I have a 7mm Mashburn that was built on a Rem 700 action. Certainly not a lot of load data out there especially with new powders. Did a little looking around and I see the 28 Nosler case is listed as having a case capacity of 93.8 grs of H20. The 300 Win case is listed as having a capacity of 94 grs. now the shoulder is moved back a few thou on the 300 Win case to form the Mashburn case so capacity of the Mashburn may be reduced by a grain or two but still very close. It would make sense to reduce start loads by a grain or two to load the Mashburn but the 28 Nosler data will certainly provide Mashburn shooters some reference material. I am looking forward to trying StaBall HD in my rifle

I have both of those 2 cartridges and would advise you to look up data for the 7 Practical to use for the Mashburn. On average my loads for it are a good 6-10 grains less than I use in the 28 Nosler. It performs better with powders I’ve found too slow for the Mashburn. The Mashburn does very well with H1000, Retumbo and Ramshot Grand. Great cartridge overall, my favorite 7mm chambering.