in my 44-1/2 I use 4g Unique and is a very mild but accurate load. I use the SAECO 325 mainly or a 90g I buy from Desperado Cowboy Bullets.Hes local and his bullets are 20-1,not Hardcast and are very accurate.
I use pistol primers.

FWIW - I've shot quite a bit of 32-20 through a #2 Remington rolling block. A rifle of similar size.   

My favorite load is 12.7gr of Reloader 7 under a classic 311008, 115gr bullet.  Very accurate.

As for 2400, I found 8.2gr shot very well with the same bullet and gave 1175fps.

Both using CCI small pistol primers.

I've found that modern-made 2400 (Alliant, etc.?) is hotter/faster than the old Hercules-made 2400.  I learned that loading .401 WSL cases for my old 1910 Winchester.  That rifle needs a hot load to function and even the factory loads were close to 50,000 psi.  I used the load recommended by Phil Sharpe in his 1937 Complete Guide to Handloading.   

When fired, that load blew back the breechblock so fast that the ejecting case was caught and bent by the returning breechblock.  Flame from burning powder came out of the ejection port.  That adventure taught me a 2400 lesson.

With a Stevens 44 action, I would approach even long-recommended loads with caution.