doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com What to do about pits?

This comes up so frequently that I've been working on a FAQ for the LCSCA site http://www.lcsmith.org/faq/faqhome.html
There were several helpful comments in response to a thread Dr Bob posted about 1 year ago, and I'd appreciate everyone's thoughts and thanks!


The management (or non-management) of pitted barrels is a difficult subject, with quite varied opinions among double gun shooters and gunsmiths.

1. Removing metal doesn't make a barrel stronger � duh
2. Most American doubles started with thick walls
3. It is almost impossible to accurately measure the wall thickness at the bottom of a pit
4. Pits are more common right past the forcing cone (a high pressure area = bad) and the distal barrel (where the pressure is much lower)
5. I've had barrels that looked terrible in the last 6-8 inches in which the pits were completely removed by honing of only .0015" ie. the bore enlarged from .729� to .732� and resultant wall thickness above .025�
6. Honing is only to be performed by an expert
7. There must be a good reason that the Birmingham Proof House requires removal of pits prior to re-proof
8. It is next to impossible to adequately clean a deeply pitted barrel
9. It is critical that further erosion at the bottom of the pits be stopped (see #8)
10. W.W. Greener
http://books.google.com/books?id=3HMCAAAAYAAJ&pg=PA353
and others
http://books.google.com/books?id=inQCAAAAYAAJ&pg=PA227
documented improvement in pattern density in a few guns that had been used extensively, one an estimated 80,000 shots. Greener thought this was from 'burnishing' the bore. This was of course before the era of plastic wads.
11. The claims that pitting either opens or tightens the pattern by 'retarding the wad' or some other black magic are unproven.
12. Any vintage gun with a �mirror bore� is very likely to have been honed at some time in the past

I'm pro-honing but many are not. With an American gun there is probably plenty of wall thickness to allow removing several thousandth of an inch of barrel wall.
I also believe if the minimum wall thickness is already too thin to allow removal of the pits, the barrels should not be used, with any load.

It's sad but true, and as you say. There is a point when barrels become scrap metal. I've lost sleep over nice but not top quality guns are beyond repair because there simply isn't enough metal left to make good again. Sleeving is an option sometimes but only if its economical.

Visually judging the depth of pitting in a barrel is very difficult. What look like craters can sometimes be polished out with a bit of emery cloth and a cleaning rod.

I think by answering a couple simple questions we could affirm or dispel some of the statements made concerning pitted barrels.

1. Has anyone presented evidence of a barrel burst where the proximate cause was pitting?

2. Has anyone presented evidence of a barrel burst where the proximate cause was honing of the barrels?

Major Sir Gerald Burrard in the second edition of The Modern Shotgun (1948) Volume 3, "The Gun and The Cartridge" discusses the causes of bursts, with illustrations, and inadequate wall thickness, metal flaws, and loading errors are the primary causes of NON-obstructional bursts. Even with Scanning Electron Microscopy (SEM) I think it would be very difficult to definitively identify the initial failure site as the bottom of a pit.

3 examples of bulges related to over-honing are shown here, and when the barrel bulge exceeds its elastic limit (and other stuff I don't understand) it bursts
https://docs.google.com/a/damascusknowle...nvwLYc-kGA/edit

Fox honed to .739" with resultant wall thickness of .018". Note there is no ring bulge at the distal end of the split excluding an obstruction (according to Burrard)



The 'mirror bore' sure looks nice though

Brother Drew, hard to imagine someone would hone those Fox barrels without first knowing wall thickness, but I guess it happens all of the time.

Thanks for the very thorough research on your site, something that all should read.

I hate to post it because it is like torch colors but I knew a guy who colored epoxy black and pushed a cap plug through the rough tube moving a bunch of epoxy ahead of the cap plug. It looked good enough to fool people but did NOTHING about adding strength to the hole. BEWARE!!

bill

Don't buy them in the first place.

I read of one person's solution in regard to preventing further deterioration, but I haven't tried it yet. His method was to coat the bores with an automotive "Rust Reformer" product. Then, after drying, he would polish out the barrels. As I read it, the product contains phosphoric acid, and is able to stop further rusting by converting the rust to black oxide. The big caveat was that extreme care was needed, as any spilled on the exterior finish would prevent future bluing in those spots. Evidently he tried, but I'm not sure if he tried rust bluing or a cold blue solution.

Regards
Ken

Drew, if those Fox barrels were 0.018" after the honing, they would have only been 0.0225" before honing, which I believe is too thin at the front of the fore end?
I sometimes wonder if the case of honing is not overstated. To hone a barrel significantly requires special equipment, such as a Sunnen hone. How many gunsmiths have such a piece of equipment? With anything less than a specialized hone, you can spend a very long time removing a miniscule amount of metal.