Just got in from shooting some 200 gr MKs pushed by RL-26. Below is a copy & paste of sending a report to a new friend I did a trade with on the MO trading thread. I traded LRPs & powder for SPM primers & a LOT of 200 gr MKs. The SD & ES opened up as I pushed the load today, but I had single digits with a little lower vel. RL-26 is magic. Pushing 200 grains at almost 3200 fps
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I shot some of those 200 gr MKs today. They shoot great in my 300 WM. As good or probably better than the 190s. These were loaded with RL-26. I definitely found the pressure limits. Nothing bad happened, but I had heavy bolt lift on a few shot and also light ejector marks. I shot 3 groups of 5 @ 74.4 gr, 74.6 gr, & 74.8 gr. The 1st & 3rd groups were just one ragged hole my thumbnail could cover at 100 yds. Speeds on the 74.8 group: 3183 fps, 3160, 3152, 3158, & 3167. The ES opened up toward the higher powder charges.
I have enough RL-26 now. Scored some more. I was planning on using it for both 6.5 PRCs, .300 WM, & possibly the .243. I have enough data to believe the H1000 is more temp stable than the RL-26. I'm also in good shape on H1000. I'm going back to H1000 on the 300 WM. I mainly just wanted to let you know the bullets are working out for me. I haven't used the primers yet, but feel very comfortable using them when I do.
I think the 7977 is going to work well for you. You might give up 1-200 fps in vel, but that 7977 will be as temp stable as anything on the market.
you take care & let me know how the 7977 performs for you.