In the wars of the Ming-Qing transition period the Manchus mostly attacked in typical steppe style with horseback archers, and the Ming army took the field with edged weapons, early muskets, and primitive pole-mounted firearms. During the battle of Sarhu in April 1619 the Ming firearms, possibly due to problems with the mixture of gunpowder, performed so poorly that some of the bullets bounced off the armor of the Manchu invaders. This lead the Manchus to believe they were rendered invincible by heaven's will. It was to become a decisive victory for the Manchus.
The battle of Sarhu, with on the left Nurhaci's Manchu troops and on the right the Ming army.
The iconic weapon of the late Ming was the sanyanchong (三眼銃) or "three eyed cannon": As the name implies, it consisted of three barrels on a socket that could be mounted on a pole. Examples with more or less barrels are also known to exist. Read more about these weapons on the Great Ming Military blog.
Records suggest some units of the Qing dynasty Green Standard Army still stored weapons called sanyanqiang (三眼鎗) or "three eyed gun", into as late as the Jiaqing reign. I could not find any records of their actual use in the field during the Qing. Also, I could not find records of the Qing manufacturing them, which seems to indicate that they still stored some of the old Ming arms but did not continue the practice of manufacturing them.
Edit: A collector recently brought to my attention that they were used up until to warlord period of the 1916–1928 and by this time, apparently some had been manufacturen with percussion caps, giving rise to the idea that non-regulation production went on longer.
Some survived because they were used by farmers for scaring birds, or for fireworks during new year festivities.
Overall length: 30.5 cm
Barrel length: 11 cm
Bore: 13 mm
Weight: 1588 grams
A classic example, with three barrels wrapped with an iron sheet, mounted on a socket that would fit a pole. Each barrel has its own touch-hole that lit the charge, so one could fire in rapid succession by turning the cannon a third after each shot. Once empty, the heavy head could serve as a mace. Sometimes, the rear of the pole would hold a spearhead for use once the cannon was discharged. It most likely dates from the late Ming but we cannot rule out that some were still produced under the Qing, perhaps in civilian circles.
An iconic weapon of the Ming dynasty, rarely seen on antique markets outside of China.