Re-barrel Luger Shooter

[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.

[sheepherder]

Originally Posted by 4 Scale

I have also been surprised at how accurate a poor bore can be, but believe it can be explained. My theory is, poor bores are caused by use (wear) and corrosion.

I invite challenges or corrections to this theory.

I offer neither. I do offer more information...

A Luger typically is marked with an 8,82mm [.347"] designation. That is a land dimension. A 9mm bullet is .355" diameter. That gives roughly a .004" - .005" depth of rifling groove. It would be reasonable to assume that the land would wear more rapidly than the groove (it is subjected to pressure/friction more than the groove). So the land can wear significantly more without affecting gyroscopic stability or velocity. Which equals accuracy.

...In theory...

To put this in perspective for non-machinists, a sheet of ruled notebook paper is .004" thick. I use pieces of notebook paper for my metalworking.