Check out MidwayUSA. I use a Choate. Current price ranges from 43 to 46 dollars. from +2 to +5. A plus 3 for a 20 inch barrel. Personally I have not seen a 20 inch barrel, only 18 1/2, 24 and 28 inch. I bought the plus 5 and it was too long for my 24 inch rifled barrel so I cut it down to make it a +4.