Ok, at least I'm not totally nutz then, I was beginning to wonder for a minute there!
I went with gut feel & tried some 18.5 Gr loads & visually they seem to be about 85~95% capacity with the bullet seated to the cannelure to crimp. The load was pretty sooty so I'm guessing low(ish) pressure. I went up to 19.0 Gr & the dirt cleaned up quite a lot so I loaded a small batch to chronograph. Any more volume & I think you're going to HAVE to compress a ball powder, something I'm just not comfortable with.
On the bright side extraction is now slick & smooth, & that was the goal when this project started out, a load that would drive a Hornady 125 Gr XTP HP fast enough & have easy extraction/ejection.
I have some once-fired Federal nickle-plated brass & some Starline that is unfired. Give me a couple of days & I'll do a water volume test & post the results. I'll also do a case full of H-110 & Unique for weight & volume as well.
Allan Quatermain: “Automatic rifles. Who in God's name has automatic rifles”?
Elderly Hunter: “That's dashed unsporting. Probably Belgium.”