Yahoo, Microsoft and Google do not allow gun blog advertising
Microsoft Ad Center does not allow advertising that promotes firearms:
Advertising that promotes firearms or weapons of any kind is not allowed.
Neither does yahoo:
We will not show results on pages that contain problematic content, including but not limited to:
….
Weaponry, ammunition, fireworks or explosives
Nor does google:
Sales or promotion of weapons or ammunition (e.g., firearms, fighting knives, stun guns)
Google’s restriction is only restricted to sales but this has not stopped them from banning gun bloggers.
Unfortunately gun bloggers are out of luck with Microsoft, Yahoo and Google: the mainstream advertising network.

PSclicks.com is actually an online ad agency much like Google that promotes firearms and everything related. We are fairly new and have expanded our network to include over 50 firearm related sites in the first 3 months.
Feel free to spread the word and go to our website to join our network as either a publisher or advertiser.
I guess you are right.
“Google’s restriction is only restricted to sales”
Actually, it appears to be restricted to sales and promotion. Since most gun bloggers could easily be classified as “promoting” firearms, they unfortunately fit.