No kidding. I recently renovated the bathroom in my old shotgun shack, which involved tearing out part of a wall, and replacing it.
The inexpensive method of addressing that issue is to rip modern wood to provide tack strips which bring the replacement lumber back to 4". Air powered staple guns are heaven sent.
Try tearing out even somewhat rotted oak real 2x4s. My brother did mention that 6 lb sledge hammers weren't typical framing tools.
/johnny
When 2x4’s were 2x4’s — most weren’t. The lumber was sawn to 2x4 — but, there was no standard for the moisture content when sawn. If sawn from green logs, a 2x4 would shrink more than if cut from air-dried logs. The amount of shrinkage varied by type of wood too. The modern practice of kiln drying the rough-cut lumber, then planing it to size, yields more uniform material. That makes it easier to work with.
Of course, the old-time carpenters knew how to deal with the small differences owing to shrinkage. Mostly, they did that by ignoring it. For instance, one of the (few) benefits of plaster-on-lathe is that the framing doesn’t have to be very precise.
Real 2 X 4s? Then they must have been unmilled. Milling takes a quarter-inch off each of the four sides, leaving the standard 1 1/2" X 3 1/2" dealie.
I have seen real, unmilled 2 X 8s: a full two inches thick. Needless to say, they were hammered into place a long, long time ago.