the basic problem that I've got is that I have dogs and pigs, both of which will eat dead rats. So poisons are generally out of the question for my farm. I've also tried a variety of rat traps, from traditional to electronic, and I haven't had much impact on the population. this rifle has been completely effective at removing rats from my barns. I chose a pellet gun to limit the amount of overpenetration, and for cost-effective shooting. Pellets are a penny or so each, and the air for this rifle is $20 for 50 fill-ups, about a penny a shot. at 2 cents a shot, this is pretty cheap.
This is version 3:
The basic rifle is a BSA scorpion SE, with a picatinny scope adapter and a 10x scope. The scope and mounts are basically stock. Clamped on top of the scope is an infrared spotlight that points in the direction of the barrel, and a 3.5" LCD screen that points back to the butt of the gun. On the eyepiece of the scope is a small camera, so the effect is that you look at the screen and what you see is what the scope is seeing. the infrared addition is manufactured by Nitesite, and it's the NiteSite Viper
I can get between 40 and 50 shots out of this rifle before recharging its internal air tank, which takes a minute or two.
To hunt rats I just turn off all the lights in the barns, and then about half an hour later walk out with the rifle and start shooting. the only visible light is the reflection of the screen off of my face, and I can hit a rats head at 150', so the rats really don't know what's going on, where the shot is coming from, or where to run. So I'll walk out, find a few rats, and start shooting. the first shot kills one rat, and the others freeze for a second or two, trying to figure out where it came from. the next two or three shots kill a couple more, and then there's usually a mass exit. So I go away for a half hour, and come back to the same spot, and I can usually get another rat or two.
I don't know how many rats I've killed over the last 6 months; at least 2500, maybe as many as 3500. I have fired 4500 pellets through this gun, just looking at my ammunition purchases. I thought I had a rat problem, but it wasn't until I had the night vision equipment that I realized how many rats there were in the old barns and sheds. the first night with this rifle I killed 175 rats.
On a typical walkaround these days I'll shoot between 4 and 6 rats as I make my rounds checking the animals, and while that seems like a lot, given the population that I started with, I consider this a manageable level of pests.
the rats are particularly easy to target - their eyes glow in the infrared spotlight, so you can see them clearly from quite a distance away.
Video of nightsite scopes in action (but does have a lot of annoying talk before the shooting)
This video is pretty close to what it's like to hunt the rats on my farm.