I acquired a McMillan stock that was on a Sako 75 in 30-06. From what I’ve read this would be considered the IV action.

Are the “magnum” actions longer? Like would the stock fit on a 7mm rem mag? Just wondering as it might give me a few more options for finding a suitable rifle to put it on.

You are right in that the IV is the ‘06 length action.

I = 223 length
III = 308 length
IV = 30-06 length
V = magnum length
SM = short magnums

* there were some oddballs aswell. Such as the ppcs which were built on the III action but with a spacer in the magazine, and the early short mags were built on the V action with again a spacer in the mag.

Thanks for confirming. I had thought so but I didn't know if they differentiated actions by the bolt face as well like where IV and V would be the same length but one having a magnum bolt face.