Personally I believe that the word of the legislation in Scotland does include paintball and a certificate would be required
There was an exemption for paintball during the drafting of the legislation but that was removed from the enacted legislation.
People have subsequently asked their local police stations and been told that they dont include paintball (that the firearms officers don't feel it applies or they don't consider paintball worth enforcing - the aim of the law like the Vcra is to deal with neds (chavs in English))
Decide for yourself whether to clarify with your locals or keep quiet. You will have either no problem at all and can happily store your gear and carry it packed or you get caught with it and rely on the circumstances of if it it pursued or not.
(Note that frangible falls under other firearms legislation and is a measure of lethality, all the legislation together is a minefield, and as such a paintball gun before the new Scottish legislation was defined as an air weapon that fired frangible projectiles).
http://p8ntballer-forums.com/threads/paintball-and-the-law.171875/page-6