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You have certainly fed those loads far more H4831 than I would be brave enough to try. If you can use 67 grains of H4831, then something is keeping the pressure down. Off the wall thoughts, but have you checked your powder scale? Tested velocity with a different chronograph? Also how many rounds have been down that barrel? Something does not seem right...
140 Sierra spbt..61 gr H4831.....March.....2950, 2934, 3000 fps
........................63 gr H4831.....March.....2955 fps
........................65 rg H4831.....March.....3043, 3066 fps
........................66 gr H4831.....March.....3075 fps (w/ a pierced primer)
........................67 gr H4831.....March.....3085, 3145 fps
It is worthwhile to note.
The Sierra manual shows 62 gr of H4831 as max load at 3000 fps with a 140 gr bullet.
Hornady says 58.8 gr at 2900 fps is max.
Nosler #4 does not even list H4831 as a suitable powder. Nor does my old Speer #10 from 1979.
When this data was collected, I was plotting charge weight vs velocity curves. The pierced primer and the flattening of the curve above 3000 fps suggests that the loads are well over maximum. The data was presented for informational purposes, not as a load recommendation.
There are far better powders for this application than H4831. But RL25 is not one of them.
