The M16-4 was introduced in 1989 with guns being made
in 4", 6", and 8 3/8" barrels. The 4" and 8 3/8" barrels were
discontinued in 1992, with the model 16 discontinued in 1993.
Just guessing I would say the 8 3/8" barrel was the most
rare and the 6" most popular. Just a guess !!! Don