You can put your own in and just pick them up when you are done.
300 is difficult with .22 LR.
One thing I found is that I can't skimp on the ammo.
At 50 yards, out of my Bergara or my CZ, CCI standard velocity makes pretty much 1 hole. At 100 yards it's 2 inches. At 200 yards it's 8 inches.
Eley Match (at about $16/box) is only marginally tighter at 50 yards, but at 100 is about an inch and at 200 yards is about 3 inches.
For years I thought my Kidd 1022 fell apart between 100 and 200. Then I tried good ammo and found its as good as my bolt guns. ha.