Howdy... and welcome!

Any brass marked R-P 30-40 Krag is modern Remington brass and safe for reloading.  I have reloaded some of my Remington brass well into double digits and it's still going!  Yes, I do get neck splits occasionally, but you can extend this greatly by annealing the case necks.  It's a very simple process of heating the necks until they change color down the shoulder (but NOT glow), and then allow them to cool.  Do it every few loadings, and it will pay dividends in saved brass.

Also, neck size only to save on wear of the case.  Keep the brass with the gun (in other words, don't neck size and then fire in a different Krag, as the brass is fire-formed to the chamber). 

If you want new brass, Graf & Sons now sells 30-40 brass with a GRAF headstamp on their site.

Just go easy... keep the pressures light, and your brass will serve you well for a while!