This is the second of these guns that I've owned. This is chambered in 9mm shot rimfire otherwise known as ".350 Glatt". The glatt I believe refers to the bore as being smoothbore. These guns are typically single shot bolt actions, however I have seen some combination guns with a rifle caliber on one side and the smoothbore 9mm on the other. Bernardelli also made an autoloader in 9mm, but I've never seen any pump guns in this chambering. Apparently, they have (and possibly still do) make these this shells with a round ball for short range dispatching of garden pests. I prefer to use the shotshells and have found them to be quite effective on small varmints and birds. Shells can be found in size 6, 7.5, 8 and 9 shot and typically are purchased in packs of 50. Traveling at roughly 600 fps and containing about a quarter ounce of lead shot, you would be amazed how they can shed a feather on starlings. I finally decided to take this Simson made prewar gun to the pattern board and see how it printed. Shot at 15yds and 25 yds. The picture with the circled hits is at 25 yds. Enjoy the pictures...