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Browning's web site has the current information.
Yes
No, Invector chokes will not fit the Browning Medalist shotgun. The Medalist typically uses fixed chokes that are integral to the barrel, while Invector chokes are designed for Browning shotguns with removable choke systems. It's important to check the specific model and choke compatibility for your shotgun.
The markings on the receiver and barrel will tell.
Library.
No. Not recommended. The barrel walls are not fit for screw in chokes. Belgian A-5 barrels that had that procedure done in the 60's and 70's were mostly unsuccesful. The barrels ended up being cut down or discarded. Aftermarket screw in chokes worked well with the Over/Under Browning guns, but not the Automatics. It's recommended to purchase a Japanese made barrel (with invector chokes) and have it fitted to your Belgian gun.
50-500 uSD
There is no "Standard" choke. A5's could be purchased with one of many different chokes, however, the more common chokes on a 28" barrel were Full and Modified
$150 - $400 depending on condition and year made (barrel markings determine the period when the barrel was made)
Browning Choke Markings "* " = full "*- " = improved modified "** " = modified "**-" = improved cylinder "**$" = skeet "***" = cylinder
You will need to contact Browning.
BROWNING CHOKES AND THEIR CODES (ON REAR LEFT-SIDE OF BARREL)* designates full choke (F).*- designates improved modified choke (IM).** designates modified choke (M).**- designates improved cylinder choke (IC).**$ designates skeet (SK).*** designates cylinder bore (CYL).INV. designates barrel is threaded for Browning Invector choke tube system.INV. PLUS designates back-bored barrels