Carlson's Choke Tubes Magazine Extension Assembly Winchester 1200/1300 12 gauge 7-Round Black. These magazine extensions are constructed of blued solid steel and come with spring base clamp with swivel stud (included) to work with quick detachable swivel (not included) and a high visibility follower. The threaded tube replaces you magazine cap and gives you the ability to add extra rounds to you magazine. Easy to follow instructions are included. The magazine extension tube is great for home protection competition shooting and law enforcement. See chart below for the make/model and the magazine capacity. Overall Length of Extensions: 04500 (8.25-inch) 04501 (10.5-inch) 04502 (6.25-inch) 04503 (6.375-inch) 04504 (14.25-inch) 04505 (8.25-inch) 04506 (6.25-inch) 04507 (8.25-inch) 04508 (5-inch) 04510 (13.88) and 04511 (8.5-inch) 04512 (8.38-inch) 04513 (8.13-inch) 04514 (14.13-inch) 04515 (8.13-inch) 04516 (14.13-inch) 04517 (8.5-inch) 04518 (14.25-inch) Magazine round count is for the total capacity using 2 3/4-inch shells including 1 in the chamber when using 3" shells you lose 1 shell capacity. When using 3 1/2" shells you lose 2 shell capacity. Example: 8 shot extension= is 7 (2.75" shells) in the extension and 1 in the chamber 6 (3" shells) in the extension and 1 in the chamber or 5 (3 1/2" shells) in the extension and one in the chamber. Remington extensions require removal of tabs / detent in magazine tube on newer model shotguns All extensions are 12 gauge only. Specifications for Carlson's Choke Tubes Winchester 1200/1300 7-Round Magazine Extension: Manufacturer: Carlson's Choke Tubes Color: Black Finish: Blued Fabric/Material: Steel Magazine Capacity: 7 Round Gun Make: Winchester Gun Model: Winchester Model 1200 Winchester Model 1300 Included Accessories: High Visibility Follower Base Clamp Spring Length: 6.375 in Country of Origin: USA Gauge: 12 Features of Carlson's Choke Tubes Winchester 1200/1300 7-Round Magazine Extension Winchester 1200/1300 Magazine Extension 7 Shot Package Contents: Carlson's Choke Tubes Winchester 1200/1300 7-Round Magazine Extension barrel clamp plus & spring What firearm models does the manufacturer say Carlson's Choke Tubes Winchester 1200/1300 7-Round Magazine Extension is compatible with? The manufacturer suggests that Carlson's Choke Tubes Winchester 1200/1300 7-Round Magazine Extension is compatible with Winchester Model 1300 Winchester Model 1200Carlson's Choke Tubes 04503: Magazine Extension Assembly Winchester 1200/1300 12 gauge 7-Round Black