I have a couple of 20 gauges too.
Near the bottom of the page it says:
Huntsman™ Muzzleloader Barrels
Part # Description Price
50M 50 Cal., 26" (1 in 28" twist) $85.00
50MS 50 Cal., 24" Stainless Steel (1 in 28" twist) $113.00
(Includes Williams fire sights, ramrod, forearm, breech plug wrench and five primer carriers.)
M03451 50 Cal. 26" Stainless Steel (1 in 28" twist) $113.00
(Includes Williams fire sights, ramrod, forearm, breech plug wrench and five primer carriers.)
M03059 10 Pk. of Primer Carriers $15.25
Then it says to "click for an order form".