Finally had a chance to finish chronographing test loads for my Winchester Self Loaders. Below is my range report.
.351 WSL
Load #1 - 15.0 gn H110; 182 gn Buffalo Bullets JRN; Jamison Case; Rem 6 1/2 Primer: Cycled fine; Avg vel 1,378 fps. Velocities were very inconsistent. Some of the cases were sooty. I believe this load was not always sealing the chamber.
Load #2 - Increased to 15.5 gn of H110. Velocities were still inconsistent. Some of the cases were again sooty. I believe this load was not always sealing the chamber.
Load #3 - 15.5 gn 2400; everything else the same: Cycled fine; Avg vel 1,674 fps. SD 17.52; I believe this load, while under factory velocities, is worth keeping.
.401 WSL
Load #1 - 22.0 gn 2400; 200 gn DKT SP; QC Case; Win WLR Primer: Cycled fine; Avg vel 1,770
Load #2 - 23.0 gn 2400; 200 gn DKT SP; QC Case; Win WLR Primer: Cycled fine; Avg vel 1,868
Other notes: Both of these rifles throw the brass far and tend to ding the case mouths. I spend a lot of time looking for brass when they cost $2.00 each. (They were throwing them over the tarp I had laid down.) Factory velocity for the .351 is supposed to be around 1,850 for a 180 gn bullet and for the .401, 2,135 for a 200gn bullet. Since I'm cycling reliably, I'm probably not going to go any higher. These guns are old, and the ejection is vigorous enough.
Here's a picture I shared before