help with number 4 rollingblock problem

[floridashooter]

I inherited a Remington Model 4 rollingblock rifle in 32 rimfire. It has removeable octigan barrel. The rolling block will not stay up once the hammer is cocked. I replaced the rollingblock, extractor, and trigger spring. Still have the same problem. Any ideas. Does any one know manufacture date. Serial number is J 250000