GMM has been loaded with IMR4064 and Reloader15. The current Navy version of M118LR (Mk316 developed for SOCOM) uses a 41.75 gr charge of IMR4064 with a Fed GMM primer, 175 SMK. Standard M118LR brass.
The 4064 charge is supposedly more temp stable than the Re15 load, according to NSWC Crane.
Machine guns are awesome until you have to carry one.