You're much better off using a very slow burning magnum powder with the 300 RUM - you'll get better performance, and the slower burning powders (at full charge) are more forgiving. The only IMR powder I'd use with the 300 RUM is 7838, but better choices would be Reloader 25, Retumbo, or some of the 50 caliber powders (ie., V24N41 or V20N29 or H50BMG). The 300 RUM is designed to run up 65,000 psi; a pressure at which using the slower powders should give you at least ~3300 fps with a 180 gr. bullet.
The best excessive pressure signs are: 1) extraction marks and 2) loose primer pockets (use a hand-priming tool to "feel" the primers into the pocket). A sticky bolt on ejection could be excessive pressure, but also a partially re-sized case. Continued neck-sizing without full case resizing will eventually create sticky cases upon ejection. Remember: keep track of those primer pockets, because at pressure exceeding 65,000 psi they begin to loosen-up quickly (maybe after only a few reloadings).