It wasn't accessible on 30” barrels, deer guns, goal guns or for a retrofit. This patented procedure enables the shooter to utilize a wrench to change the shotgun to entire, modified or enhanced cylinder chokes. Remington also extra the 12-ga. Design 870 SP Specific Reason Deer Gun into the Deer http://pumpaction71470.blogolize.com/5-Simple-Statements-About-remington-gauge-pump-action-shotgun-Explained-51067550