The 300RUM is designed for some freebore. Most magazines can only handle 3.65" COL. I went around on a quest once with my trusty stoney point COL and a few bullets. I found the freebore to range from 3.7" to 3.8". In other words one would have to load 3.7" to touch the lands.

I found accurate loads at 3.57" and 3.4". Go out as far as you can. Load up several different COL's and find the most accurate place.

Look at your case and bolt lift to find pressure signs.