Barrel Wall Thickness Question and Problem

[SuperCracker]

Ok, had an........ "incident" in the shop and need some input.

Was drilling a front lock bolt and the vise I had the stock secured in slipped on the drill press table before I started drilling (didn't notice the movement) and I just barely caught the bottom of the barrel ahead of the breech. With the combination of large press, long press handles and brand new super sharp bit I didn't feel it and it continued right on through........... (I can't possibly be the first person to do this. )

It's a 12ga (.725bore), full round smoothbore barrel. The nick is 2 1/8" from the plug face so it should be just a bit ahead of the ball/shot column when loaded, it's .032 deep. Leaving a spot wall thickness of .1455" (vs .1815" on the opposite side)at the nick.

Naturally I'll go ahead and drill a vent and test fire it some before using it for anything, but what are the opinions of those of you with vastly more experience and knowledge than me?

Junk it and buy another?
Cut it off and make a big wrist breaker of a horse pistol.
It's fine, use it?
etc.etc.

[keweenaw]

Simply forget it.  Even rifle barrels that are operating at much higher pressure can be notched deeper than that with no ill effects.  Obviously there is a limit to how thin a barrel can be anywhere but .1455 is probably about what lots of shotgun cartridge gun wall thickness are at the front of the chambers and they are generating considerably more pressure than a black powder muzzleloading fowler.

[Frank Savage]

That´s a pity...

Well, the rifle is gonna have 3,5" shorter tube, if can be done. Cut it at the nick, rebreech. The wall thickness is on the pretty low "just enought" side even without the nick. No matter what the steel is, the nick makes inconsistency in tension distribution. For sure the material will have tendency to elongate on the lower part of the barrel, creating stress in the upper portion. Hard to say if after several, or after several dozen shots.
Yes, the barrel is a wristbreaker, if one counts near- or full-amputation as a "break". Played with several mild steels and wall thicknesses some years ago, trying to figure which can be used for a barrel and what the most dangerous machining marks, flaws and oops are those which makes man sniffing flowers from the less colorful side. And such a nick is gonna make someone ugly problem.

Looking for paralell with a dovetail is false, because no sane person would put a dovetail on such a thin-walled barrel less than foot from the breech (I hope).

Edit
in reaction to snyder:
We know nothing about the material specs and grade used on that barrel. So such a paralell is absolutely OFF!!! AND one of most dangerous statements, which can be said.
To hold securely and repetitively pressures of BP, you need 4,5-5 mm (1/6"-1/5") of about 1018 steel-wihout the tread. But the same you can hold easily by only 1/25" of properly heat-treated 4130 or 4140 alloyed steel. The ultimate tensile strenght is not what counts here-it´s the safety margin to actual yield strenght, what makes the barrel safe or unsafe through more than one or very few shots.

[SuperCracker]

Well, the rifle is gonna have 3,5" shorter tube, if can be done. Cut it at the nick, rebreech. The wall thickness is on the pretty low "just enought" side even without the nick.

.18 and .14 at that point would be very thin for a rifle. But this is a fowler. So the pressures should be considerably lower, correct?

It's tapered all the way down, so no trimming it off or I would have just done that. sadly.

[Frank Savage]

Then ditch it for this project, rebreech and use on other project.
Yes, fowlers have lower pressures, sometimes as low as about 12-14 000 PSI. But you canīt ever count it around the breech. The breech area and about 12" ahead must withstand anything what any reasonable (read: double) charge of any sane powder grade (read 3F, since it burns fastest) can do there. It makes no sense to make a thing which is just OK now, but makes a pipebomb with other lot of powder with slightly faster and hotter burn rate.
Or having a "obstruction" like a small piece of grass leaf in the barrel, not knowing that and the watch rests of own hand...

