We recently tested three short shotshell-chambered firearms. Top is the new Mossberg 590S Shockwave, which is said to handle 1¾- to 3-inch shotshells interchangeably. Center is a Remington TAC-14 pumpgun, which lacks either the factory capability or aftermarket parts to handle mini shells properly. Bottom is a 590 Shockwave, which we originally tested in 2017 with an OpSol Clip that allowed it to feed and fire mini shells. The problem with the aftermarket parts is they restrict the shotshell firearms to only mini shells. There is little difference between the two bottom shotguns. The Remington is smoother in operation, while the Mossberg 590 Shockwave has a superior safety location and holds one more shell. Also, the Remington features an integral fore end stop to prevent the hand from moving forward. The Mossbergs both use fore end loops.
The big question is how did Mossberg modify the 590 to feed mini shells successfully in the 590S? It isn’t that difficult because Mason offers a magazine port insert to cure feeding issues.