Depends on how restrictive you want to be regarding the definition. There were late 17th Century examples of man-portable muskets which would fire multiple bullets in succession by using the Roman Candle principle. What we call today automatic weapons just weren’t very practical until the development of metallic cartridges and smokeless powder. John Browning’s conversion of a lever action rifle to muzzle blast actuation was an early example, but I don’t think it was ever fully automatic. There may have been some early adaptations of recoil-operated pistols to full auto fire around the turn of the 20th Century, but I don’t know of any. The Italian Villar-Perosa was an early example of a submachine gun, and I think that was developed around 1914. Another example of a man-portable full auto weapon was the Benet-Mercier automatic rifle which could be carried and fired by one man in much the same way as a BAR could be, but was best operated by a two or three man crew. It dated to around 1908. The Lewis gun is a similar example,as it could be used like a BAR by one man, but was more effective when used by a two or three-man crew.