If your mainspring is not producing enough energy for reliable ignition, put in a new one. I install new Wolff mainsprings.
http://www.gunsprings.com/Rifles%20%...2/mID40/dID176
For a M48 I would use the 22 pound spring, the lightest one they have, the heavier springs make bolt lift hard.
Basically I install new mainsprings on virtually all of my old bolt rifles, it really makes a difference in lock time, on military two stage triggers, it often reduces creep on the final stage.
In so far as 1955 powder, it close to the end of its shelf life, if not beyond, I would not load up hundreds of cases and have the stuff sitting around. I did that with surplus IMR 4895, before I found gunpowder has a shelf life, and within a year, I lost 700 LC Match cases due to cracked case necks. As gunpowder deteriorates it outgasses NOx, one byproduct is nitric acid gas. Gunpowder has stabilizers that consume this NOx, but given enough time, the stabilizers are gone. That nitric acid gas will ruin brass. You will see pin hole though corrosion on old ammunition, that is the nitric acid gas eating up the brass.
Also, if you get sticky extraction or “funny” retorts, stop using it . Old powder will blew up actions.