Barrel Wall Thickness

[Jim Kucaba]

Originally Posted by Robin Lewis

Thanks Drew, I incorporated this information and some of the other comments to improve this FAQ.

Thank all for your input, it helped too.

Robin ... What a great illustration ! ... I hope everyone prints several copies for future reference ... THANKS !

Jim Kucaba ... AriZOOna Cactus Patch ... Email: JimKucaba@aol.com

[Jean-Paul Lavalleye]

Following up on Drew Hause's above post regarding The Hunter's Encyclopedia from the German proof house, is there data of actual measurements, current or old, of Parker barrels minimal wall thickness at end of chamber, regardless of length, for 12, 16, 20 & 28 gauge guns?

I currently own three Parkers on which I've made this measurement using Hosford and Co. barrel wall thickness gauge. The chamber minimum wall thickness data for these is as follows:

1.) BH 12b. on a no. 1 frame, R ≥ 0.088, L ≥ 0.094 (Damascus barrels)
2.) GH 20b. on an 0 fame, R ≥ 0.100, L ≥ 0.092 (Damascus barrels)
3.) DHE 28b. on an 0 frame, R ≥ 0.084, L ≥ 0.076 (Titanic steel barrels).

All of these have been shot for many many years (not by me) and measure up well in terms of min wall thickness and bore diameters. Kirk Merrington tells me that, in his experience, Parkers and other American guns tend to have wall thickness at end of chamber that are considerably less than found on English or German guns (in the 0.080"-ish range). Yet this does not seem to be problematic. The Sherman Bell articles of a few years, in the Double Gun J., regarding the strength of Damascus barrels would seem to support this conclusion.

Is there data somewhere that would show how low you can safely go with these thicknesses (or how low Parker went when they were making these guns)? I am currently looking at a 16b. Parker on an 0 frame where that minimum thickness (for a 2.5" chamber) is 0.068" on one chamber and 0.071" on the other, with all other measurement being fine; bores at 0.667, min barrel wall thickness at 0.030." This gun has very obviously been shot quite a lot. Is it safe?

[Double Lab]

JP,
I looked at that 16b you are referring to on Sat. and without any way of measuring other than by my eye they looked just fine to me. Your measurements of the BWT seem to me to be quite acceptable and the bore diameter is well within specs. I would have no problems shooting it with low pressure handloads or RST loads. Have the barrels been blued? I did'nt examine them that closely but that is a sweet gun. I was really interested in the smallbore P grade with twist barrels.

Daryl

[Bruce Day]

So if you start with typical Parker wall thickness of say .032 for all gauges ( heavy waterfowl guns were thicker) and honing once often takes .008, then you have .024, and then a second hone to clean the bores because used gun buyers like shiny bores because it shows the gun was not used much, another .008, and you are at......


I'm aware of a 20ga Parker ruptured barrel in the forward 1/3rd, wall thickness .006, but those bores sure were shiny. No obstruction.

[winplumber]

Bruce Is not .006 below the mwt. of .025 that some say is ok ?

[TARNATION !!!]

Bruce: On that 20 ga, based on the .008 loss per honing, those barrels would have been honed at least 3 times to get down to .006 if starting at .030 if I got the math right. This leads to my continuing education questions.

Does honing serve a practical purpose verses a cosmetic purpose?
Does light pitting cause problems for continued shooting?
Hypothetically, does a single deep pit [let's say it leaves .020 at that spot] have the same potential for barrel destruction as the honing to remove it or would honing the entire barrel be far more problematic?
Finally, is there a means to fill a pit and leave the bwt alone, as opposed to remove steel to the depth of the pit thereby reducing bwt over the entire barrel length?

Drew: The barrel schematic shows no forcing cone. I'm wondering about bwt around the cone. Thoughts?

Thanks,
Jack

[Bruce Day]

Jack, here's my take on it. I know others have studied the issue also, and I am a big fan of the Bill Murphy philosophy of "don't mess with them".

1. No, except that unpitted bores are easier to clean. So just scrub more.

2. No

3. Don't think so. Would you rather have a small single isolated potentially weak spot or would you rather have the entire barrel length potentially weak?

4. Don't know, other than a full length liner, which is a drastic and expensive remedy.

[Drew Hause]

"Is there a means to fill a pit?"

I've discussed with a few TIG specialists, and no.

[TARNATION !!!]

Drew: So we can rule out TIG welding. I have often wondered if some of the advanced epoxy resin systems might fill a pit without resorting to welding. Is there something inherently wrong with epoxy/steel combo that is made flush to the inside of the barrel?? Don't know, just asking.
Cheers,
Jack

[VH20]

Bruce,

Your example of taking .008 from the BWT for a first "honing" seems extreme. To remove this much metal, usually they would be reamed instead of honed, but that's just academic to this discussion. The point I want to make is that using your example of taking .008 from the BWT would mean adding .016 to the bore dia. So, a typical .730 bore would now be .746 after one reaming, and a second would make the bore a whopping .762.

I have found that reaming in steps of .005 over bore dia. often cleans up most pitting, and if not, another .005-over usually will. In the first case, you only take .0025 (two-and-a-half thousandths) off the BWT, and in the second, still only .005. If necessary, we could go up another .005 and now be .015 over original bore dia. (.745), yet after three reamings still not have taken off quite as much as your example of one reaming (.0075 vs. your .008). There is a reason bore reamers are typically sold in .005 increments. But you have to remember that reaming x-thousandths from the bore only removes 1/2x-thousandths from the BWT.

All that said, I agree with you and Bill. Really not much reason to fool with it in the first place, and I usually don't.

Jim