apparently you have to book them in as sports equipment (seperate option when booking flight) costs 50quid but i think its like 50kilo weight limit and any size, so no need for other luggage, use the bottom half of the navigator for party clothes and the rest for balling gear
It cost me 8 quid calling Ryan Air to find out about tanks and markers! (premium rate line). So hopefully I can save some people the trouble of calling them.
Basically, the unhelpful woman at the other end of the line said that "so long as there are no pressurized items [in your 'sports bag'], you shouldn't have a problem" with regards to air bottles. I also checked out markers with her and she didn't really know the answer to that one, but said that so long as it's not a firearm (which according to the UKPSF it's not) it'll be kosher.
I think Dave is right in saying that the best way about this if you're flying Ryan Air will be to Check in at the airport, but with no luggage and sacrifice the £50 so that you can take a sports bag and get the extra weight.
Dave also suggested including a paintball magazine in the bag so that anyone who may open it will hopefully realize that it's a non-lethal sporting good!
Edit. If you haven't booked your flights, book REAL soon, because the price has gone up in the last couple of days.