I agree about the range issue. In a 'survival' situation, you probably won't be shooting things any further than 100 yards in most cases though, but I still put that too far for a slingshot and most airguns. Blowguns are fun, but compared to a slingshot or a air-rifle, they are impractical in my opinion. Ammo choices are very limited and accuracy is not as high as with a slingshot. A blowgun shoots darts -- a slingshot shoots small objects (much broader category). Compared to an air-rifle, I will give it to the air rifle - you can carry more ammo and don't have to worry about sticking yourself with it. Now, as a ninja weapon, blowguns are awesome and I highly recommend them Haha!225 yard range doesn't mean 225yard accuracy. 22LR ammo has 1.5 mile range on the box. Doesn't mean you can shoot a squirrel in the head at that range. just point it at a 45 degree angle it may go that far.
How about a blowgun? The .62cal models look promising with good power.
I used to have a .40 Jivaro model in my youth and could hit lizards in the head with it at around 30 feet. Slingshots are powerful as well especially when combined with marbles or lead round balls for ammo.