I have some data from a Marlin 375 I once loaded & hunted with.
First in my case H-335 proved to be a very poor powder..poor accuracy & decent velocity but with a lot of muzzle blast.
Check all your loads with a chrony, I found very few published loads actually came anywhere close in velocity claimed.
If you get to actual 2000fps with 220 horns with any accuracy..BE HAPPY
In most cases getting enough powder in the case was the deciding factor to eliminate a powder.
In the end either of the 4198 powders worked very well.
The loads I decided on for hunting was 33 1/2 gns of IMR 4198 @ 1950fps.
Best accuracy was 32gns of same powder.
Another peculularity I found with the Marlin was point of impact??
With 4 diff powders at roughly the same velocity I had points of impact of Left 6", Low 3", Right 5" & back to Left 6"
I chrony'd the two factory Win loadings as well with results of 2220fps for the 200gn loads & 1775fps with the 250s, so you can see the 220 Horns run right in the middle velocity wise.
Hope that helped a little
