In reply to the original post, to clarify things here. There's been a lot of this is better than that discussion here without many actual numbers quoted.
I'm going to use Hodgdons load data here, comparing like with like, to save any high pressure handloads being compared with factory velocities etc etc. I know exactly what we get velocity verses pressure measured with the Oehler 43 Ballistic Lab for all these options, but for the sake of transparency we'll go with Hodgdon's latest data off their website. And our data differential pretty much matches Hodgdon's anyway, even if we are loading to higher pressures and velocities.
In the 7mmRM with the 180gn Berger G7BC of .345, Hodgdon list 2920fps for 59,600fps with 71gn of Retumbo.
In the 300WM with the 208gn A-Max they list 2915fps for 61,300psi with 81gns of Retumbo. They don't actually list the 215, but in our experience you will loose about 50fps to 75fps from the 208 to the 215 (the general rule of thumb is 100fps per 100gns of bullet weight for these sized cartridges), so lets choose the lesser velocity loss and say 2865fps. G7BC .356
With the 230gn Berger G7 BC .38 for the Target (the OTM is .368, but we'll assume the higher BC of the Target), they say 2774fps for 61,300psi with 72.6gns of 7828.
If you run these numbers there is very little difference in trajectory and wind drift to 1500 yards between the 180gn and the 215gn. The 180 drops slightly less than the 215, and drifts ever so so slightly more. If you assign the same pressure for both (remember we had 59,600psi for the 7mm verses 61,300psi for the 300), which will have the 180 doing 2940 odd fps, the 180 will drift identically to the 215 to 1500 yards, with less drop. Beyond this the slightly higher BC of the 215 will start to edge it ahead.
As far as actually hitting your target in the first place, there is nothing in it between the 7mm RM with the 180gn Berger and the 300WM with the 215 Berger.
Yes, the 215 will have an energy and weight/diameter advantage that theoretically is an advantage in terminal performance, all else being equal. And it will have a slight theoretical barrel life advantage, about 6% more. But it does have quite a bit more recoil, around 30% more.
When you step up to the 230gn then it beats the 180 and 215 in the wind, at the expensive of more drop, and a bit more recoil again.
That puts some real numbers in this debate.
