Dand,
The Beeman C1 is a Theoben which is Beeman branded. It is a nice light weight carbine that puts out about 850 fpe. It is a solid well made rifle that is quite accurate and powerful. Of all my rifles, it is in my top three and is one that I always grab when heading out on important hunts.
Regarding caliber and hunting; I hunt a lot with airguns and have for many years. I have hunted in South Africa, Australia, Europe, and all over the States for varied quarry, with a variety of air rifles. I have springers, pcps, and CO2 powered airguns in .177, .20, .25, and 9mm calibers.
Here's my opinion for what its worth; most magnum air rifles that generate over 14 fpe and are accurate - very accurate - can be used for hunting most small game. I have hit jackrabbits, prairie dogs, and squirrels out to 50 yards with a .177 head shot that have dropped them dead on the spot. It is better to have a .177 that you can fire tight groups with than a .25 you can't hit consistently with.
You need to run different pellets through your gun to see what it digests best. I like heavy round nose pellets better than hollowpoints or wadcutters, they are heavy, hard hitting, penetrate well, yet still expands to open a good sized wound channel.
Now I say this within the context of small game, if you are going after marmots, nutria, or larger animals, a larger caliber is better. Practice with your gun, and know what you and it are capable of then bring it into the field and hunt it! Good luck and have fun.
