301 redirect to old domain

Should I do this or not?

[SEOold]

The best way to explain my issue is with the example below.

Site A - Video site
Site B - Video Site

Both Site A and Site B are duplicate sites. Site A is blocked via robots.txt. We are now changing the content of site B to only Music Videos. Is there any harm in 301 redirecting many of the old files that site B had to Site A? From a SE we don't care because site A is blocked, so its only being done so we don't loose the traffic. This will be a one to one 301 redirect.

With over 500 + redirect would this harm site B domain by any chance? Or should I just give the pages a 404 and call it a day? All suggestions welcome.

[g1smd]

If it is the same content, and it has simply moved, then that is exactly what a 301 redirect is actually for.

[SEOold]

thanks.