Imagine what it must have been like in the old days when a gun didn't shoot so well and not having any real choice of powders, primers or bullets.
Tuff luck, just get closer to the target!
Seriously though, I've was told about how some folks would stress relieve their gun barrel in the old days by wrapping the gun up in canvas or burlap and burying it under ground for the winter. The freezing cold over a long period of time was supposed to help create better accuracy. Today we have that cyrogenic stress relief process to help accomplish that, both before and after machining if the best results are desired.