Tim,

Your R16 story sounds just like mine. Rounds are hard to chamber by pushing with the sliding action, but easy to do by hand.
The action closes normally when there are no rounds being loaded, therefore I think the leverage works properly.
THe shells show signs of friction on the brass and the breech side of the chamber measures less than standard, so I believe I found the problem. I will try to polish a bit the inside of the chambers where they seem to rub the rounds.
Thanks for the advise.