Under certain ammo there are specs like -10 Dt or x3 weapon condition. Most of them I understand but for the ammo that has x? weapon condition does that mean it speeds up weapon degrading or lessen it?

Speeds up. Those are the "bulk" cheap ammo. They gum up your weapon worse than regular ammo.

I see. Thanks for the clear up.

Are incinderary ammos affected by the Pyromaniac perk? I'm most interested in indinderary grenade ammo.