I have pressure tested S&B ammo in this caliber, and it is definitely on the hot side. I measured about 58 KPSI peak. I'm not comfortable with that pressure level in Mosins.
You might also take a look at Mojo sights. My eyes are 63, and I have a hard time seeing the rear sight anymore. The Mojos are very simple to install, and they help me a lot.
www.mojosights.com.
Some Mosins have chambers that are slightly too long or too large. They will routinely split steel cased ammo, but brass normally has enough stretch. For those, I shoot only brass cased ammo, and then neck size.
My suggestion is to stick with bullets made for the .303. A bullet .002" undersize will often lead to excessive throat erosion.
Sounds like you're doing it all just right... hope you have a great time, and a successful hunt.