Gerry,
The Remington Model 4 and 6 you are familar with, are the early Rolling Blocks.
Actually a Falling Block for the #6. To the best of my knowledge these were only available in rimfire. However, Remington produced 2 centerfire rifles
from 1981-1987. The semi-auto was a "Model Four" and a "Model Six" in pump action.
This is what you probably saw under centerfire, on the Remington site
ChuckD