I have found reliable load data here:
'Steve' has data there for H1000 but not for Retumbo with your particular combination. That doesn't mean it can't be done, just that he hasn't done it.
Not sure why H1000 wouldn't work with this particular combination.
As an FYI, H1000 has a slightly faster burn rate than Retumbo. If a powder is too slow, it will not produce good velocities. Conversely, if a powder is too fast, it will show pressure signs more quickly than others.
You can find a powder burn rate chart here: