I weighed a bunch of those 173 pulls too, and got exactly that spread. When I shot Service Rifle class High Power with the Garand we used SMK 180s for 600 yards; the 175s weren't out yet. You could try them if the 175s don't work.
Can't read a thread like this without reminding; CMP used to sell all the parts for M1s and had run OUT of operating rods by the time I got into M1s in the early 80s. Stick with the faster burning powders
so the pressure peak occurs early and dissipates before the bullet clears the gas port just behind the front sight. Slow burning powders peak later and a slammed op rod will bend badly.