If you're not going through Schiphol airport in Amsterdam, you should have no hassle.
Like others have mentioned, take off the barrel and remove batteries. On paintball tanks you must remove the tank regulator so you can see inside the cylinder. Also, I printed out TSA forms regarding their policy on air tanks, attached one to the tank with a rubber band, and kept the other in my carry on. I've only traveled with air tanks pre 9/11, but I doubt there would be any problems since I'm able to still bring markers back and forth between Norway and here.
One last note; have everything paintball related in your checked luggage! I was an idiot one time when I traveled back to Norway. I forgot to pack my 14" Redz barrel in my luggage, so I just threw it in my carry on. The security in Schiphol held me for about half an hour. At first they didn't have a clue of what it was, so I had to explain to 4 different people what it was several times. After they finally got it they had no clue what to do, and just stood idle. After getting nowhere, I just told them to keep it and use it as a gentle pleasuring device (to put it lightly). Not a big deal because it wasn't my favorite barrel, but you guys can laugh at for that one
Also, another time I was going through Schiphol, calling it a marker didn't work. Before I was to board the plane, a clerk called me to the front desk and I was questioned by another man.
Basically went like this;
him: "We believe you have a gun in your luggage"
me: "no, I don't have a gun, but I have a paintball marker"
him: "do you have anything that resembles a trigger in your luggage"
me: "yes, a paintball marker"
him: "is it a gun?"
me: "it's a paintball marker, gun, I don't care what you want to call it, it shoots paint"
him: "YES! it is a gun.... ok you can go"
Wow, just realized I gave my life's story there lol