This subject has probably been covered in depth but thought to poll a few folks. My first reaction is that a .016 wall thickness is a safety concern if I wanted to shoot it rather than have a nice wall hanger.....,

Description is:

Bore diameter: left – .668, right -.667. Bore restrictions: left -.018 (mod), right -.006 (IC). Wall thickness: left -.016 (A small area near bottom rib, about 12″ back from muzzle), right -.023.

What is the consensus? Thank you

i would not shoot it

How far from the muzzle is the thin spot? What about the rest of the barrels, especially in front of the chambers?

old ed, a general gunsmith with over 60 years of experience says this regarding pre ww2 12 gauge guns with fluid steel barrels:

generally, .030 or more 8 or 9 inches down from the muzzles should be safe....090 or more in front of the chambers should also be safe for light loads...shooting anything less than that is risky...and shooting heavy loads in old guns is also risky.

as this gun sounds like a 16 gauge, be very cautious and seek professional help...

another option is to have it fit with a pair of briley 28 ga full length tubes...then you would have a safe alnd fun 28 gauge shooter.

The description call it back about 12" from the muzzle

how long are the barrels?

http://www.doublegunshop.com/forums/ubbthreads.php?ubb=showflat&Number=379803#Post379803

I think the wild card is I've seen guns (Parkers) where the bores were mint and untouched and they still were struck thin enough to where the minimum barrel wall thickness was in the .020 category. They hadn't been messed with, that's just the way they came. Now in my one personal case the .020 was about 22" down the barrel (6" from the muzzle). I'd think that pressures would be pretty low by then. FWIW, I fired RST 16 gauge loads out of that gun.

Just for what it's worth concerning thin barrels and pressures. A few years ago a customer had a DH 20 Parker with Damascus barrels, at close to the mid point on the right barrel it was only .014 wall, I recommended he have it proof tested, so I ran two proof loads through that barrel, about 18,000PSI each. No issues so I fired one in the left barrel, again no issues. I realize this really does not prove anything, but indicates a thin barrel might be able to stand a lot of pressure, and yes, the triggers were pulled with a line and me behind a wall of the buiding.

I am a big fan of "hillbilly proof". Did it to both of my damascus guns after having Keith Kearcher check them over years ago. Shoot really low pressure in them, and I'm very comfortable with the risk level. <6k in the 12 and <7k in the 20.
The 20ga has a min of .022 about 8" in on 28" barrels. My Flues money pit.

YMMV

"IF" one is Concerned about a set of barrels with good wall thickness at the breech end but thin at 18+ inches from the breech, shoot the load which gives the highest breech pressure commensurate with the overall desired ballistics.
You may for instance shoot two 1 oz loads which both reach 1200 fps muzzle velocity. If one of those loads has 3K "Less" "MAX Chamber Pressure" than the other, it's going to make it up some where else. I TRULY WONDER just where that might Be.

A note on proof, "hillbilly" or any other. Proof firing is necessary to get to after proof viewing. The test is only as good as the viewer and the viewing. Guns most usually don't disappear in a blinding flash and a resounding thunderclap. But, sometimes parts deform beyond their elastic limit. It is the duty of the viewer to "see" this deformation - via eyeballs or gages. The "hillbilly" method usually skips over the viewing. I'd bet sporting money that Dennis (above) gives every gun he proofs a really good viewing.

DDA

.016" is the thickness of the cover on a book of matches, or about the thickness of 5 average sheets of newspaper. To me that's not very comforting for a gun barrel. It may hold the pressure, but there is not much for margin of safety nor much strength to resist denting. There are too many good guns with adequate barrel thickness to risk shooting junk. Some people also get away for a long time driving on bald tires... until they don't.

This would be a good time for Doc Drew to put up that picture of the guy holding the blown-up shotgun with his hand missing a finger.

Miller, can you show us test graphs or point to references showing pressure rises from chamber to muzzle that illustrate your point regarding your statement about identical muzzle speeds and loads, lower pressures, etc. ? Thanks. Gil

Here you go Gil. "Smokeless Shotgun Powders: Their Development, Composition and Ballistic Characteristics" by Wallace H Coxe, 1931.

Ballistite is an early Dense Smokeless - higher chamber pressure
Schultze and DuPont Bulk Smokeless
DuPont Oval an early progressive burning powder - lower chamber but slightly higher at 4"



DuPont MX Smokeless was a Dense Multi Base Powder introduced about 1930. 25.5 grains was a 3 Dram Eq. and it was promoted as a 1 1/4 oz. Trap load. It was replaced in the 1954 with IMR PB.

