The new Perroz Designs 2 Round Shotgun Card is a great concept. Unlike most shotgun cards and side saddles, it is designed to mount on the ejection port side of the shotgun in order to facilitate an emergency reload. This is an advantageous location for the way that most people execute emergency reloads with a shotgun.
The Perroz Designs 2 Round Shotgun Card is secured to the shotgun via adhesive Velcro. I have been using shotgun cards for years and there is no issue with the Velcro loosening under recoil. You may have to replace the adhesive part from time to time if the adhesive starts to break down, but the “industrial” application adhesive Velcro is surprisingly resilient in my experience.
Additional cards can be carried on your chest rig, plate carrier, or anywhere else that has loop side Velcro available.
Check out the Perroz Designs 2 Round Shotgun Card.