Stones do not make good projectiles. While the tough structure of jade would make it better than most, rocks generally are just too light compared to lead, and so the range is far too short. Also, a rock that actually fractures inside the bore of a gun can create a blockage that will create dangerously high pressures and at least damage the gun, if not the shooter as well.

Both the French and English fur traders were supplying the northern tribes with trade fusils ( light muskets) by the 1670's, but they'd been used even before this. The Mohawks would use Dutch muskets against the Delawares in 1614, and the Iroquois had gotten at least 400 matchlocks from the Dutch and English traders by 1634 and used them to greatly expand their territory. Quite early on in the 17th c. there are colonist's reports of North American Indians having obtained tools from traders to even make screws, so there really is no question that they were able to understand melting and casting lead, and they would have wanted to, really. Calibers varied from gun to gun, and anyone who got a gun would typically get a bullet mold to match it, and any fired balls that could be reclaimed could then be re-cast. In 1663 the Maryland Colony Council repaid the concession of a lot of Susquehanna land with two barrels of gunpowder, 200 pounds of lead, and a small canon, and there are other recorded transactions where tribes were paid with lead, among other goods.

Brown: Firearms in Colonial America