You should never use a screw in choked gun without a choke installed it can damage the threads it will cause lead/plastic buildup in the threads and the muzzle is very thin and easily damaged if you happen to hit something with it. Briley will have extra chokes of whatever dimension you want. for Grouse myself I love my 28 ga

It's hard to kill Grouse with the .410 because there is so little shot as compared to the 20 gauge that's why full choke is required to deliver as much shot as possible to the target and you must be a very good shot, unless of course the bird is sitting still. the 410 only has 155 pellets, the 20 gauge 225 in standard game loads with number 6 shot.

Erwin, yes Sir, you can purchase a Modified Choke. This shotgun accepts Win Choke pattern changeable choke tubes. You can find what you need here : nulineguns.com/part_choke_213_3_31_36.php

Erwin, Your gonna have to pattern the shotgun yourself. Of course it will open up if your just shooting cylinder choke. This shotgun will take the Win-Chokes choke tubes in .410 so there are modified choke options out there.