In '65 I had a M-14, but I went back in '66-'67 (2nd Bn/3rd Inf, 199th Light Infantry Brigade) and had a original M-16. We did not use LBE (Load Bearing Equipment or Web Gear) for ammo pouches, all pouches at that time were for M-14 mags, you could put three M-16 mags in one, but it was kind of screwball as I recall.
M-16 ammo at the time came in regular metal ammo can with three bandoliers of seven twenty round boxes ( packaged as two ten round stripper clips) per bandolier. Usually there were two magazine loader adapters in each can. You placed the adapter on the empty magazine,, inserted a stripper clip, pushed the ammo into the mag, tossed the empty clip, put a second one in the adapter and down they go, remove the adapter, download two rounds to eighteen. that was Company SOP for a clean dry magazine.
The eighteen round download was so you could easily reload your rifle with a closed bolt, better than the magazine falling out when you acquired a target.
I used the now empty bandoliers to carry six loaded magazines, the middle bandolier pocket left open to rest better against your side. I carried three bandoliers of ammo and one of six frag grenades, if going on ambush from base camp I had second bandolier of grenades.
On return from whatever or base camp had cots so I sat on the cot and cleaned the rifle, taking it down to the bolt if it had been fired or not as were were in rice paddies and other wetlands. If fired I used solvent to clean then dry patches, finally wet patches of LSA (gun oil) and everything coated in gun oils and wiped down with a towel or Tee Shirt,
Then to the magazines, all nineteen. I took the liner out of my pot and stripped all the ammo into the pot. I then disassembled the magazines took a oily rag and a toothbrush, then a dry rag. Then a visual inspection, I rarely needed my bore brush. Once reassembled I tackled the old ammunition with the premise it may have been dunked, I wiped each round after inspection, with a oily rag and then dry one, re-inspected and then loaded one by one to the top and then down two rounds (Hard to keep count with everyone's activity and all) always interrupted for something. Replace any rounds tossed with new, stuffed the brushed bandoliers and I was ready Freddy.
All we had were twenty round magazines.