The 7x57s have always pretty much had the same twist rates for the last 100 years-all made to stabilize the military 173d RN slugs. Hard to get a bullet much longer than that.
Just chiming in on the slight hijack here. I would agree with that statement about twist pertaining to the 7X57 Mausers made for miltary purposes - would not guess the same twist is uniform for commercial 7X57 rifles made since 1950 or so.
One thing is for certain, an old Model 93 and Chilean Model 95, and a later model (after 1900) that sit here, all in 7x57 with the stepped miltary barrels, are very accurate with bullets from 130 grains up to 175. Another testament that Mauser and his guys really knew what they were doing, and so long ago.
These three Mausers are unchanged with regard to the rifle itself (yes, turned bolts, nice stocks, drilled for scope, etc.) and as 100 year old miltary rifles seem amazing in their effectiveness. I would not dare rebarrel any of them.
As for 120 grain bullets in .284, they look quite short. However, some 120 grain SP made by Hornady (box is marked "Single Shot Pistol") shoot exceedingly well in the Model 95 and OK in the other two.
