-in chokes (likely Rem Chokes)?

As it is, one could shoot lead slugs through all kinds of constrictions i.e. from Full to Cyl in a smoothbore barrel. However, what choke/slug combo may perfom best is usually dependent on the individual shotgun/particular brand of ammo being used and this would vary from firearm to firearm. More open chokes types such as IC are recommended.

The IC choke generally works well with slugs in most smoothbore shotguns. I would try both IC as well as a Mod choke to determine which works best in your particular shotgun. I would also test that using (various brands) of both slug and buckshot at 35-50 yds.

Hope that helps.

 

[Kroy]

What I need is the diameter of a full choke, improved cylinder and no choke.
I tore apart two shells, one had a slug in a shot cup (Lyman cast) and one was a rifled slug with no cup (round top / hollow base).
The slug/cup looks like it might make it through but the other slug would not.
The insert (make unknown) would definitely not have let the rifled slug through.
The insert has already been bored out once.
Once I know the sizes, I will be able to sort the assorted slugs that I have.

 

[Ahsan Ahmed]

A lead slug would still compress sufficiently to exit even a full choke....what that may do to the accuracy is a different question due to so many variables. Anyway, here is a chart that you could consult....the calculation shown are in inches.

Out of curiosity, what is this insert that you refer to - a choke tube or a fixed choke sleeve that was installed at some point in time? The later seem unlikely though in the case of an 870.

 

[iceman2]

In an unrifled, choke restricked barrel a rifled slug should be used. (hollow base) They are designed to compress and fit through even a full choke. These have been used for decades with no problems. The solid or slugs in sabots are designed for rifled barrels and will not compress through a choke very well if any and could cause a bulged barrel.