[Don Getz]

Frank Savage.......have you ever looked at some old guns, barrels in particular, and noticed that many of them have a groove
in the bottom for that front lock bolt.    While those numbers shown for this smoothbore would appear to be on the short side, let me tell you of some proofing we did on an .812 (13/16") straight barrel with a 50 cal. rifled  bore.  We proofed them using
a special plug to hold a fuse.  300 grains of FFF, and two patched balls.....can you believe that?  The barrel walls on these
barrels were less than .150, and, by the way, they were made of 12L14 steel.  On the other hand, we don't know what this
smoothbore barrel was made from, could have been made from seamless tubing, which I don't like, that's just a personal thing,..............Don

[FlintFan]

Yes, fowlers have lower pressures, sometimes as low as about 12-14 000 PSI.

Whoa!...that's modern 12 gauge, 3" magnum pressures you are quoting there.  With a 3 to 3 1/2 dram load in a 12 bore MUZZLELOADER, you would be lucky to hit the 6,000 psi range, on the high end.  That's using FFF and a 1 1/4 oz of shot.  

I would trust Mr. Getz's experience.  If you have any doubts, proof fire the barrel a few times to put your mind at ease.  

[SuperCracker]

On the other hand, we don't know what this
smoothbore barrel was made from, could have been made from seamless tubing,

Oops. Should have mentioned that this is a barrel Colerain made for me. So, while I don't know what alloy he used I doubt it's seamless tubing.

That's a crazy proof test Don. I would have bet against that barrel surviving for sure.

[JDK]

Shane, Colerain uses 12L14....same as Getz.  Enjoy, J.D.

[PPatch]

Majority of Colerain barrels are 12L14. Of course I have no idea what your special order barrels are made of, but Colrain does. My Rice B weight has a lock screw groove on its bottom too, pretty shallow. Like you I did not realize it until later as the drill bit did not tell me as it tunneled under the barrel, no feedback. For my project that will not be a problem.

dave

[Don Getz]

Getting that front lock screw at the right place used to be difficult.     I use a depth guage to find the bottom of the barrel
inlet.  I then mark this depth on the lock panel and drill that front lock bolt right at the bottom of the barrel inlet, the clearance
drill usually will open a line across that bottom flat, almost touching the barrel.  If it does touch the barrel it is no problem to
file clearance for it.   Sure makes it easier to fit the ramrod.......Don

[davec2]

I would proof the barrel but would certainly have no problem in using it as is.  I've put deeper notches in a barrel to pass a lock bolt on purpose.  Besides, Frank's opinion notwithstanding, this is not a sharp edge notch nor is it a circumferential groove around the entire barrel.  It is, rather, a radiused oval of material removed in one very small spot and is only at its thinnest in the very center of that small spot.

I would not give it a second thought.

[kutter]

Scroll down to the second image 'Recomended Wall Thickness' Note this is on damascus steel bbl.
Further down in the article are some other wall thickness measurements given just ahead of the chamber in cartridge shotguns.
Thought this may be helpful

https://docs.google.com/document/d/1LFnSG34k3mBhLEjEgU267wAlIa215MNVQZhIiY62Hx4/edit?pli=1

[Dave B]

I wouldn't hesitate to use the barrel. Here is the example from the colonial period. The barrel is a .62 cal and has a breach equal to a "D" Profile. note the two notches in the barrel from the first lock it was matched with and the second one once they restocked it  using a smaller lock and again notched the barrel. It held together for over 100 + yrs  on a wrought Iron barrel hammer forged barrel. You will be safe with  12L14

[SuperCracker]

Thanks everyone for the info. I knew I could count on this community for solid input. Pending hearing back a veto from Colerain I'll almost certainly use the barrel but for a gun for me that would never be sold. Barrel strength aside I would just never want a gun with my name on it to be taken apart and have someone see that screw up. I had been wanting to build a smoothy and have just one gun to use for pretty much everything anyway.


Frank: Thanks for chiming in. I agree with what you're saying and know what you're talking about, however I think the existence of long used and long surviving originals of inferior materials with deeper notches indicates that there must be more to the picture. I think with the pressures we experience in these guns it would tend to never create the stresses that would be cumulative in a modern gun. I also remembered my notes about proof testing a mid 19th century German damascus 16ga that was badly pitted and very very thin and I was unable to blow it up. I did that some time ago and had forgotten about it.


