Can a Primitive weapon Jam? I can see a Black Powder gun jamming, but what about a Bow and Arrow or sling shot?

The only way they could jam is if they broke.

I'd either say that a "jam" just counts as a miss or you fumbled somehow (broke the arrow, lost grip of one strap of the sling etc) and need to take the usual "unjamming" action to ready your weapon again.

A crossbow's mechanism could certainly jam.

With a bow I might go as far as saying the bow string broke although that might be a bit much. Perhaps just fumbling the arrow would be better.

I'd say for a bow, maybe the string fell off or something to those effects? Hmm. Everything else, like Bolas and such, a simple fumble would suffice, and a failure to "un-jam" it shows continual fumbling.

Longbow needs restringing, broken arrow needs replacing, quarrel's head has snapped off, crossbow trigger needs loosening, bolas needs retying or unravelling (although I'm not sure if thrown weapons can jam), blackpowder weapons need cleaning out or need to have their fuse replaced...