I just reread this entire thread and have the answer I was was looking for in my original question. MS110 is what I'll be installing in my M15. As LUTNIT said, it should produce about 390 in a full length G36, so I should expect about that with my M15 once I get it upgraded. I'll pass on the nozzle and tightbore for this gun because it will most likely bring it above 400 fps.
However, I should be safe to install the tightbore and airseal nozzle on my C8 and keep it below 400.
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