Magazine tube extension Rem 870

[FRJ]

I have a 20" barreled Remington 870 and would like to know how long an extension I can put on the existing mag tube without going past the muzzle.
2,3,4 shells. It is a 3" chamber gun by the way. FRJ

 

[Flea]

I have an 870 with a 20" rifle sighted barrel and a factory extension (3" chamber) and it's a 7+1 gun.

My $.02, you're probably looking at a +2 extension.

 

[readyme]

FRJ, email sent to you.

 

[Grunt]

Yup, the factory extensions are +2 for 18.5" barrels and +3 for the 20 inch tubes.