my advice, is don't tell them what's in the bags.
I was advised this by both British Airways and Air Canada last year. Carrying a paintball marker with a decompressed air tank is not against any airline policies, (unless ryan air have changed their policies in the last few months).
Last year i was actually told off for bringing it to the attention of the check in stewardess, as she had get security on the case, and they had to call their supervisor... basically they just said i was being a pain in the ass, and should not waste their time with something that wasn't a security risk.
That said, always have a copy of PGI tucked in your pack, so they know what it is.
good luck