Remington made 20 gauge shotguns on two frame sizes.  Many parts (including barrels) are not interchangeable between the two size frames.  There seems to be much confusion about determining the correct frame size especially when purchasing a slug barrel.  Here is how to tell them apart:

Frames that have a serial number that ends in “K” or “U” are the small frame guns.  They have 20 gauge diameter magazine tubes and barrel rings. These are true 20 gauge size guns. They are lighter and slimmer than the large frame guns.

Frames that have serial numbers that end in “X” or “N” are large frame guns. They have 12 gauge diameter magazine tubes and barrel rings and are built on 12 gauge size receivers.  They require 12 gauge trigger groups and 12 gauge wood.  They are larger and heavier than the small frame gun.


The Remington 870 is a good example of a 20 gauge shotgun

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  1. Brian Weigel at Nov 18, 2011 11:07:31

    hmm lesomething every day!!

  2. Laramie Hawk at Sep 14, 2012 02:56:03

    I have a 20 gauge 870 that is built on the 12 gauge frame serial number ending in “N” I believe. I have been looking for a long time for a slug barrel for this shotgun and have had no luck. Would you know where I could look for this? Please E-mail me if you do know.


    • PaulJacobson at Feb 08, 2013 08:29:06

      Hi Laramie,

      I’m sorry but I don’t have an answer for you, Remington did this same thing back in the 70’s with the 1100 shotgun. I guess all the people involved in that disastrous decision either left or retired, because they repeated it with the 870. Try contacting Remington to see if they have any barrels they are holding out for warranty repairs.

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