Barrel Value, Pitted versus Clean.

[Pay Dirt]

How would lightly pitted barrels affect gun value?
Bore end? breach end? Mid barrel? How would their location in a barrel affect safety/shootability?

[J.B. Books]

I think each gun has to be evaluated on it's own plus' and minus' and pitted bores are always a minus. As far as shootability, to my mind the degree of pitting has to be weighed against the barrel wall thickness as a semi objective measure. The thicker the barrel walls the better. As far as pressure, pressure is highest at the breech and drops rapidly (in a few inches) as the shot charge travels down the bore. Remember Sherman Bell shot overloads near 19000 psi in 15 "wall hangers" some with severely pitted bores and none blew. Of course you don't want to find the first one that does. One of my favorite hunting guns has pitted bores, they take more time to clean but they shoot fine. If you really like a gun otherwise and the barrels are good and stout I would not pass on it if I liked it. I don't know what the discount would be for pitted bores but one idea is to find out what the going rate is to have them cleaned up by someone like Brad Bachelder and use that as a negotiating tool trying to get the seller to discount all or some of the barrel work.

I think Chuck H has a good point on the DoubleGun board, look at the highly engraved Fox in the picture, as he said nobody worries about the deep pitting ;-) on the outside of the breech of that Fox.

http://www.doublegunshop.com/forums/...=268477&page=4

[Big Friend Ten (BFT)]

I agree with the above by Mr. Books. Personally, I like bores hones or reamed so that no pitting remains. That is what the British proof houses do. With all pitting removed the Minimum Barrel Wall Thickness can be accurately measured.

MBWT is the key to determining if barrels are safe to shoot. The proof houses measure before and after firing proof loads. If there is an increase in bore inside diameter, or decrease in MBWT (necking), from the proof loads then the natural elasticity (Youngs Modulas) has been exceeded past the yeild poing and permanent, plastic deformation has occured.

Once I know the MBWT, I have a good idea what pressure should be safe in a Damascus barrel. If I cannot see the bottom of the pits I have no way of accurately determining the MBWT.
-- Note: Flecking or very shallow pitting inside barrels caused my surface rust should not be a problem. I use Flex Hones to clean that out.

Below is a simplistic explanation of this from Wikipedia...

From: http://en.wikipedia.org/wiki/Deformation_(engineering)

Elastic deformationThis type of deformation is reversible. Once the forces are no longer applied, the object returns to its original shape. Elastomers and shape memory metals such as Nitinol exhibit large elastic deformation ranges, as does rubber. However elasticity is nonlinear in these materials. Normal metals, ceramics and most crystals show linear elasticity and an smaller elastic range.

Linear elastic deformation is governed by Hooke's law, which states:

Where is the applied stress, is a material constant called Young's modulus, and ε is the resulting strain. This relationship only applies in the elastic range and indicates that the slope of the stress vs. strain curve can be used to find Young's modulus. Engineers often use this calculation in tensile tests. The elastic range ends when the material reaches its yield strength. At this point plastic deformation begins.

Note that not all elastic materials undergo linear elastic deformation; some, such as concrete, gray cast iron, and many polymers, respond nonlinearly. For these materials Hooke's law is inapplicable.[3]

Plastic deformation See also: Plasticity (physics)
This type of deformation is irreversible. However, an object in the plastic deformation range will first have undergone elastic deformation, which is reversible, so the object will return part way to its original shape. Soft thermoplastics have a rather large plastic deformation range as do ductile metals such as copper, silver, and gold. Steel does, too, but not cast iron. Hard thermosetting plastics, rubber, crystals, and ceramics have minimal plastic deformation ranges. One material with a large plastic deformation range is wet chewing gum, which can be stretched dozens of times its original length.

Under tensile stress plastic deformation is characterized by a strain hardening region and a necking region and finally, fracture (also called rupture). During strain hardening the material becomes stronger through the movement of atomic dislocations. The necking phase is indicated by a reduction in cross-sectional area of the specimen. Necking begins after the ultimate strength is reached. During necking, the material can no longer withstand the maximum stress and the strain in the specimen rapidly increases. Plastic deformation ends with the fracture of the material.

[Dean Romig]

Tennis anyone??