This shows how pressure is higher at 18" with Dense vs. Bulk Smokeless

32 Gr Ballistite (1 1/8 oz. at 1232 fps = 3 Dram Equiv.)
Breech - 2.9 Tons per Square Inch (UK, Long) = 8624 psi
(2.9 x 1.5 = 4.35, 4.35 - .5 = 3.85 TSI, 3.85 x 2240 = 8624 psi)
2 1/2" - 2.2 Tons = 6272 psi
6” - 1.2 Tons = 3718 psi
12” - .81 Tons = 1602 psi
18” - .33 Tons
24” - .21 Tons

42 Gr Schultze 1 1/8 oz. at 1220
Breech - 1.69 Tons = 4558 psi
2 1/2” - 1.49 Tons = 3886 psi
6” - 1.36 Tons = 3450 psi
12” - .92 Tons = 1971 psi
18” - .55 Tons = 1178 psi
24” - .32 Tons

This is a pressure - time curve from Neil Winston - www.claytargettesting.com. The shot leaves the (30") barrel at about 3.5 milliseconds after ignition. The pressure is down to about 500 psi by 2 milliseconds.



More here
More here
https://docs.google.com/document/d/1F2sQuPm05IE4VWYYnCkvuXmYEzQoWd_SQgaAfUOZEFU/preview

Part of the discussion should clearly state where the thin spots are in relation to the forward hand. People pay extra for target barrels that have holes in them!

Posted here also in case the thread comes up in a future search. Note some barrels clearly are eccentric.



MEASURING WALL THICKNESS PROPERLY requires the expertise, time, and interest to do so.
One pass on one surface of the barrel is not adequate.

The 16 gauge has 28" barrels, the .016 thin spot is 12" from muzzle, balance is .023.

As the carpet dealer asks for a ruler, the assistant replies, "Which one? The one for selling or buying"

Thank you for the informed opinions

Note in the chart which Drew posted how the curves all cross between 3"-4" at which point the low pressure becomes the high pressure load & Vice-Versa. "IF" you push the same shot load to the same velocity you have done the same amount of work. That work in a shotgun barrel is accomplished by pressure. Thus if you lower it at one point you raise it somewhere else.
Now that said the "Peak" pressure occurs for a very short distance & extremely short time while the raised portion is spread out over virtually the rest of the barrel. in either case the pressure down the barrel is much lower than the max/peak pressure which occurs in the chamber.
Bottom line though is if you keep the same load & just change powders to drop the peak pressure you have not made it a bit easier on the gun other than directly in the chamber. These low pressure loads are actually most beneficial if you have a gun with very light breeches having thin walls over the chamber & particularly the junction of chamber & cone. In most guns this is not the case, particularly those built after the introduction of smokeless when this area was generally Beefed Up.

Get out a dial caliper and set it on .016 take a long look and If you're still brave and don't care about keeping all your fingers I say shoot away....

Drew, Miller, thanks for your time and effort. Gil

Under the theme of “God protects the clueless” (Psalm 116:6) with .016" MWT, I personally measured the wall thickness of a 1906 L.C. Smith 16g No. 0E with “Good Two Rod” Damascus at .016”, 14” from the breech which had survived 75 shots with 7/8 oz. at 1145 fps. (about 8000 psi) and 500 3/4 oz. at 1100 fps RSTs without rupture or bulge. The barrels have been retired.

Rocketman,
You are absolutely right. I wouldn't make much of a technical writer. My wife always tells me I skip over important parts of instructions when dealing with my boy. I skip what I think is obvious. Probably not a great trait. HB proofing without the viewing would just be stupid.

2-piper's several comments on this thread warrant re reading. They just make sense. I have been guilty in past years of searching for ultra low pressure loads that do the work of more muscular combinations. It is just common sense that to attain X velocity of a payload it requires Y energy. The difference being where the energy is released--in the chamber or further up the barrel.

The "Only" way to reduce total pressure is to reduce total ballistics, IE reduce the shot load, reduce the velocity OR Both.
It has often been stated that shooting a factory light 1 oz load (12ga) is just as hard on the gun as shooting a Hi-Vel 1¼ oz load because they both have the same allowable max pressure. This is only partially true. True they "MY" Reach the same Max pressure & point of max pressure may be no more than ¼" apart, but it will be closer to the breech in the 1 oz load so the walls will be just a bit thicker. The pressures for the rest of the bbl will be a bit lower, the strain on the action, stock & shooter will be less with the 1oz.