I gave up on the old fashioned side hammer guns because I could never get mine to fire after being in the field in damp weather. I snapped 4 caps on a deer one time and missed because of I flinched during the hang fire on the 4th cap. Funny thing was, the deer stood their looking at me the whole time and finally ran after the gun fired.
I now use a Knight Revolution and can leave it loaded all season and it will fire like I just loaded it. I use pellets and the Knight has the primer in the jacket which forms a water tight seal. I do not store the gun with the primer though. The video that came with the gun has a guy load it up, walk out into a pond and fully submerge himself and the gun. He comes out, drains the water out of the barrel and fires it without a problem.
So far, I have had no problem with a modern inline rifle and hope I never do.