@Kevadu this is actually pretty common, even in the US. Federal law limits ammo capacity to 3 when hunting migratory birds. So it's easier and cheaper to limit your current gun rather than buying a specialized one
Yes, you use a spacer to lower the amount of rounds you can have in the shotgun. This is to abide by hunting laws that deal with limits (how much game you can kill).
EXTRA PAGES LETS GOOOOOOOO
Also know we know why releases are spread out...The authors and parents declining health, father's death and Bun-chan's passing :( Getting older is hard