I don't know a lot about the Marauder .25 and how much energy it puts out, but if it's more than the .22 version, or over 30fpe at the muzzle, then it should do the job just fine, but only with a well placed shot in the head and not from very far away.
I would try and get within 30yds with the Marauder. The goal is to quickly and humanely kill it on the spot, and post the pics here afterwards.. like immediately
But seriously speaking, this means getting close to ensure an accurate shot to the head but where it counts on the head, not its jaw, nose, or somewhere on the neck. It has to be its brain.
If you can get your hands on a powerful PCP like a Condor (.22 or .25), even better. You could take the beaver from 40-50yds easily but again, it has to be a very good head shot so it goes down fast and you don't just injure it and lose it. We had a kid here about 2-3yrs back (or was it on the Dianawerk forum?) that took a 35lb beaver with his 350 .177. A single shot to the head from 20 or 30yds I believe, and he said it dropped dead in its tracks.
Beavers actually get pretty large but many Coyotes (and plenty of fox) have been taken with mid powered PCP's and Magnum Springers. A beaver's head is probably slightly harder or thicker than a Coyote's, but it is just bone, not steel or pressure-treated wood. We are not talking about a bear or a wild boar here. Even if the beaver's head is equivelant to say wood.. that's no problem. My Condor almost goes through a pressure-treated 2x4" (or 2x8") from 25yds out. You can see the splinters sticking out in the back or part of the pellet. At 10yds Kodiaks go right through it as long as they go >1,040fps. I think the challenge here with the Beaver would be to get up close within normal "airgun ranges" (25 to 35yds), especially because it is a large one with a good size head. It would not be much of a challenge taking a shot at it with a 30-06 from 75 or 100yds out. A .17HMR or .22 WMR maybe, not not a centerfire gun.
If I had to use a powder burner, I would just use my .22LR (~125fpe) which is deadly accurate at 50yds.
You are only going to need about 15fpe on impact (to the head) to drop this beaver so an airgun will do. 15fpe is the same to shooting the beaver with a Diana 34 .177 or .22 at point-blank range. Do some of you think you cannot kill a beaver with a shot like that (900fps w/.177 pellet or 680-700fps in .22) betwen the eyes from 1" away? I know people (through other forums) that have killed feral dogs bigger than a beaver with the same or less "firepower" from 15yds out. It's all about shot placement. Forget the powder burners. You can take the beaver with your Marauder if you are patient enough and practice a lot until you can place that pellet inside a nickel-sized hole every time (at 30yds and beyond). Should not be too hard to do with a PCP like the Marauder. Good luck and let us know the outcome.