JDK. & PPATCH: I figured that was the case but I didn't want to speak for them. I didn't specify anything special material wise when I ordered the barrel so I really doubt he would have used anything weird. I REALLY doubt he would have taken it on himself to use an inferior material.


Don: Being paranoid about getting into the RR hole (I'll give you three guesses how I got paranoid about that  ) I carefully marked it out using a virtually identical method, put it in the vise on the press, then got distracted (she who cannot be ignored came out to the shop) and came back to the press 20 minutes later then started to drill the hole without realizing I had failed to tighten down the back side of the vise on the press table. The vibration rotated it around a tiny bit.  Dumb mistake that will not be repeated. Thanks for weighing in, your experience carries much weight.


Kutter: Thanks a ton for that link. That's good info that is definitely going to be obsessed over, absorbed and incorporated. Building fine double guns for wing shooting is my eventual goal. I have a lot more skills to hone and accumulate before I jump into that. But dimensions for the tubes are a big part of getting the balance right. I knew data like that had to be floating around out there, I have just been unable to run into it.


Dave B: Thanks for the pic. I KNEW I had seen pics of notched originals but I never saved any and couldn't come up with one now. So I was doubting my memory. The notch in my barrel is no where near that deep.

[Dphariss]

I wouldn't hesitate to use the barrel. Here is the example from the colonial period. The barrel is a .62 cal and has a breach equal to a "D" Profile. note the two notches in the barrel from the first lock it was matched with and the second one once they restocked it  using a smaller lock and again notched the barrel. It held together for over 100 + yrs  on a wrought Iron barrel hammer forged barrel. You will be safe with  12L14

Actually a notch makes a stress riser in 12L14, not good in an already heavily stressed bar of steel.
In the real world the wrought iron barrel, properly welded and of good iron which is a tough material, is better.
IIRC the welded "best iron", relatively thin wall, 58 Springfield Rifle Musket barrels were proved with 200 gr of musket powder and a Minie spaced 2" off the powder. If the barrel failed at the weld the person who welded it was charged for the barrel. The gov't did not expect them to fail. They had a committee that inspected ALL the failures to determine WHY it occurred. The responsible workman then took it in the paycheck.
Newer is not always "better". While high quality hot rolled 4150 is obviously better, its the state of the art in barrel steels right now. Cold rolled steels?  This one in particular is state of the art for making screws in automatic screw machines. The requirements for this have nothing to do with gun barrels.
Dan

[SuperCracker]

In related news, the weapons grade brain F*#t I apparently had cleared up and It finally occurred to me to go and measure the wall thickness on my original 12Ga ML double. 

In the same spot on that barrel it's .151". That's only ~0.010" difference, and that's on a 160year old Damascus barrel I shoot all the time. again...... 

[Lutes]

I don't want to steal the post here but this leads me think that they have been a lot  of modern 12 gauge shotgun barrels cut off at the end of the chamber and bored and threaded for 7/8 breech plugs. This leaves approx. .100 wall thickness at the bottom of the treads. I know I have shot one of them for several years. Now that I am older and have thought about this for a while makes me wonder? What are your thoughts on this. I still see a lot of people shooting them?

[Bob Roller]

I wouldn't worry too much about that breech in a modern shotgun barrel
unless extreme loads,way beyond those normally associated with a 12
gauge are used. The load of shot and wads will move forward much easier
than the breech plug will move backward.
I'm assuming that the barrel may be one made for nitro powders like a model
37 Winchester or some other.Listen to Dan.
Bob Roller

[Lutes]

Bob they are Remington 870 barrels

[Bob Roller]

The 870 barrels should work.I think a 7/8x14 thread uses a 3/4" hole to establish the needed depth
of the thread or better yet,the next drill size that is .015 smaller.

Bob Roller