I was in Vietnam from 5-66 to 5-67 II Corps
I saw every conceivable weapon the Army ever used. There were M14s that most of us had, grease guns, carbines both M1 and 2, and even some Thompson SMGs. M16s were so new and few that only Infantry Battalions were being issued them. Pistols .45 and .32 autos. The Army still carried lots of stuff on the books for issue, I read the book one time and it was neat. Like a gun Sears catalog. The Korean troops and most of the Mike force guys used M1 rifles and BARs typical Korean war stuff. Our Machine guns were .50 M2s and M60s, but there were 1919s around as well. The enemy weapons were very diverse at first as the PAVN troops and their front line weapons were just arriving in force. Typically, if you were shot in spring of 66 it was with a US carbine or a Mauser. Some SKS were around and very few AKs, there was even an in-the-box new MG34 captured complete with saddle mags and tripod for AA use. By fall of 66 and into 67 everything changed as NVA troops started to get involved at places other than hard on the Laos/Cambodia border. AKs became very common and RPD machine guns and the like. Mostly Chinese made. I was thrilled to be in a Signal Battalion and run convoys down HWY 1 instead of looking for trouble up at the Dets up near the border. Those mobile Infantry Battalions had a bad deal in 66 and 67 up in the highlands. When I went up into those bases at Pleiku and An Khe it was very weird knowing that you were in country with a 15 year history of dead men, shot up convoys and bad vibes. HWY 19 ran though this area and west of An Khe the Viet Minh had wiped out a huge French convoy in 1954 up there. We saw lots of jungle junk left over from the French war.