The value of any firearm is based on the exact make, model, and condition. We need all 3- and you gave us none of the 3. Not possible to even guess. Sorry.
You will need a professional appraisal
50-500 USD depending on specifics
Military rifle made in Spain
Nobody. The M16 is not a sniper rifle, and it did not enter production until 1960.
No such rifle made by Winchester.
made between 1913-1916
Your Mountain Stalker .50 Rifle was made in Spain for Connecticut Valley Arms. These are lightweight, synthetic stocked traditional muzzle loaders. They sold at dept stores for about $115.
Astra is a Spanish company which made a Model 1916 pistol, although they may not have been the only ones.
Your Marlin model 29 slide action .22cal rifle which was made from 1913-1916 will bring between 150-300 dollars for a rifle showing between 50%-90% of its original finish and a decent bore.
It all depends on who made the rifle and what condition it's in..
Sorry, no information means no answer.
You have told us you have a black powder gun made in Spain, but nothing else. Most of these were low to moderate cost modern firearms. Depending on whether it is a rifle or pistol, a kit gun or factory finished, value could be $40-$150.