From various figures given about muzzle velocities with SMK175 in the .284Win, I get the impression that 2850fps is about as high as you would go with pressure and its consequences being the limiting factor. You could probably say an equivalent MV for the 142SMK in a 6.5x284 is 3000fps. Now I'm sure some people will talk about 2950 with the 284 and I can come back with 3100 with my 6.5x284. But neither of us would load to that normally.
So, using those figures, and the highly respected figures from the Sierra website, I calculated the following drift figures at 1000 yds (for a 20mph cross-wind) :
175grSMK in 284Win at 2850fps : 137.9 inches
142grSMK in 6.5x284 at 3000fps : 136.4 inches
So, in practice, the considerably higher BC of the 7mm bullet does not give less drift at the ranges we normally shoot, because in practice, it starts off about 150fps slower (and at 1000 yds it is still slower - I get 1527fps vs 1570fps for the 6.5).
It might be interesting to see how some of the quicker 6mm cartridges compare.
Alan.
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