No problem at all, and I do tend to use M852/M118LR somewhat interchangably, since I was around for both at various times. The M21 was my "issue rifle" for about three years of my army time, and I used the straight NM M14 for several others on various (5th Army, 101st MTU) rifle teams. I finished up my Distinguished Rifleman badge, and President's Hundred quite some time back (with the black rifle), but am still shooting Service Rifle. Hard-headedness is a hallmark of any real Service Rifle shooter. Getting ready for Perry in another couple weeks, and yeah, still shooting Service Rifle.
The RE-15 will work with both the 168 and the 175, but technically, I guess it was never used for the M852. As I recall, ATK had taken over the operation after the M118LR had superseeded both the M118 Special Ball and the 168 grain interim M852. An interesting, if somewhat convoluted history. As far as the powder choice went, yeah, when Remington ran the plant (and owned IMR), they found that IMR4895 powder was the best available for this load. When Olin took over, surprise (!), they found that WC-750 ws vastly superior. And again, when ATK took over, lo and behold, I was shocked (Shocked!) to learn that they'd doscovered that Alliant's (which they own) RE-15 was the best . . . go figure.
Kevin Thomas
Lapua USA