doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com How much is too much pitting?

A liitle research and you'll find out easurement of barrel wall thinkness is very easily and accurately done with a wall thickness gauge. Also that bores are often eccentric with the outside diameter. Obviously from your post you don't have anything but a mike or vernier to measure the outside diameter of the barrels. You probably don't want to spend the money for a competent inspection but that's the only way to go.

And the measurement of "pit depth" is going to be even tougher.

Cherry Bomb,

I am trying to decide if I can shoot the barrels safely the way they are. I know it is hard to tell without an inspection.
Otherwise, a specialist's opinion might be the only "large" expense in making this gun shootable.
Buying the tools to do such measurements is significantly more expensive than sending he barrels out.

Sliver

"jOe, does the pitting stop with the oiling of the gun? "


I am not sure if oil will stop the pitting (rusting), but boiling
the barrel may.
Casey

There is ages-old method of estimating depth of pitts and determining which pitts are especially deep. It can be called "oil-film" method. It consists of spraying oil down bores and letting it flow out to more or less uniform layer. One can immediately see where deeper pitts are because surface tension of oil will not be enough to maintain flat surface on oil film. Instead, deeper pitts will be seen as depressions.

Attempts to estimate thickness of oil films can follow any method you have access to for measurement of film thicknesses, either directly or indirectly (say, on surrogate metal surface).

Would never suggest this is replacement for good meassurement of wall thickness or bore scope, but, it can sure give some usefull apprasals of pitts in bores.

Niklas

I just showed the barrels to a local gunsmith and he thinks they are shootable, the pits did not seem deep to him. i might still send it out for more assurance.

Casey,

I will be rustblueing the barrels eventually and boil them as one of the steps to stop the rusting process. A coat of oil in the meantime precludes oxygen from coming in contact with the metal and stop or slow down the process.

Niklas,

That is a nice tip to know. I guess, the thicker the oil (the higher the surface tension), the bigger pits it can cover. The trouble with this method is that one may deal with a deep narrow pit that might not show whereas a larger shallow pit may show through.

Sliver,

So far, ALL of many pitted barrels I have examined closely had more or less equidimensional pits, often with irregular edges. Generally these seem to be of consistant depth, which oil film method shows well. It is pitts that are deeper that make me wonder about slag inclusions, focused pitt formation, etc., things that can lead to especially weak areas and even holes. Steels from late 1800s and early 1900s are well known to have slag inclusion impurities and for these to become centers of electrolytic corrosion and perforation pitts. Bad news, those focused pitts!!

I have now and then seen what I thought was either streaks of leading or pitts that had formed under leading. I would expect they are wide enough for oil-film method to be useful. Some grooves or long scratches, lengthwise in barrels, make me think of something hard having been shot, like early steel shot, maybe in inadequate wad cups.

IF I were to see really narrow pits, not lenghtwise in bore, I might immediately wonder if there was a crack or long, smeared-out impurity (slag?) in barrel metal. Both just might cause me to reject that gun. If deepish pitts are not enough cause for concern, suspected cracks or extended impurities are even more.

Lars

More reason to have Mike Orlen see them.
I will try to post some pics and see if I can show the pits.

Sliver

I am sure that oil will not harm the gun, it will help.

I have about 12 old SxS barrels from a friend that were
covered with rust, just for the heck of it I did wire-wheel some and boiled them to see what will happened. Now they look almost
black.
The boiling process turn the rust into black oxide.
I could be wrong

Casey

I have a British 410 hammer gun with several generations of proof marks, the latest being 1989 vintage. Oddly, the gun is proofed for 2-3/4" shells. I lengthend the forcing cones and shoot standard 3" shells through it. The gun has an enormous and deep pit on the outside of the barrel under the forend. I am certain the pit pre-dates the 1989 proof. I've probably shot 3-400 3" shells through this gun without problems. The reason I'm bringing this up is that .410's typically have much higher chamber pressures then larger gauge guns.
Steve