[4 Scale]

I have also been surprised at how accurate a poor bore can be, but believe it can be explained. My theory is, bore wear and corrosion tend to be fairly uniform around the circumference of the barrel due to the nature of the causes. The net result of either wear or corrosion is the removal of metal; i.e. nothing is added to the bore that can obstruct or alter the path of the projectile.

Calling a poor bore a "sewer pipe" while understandable I think does not capture the technical issue. What's repulsive about a genuine 'sewer pipe' is the residual substance. A worn and corroded "sewer pipe" Luger bore got that way because its original material was removed in a pattern that we perceive as ugly. By definition no additional material has been added to such bores. Rust is not an addition, by definition it is a transformation and a net subtraction in terms of mass.

And - due to the length of the bullet in relation to the relatively small size of individual corrosion patches such as pits, the corrosion itself will not degrade the bullet path or its spin. For the same reason, even in poor bores, gas cannot escape in sufficient quantity to decrease bullet velocity.

Phrased differently, as long as you can see rifling it doesn't matter how worn and corroded the bore is, it will be accurate.

I've thought about this a lot as I used to shoot rifles in target competition when younger and was trained to keep the bore scrupulously clean. Because of my "clean bore" heritage when I began collecting Lugers I shunned those with poor bores, sort of like the member who started this thread. Along the way I found a Luger with the notorious "sewer pipe" bore, at a price I couldn't resist, and was amazed at the accuracy.

Sorry for the long post - I invite challenges or corrections to this theory, just trying to understand how poor bores can be so accurate.