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Posted By: Rookhawk Minimum Wall Thickness Revisited - 12/14/11 10:44 PM
I heard an interesting one today from Dan at William Larkin Moore.

His claim was minimum walls of anything at or above .020" was fine (not marginal) for 2.5", vintage pressure shells.

His claim was minimum walls of anything at or above .025 "was fine (not marginal) for 2.75", modern pressure shells.


Both those statements assume the gun is within proof and shooting the prescribed shell for that gun.

I'll now wait to read your responses since I'd not heard this distinction before.
Posted By: Terry Lubzinski Re: Minimum Wall Thickness Revisited - 12/14/11 11:51 PM
Yikes!!!!!!!!!
Posted By: AmarilloMike Re: Minimum Wall Thickness Revisited - 12/14/11 11:55 PM
In either case it makes a big difference where that minimum wall thickness is. If it is 3" from the muzzle I wouldn't mind shooting the 2-3/4" shell with 20/1000th wall thickness. If is it 3" from the forcing cone I don't care to shoot either gun.

Best,

Mike
Posted By: HomelessjOe Re: Minimum Wall Thickness Revisited - 12/15/11 12:21 AM
Sounds fine if you're the seller.
Posted By: Rookhawk Re: Minimum Wall Thickness Revisited - 12/15/11 12:46 AM
AmarilloMike,

Valid point. Would you argue minimum wall thickness after the first say 20" of barrel is almost irrelevant? Wouldn't the actual wall at 8" from breech being greater than say .040" be far more important?

Has anyone gone through the effort to figure out safe minimums at each point from the breech so that there is something more reliable than an overall minimum thickness number?
Posted By: Ben Thayer Re: Minimum Wall Thickness Revisited - 12/15/11 01:41 AM
Everyone has to decide what minimum they want to wrap their hand around and get their face close to.

Assurances are easier to come by than guarantees.
Posted By: PA24 Re: Minimum Wall Thickness Revisited - 12/15/11 01:46 AM
Originally Posted By: Rookhawk
Has anyone gone through the effort to figure out safe minimums at each point from the breech so that there is something more reliable than an overall minimum thickness number?





From DuPont Powders 1933.....


For the first 8-10 inches, most factory barrel wall thickness is 35-45 thou min............butchered with anything less, I'm not interested in shooting it..........

There are quite a few pressure charts out there, PeteM will probably be along shortly and post one for you.......these show how rapidly the pressure falls off in a shotgun after the first 8 inches or so........
Posted By: steve white Re: Minimum Wall Thickness Revisited - 12/15/11 04:08 AM
WHAT OF MINIMUM CHAMBER WALL AND FORCING CONE THICKNESS?
Posted By: AmarilloMike Re: Minimum Wall Thickness Revisited - 12/15/11 06:00 AM
Originally Posted By: steve white
WHAT OF MINIMUM CHAMBER WALL AND FORCING CONE THICKNESS?


http://www.doublegunshop.com/forums/ubbthreads.php?ubb=showflat&Number=224972&page=1

Originally Posted By: AmarilloMike
Originally Posted By: L. Brown
But most gunsmiths that specialize in doubleguns, I think, would like to see a minimum barrel wall thickness of .100 at the mouth of the chamber.


I sure have a lot of doubles with original chambers and forcing cones with wall thicknesses way below .100" at the end of the chamber.

Fox A grade 16ga, 26" barrels, 2-7/16" chamber, 0.085" and 0.086" minimum wall thickness at the end of the chambers, .734" and .734" diameter at the end of the chambers, 5/8" long forcing cones, #4 barrels, gun weighs 5lbs 9oz, serial 302XXX.

Parker VH O Frame 16ga, 28" steel barrels, serial 134XXX, 2-9/16" chamber, .082" and 0.085" minimum wall thickness at the end of the chambers, 0.730" and 0.732" end chamber diameters, 3lbs 2oz unstruck barrel weight, gun weighs 5lbs 14oz.

Fox XE 16ga, 30" barrels, serial 301xxx, .072" and .080" minimum wall at chamber ends, 2-7/16" chambers, .733" and .733" end chamber diameters, gun weighs 6lbs 3oz

Parker DHE 16ga, 32" steel barrels, serial 212XXX, 0.090" and 0.092" minimum wall thickness at chamber ends, 2-9/16" chambers, .735" and .736" diameter at chamber ends, barrel unstruck barrel weight 3lbs 11oz, gun weighs 7lbs 4oz.

Lefever H grade 16 gauge, 28" twist barrels, .090" and .092" minimum wall thickness at chamber ends, 2-5/8" chambers, .729" and .728" diameter at chamber ends. Gun weighs 6lbs 4oz

Ithaca Flues Grade 4E 16 gauge, 28" Krupp fluid steel barrels, 0.091" and 0.092" minimum wall thickness at the end of 2-5/8" chambers, daimeters of .728" and .730" at the end of the chambers, gun weighs 6lbs 6ounces.

Parker DH 12 bore, 28" Damascus barrels, 1 frame, .086" and .090" minimum wall thickness at end of the 2-5/8" chambers, gun weighs 6lbs 14oz. Serial #84XXX, My Skeets gauges are in capable of measuring the diameters at the end of the chamber.

Bissel Birmingham boxlock, 20 gauge, 25" steel barrels, made in the 1920s, .084" and .092" minimum wall thickness at the chamber ends, 2-1/2" chambers. My Skeets gauges are in capable of measuring the diameters at the end of the chamber. Weighs 5lbs 7oz.

Best,

Mike

Posted By: AmarilloMike Re: Minimum Wall Thickness Revisited - 12/15/11 06:04 AM
Originally Posted By: Rookhawk
AmarilloMike,

Valid point. Would you argue minimum wall thickness after the first say 20" of barrel is almost irrelevant? Wouldn't the actual wall at 8" from breech being greater than say .040" be far more important?

Has anyone gone through the effort to figure out safe minimums at each point from the breech so that there is something more reliable than an overall minimum thickness number?


I beleive the .020" minimum wall thickness in the last 1/3rd of the barrel is about repair of dents. Maybe Joe Wood will pipe in here about Greener taking out his pocket knife and slitting the last half of barrel after shooting several loads thought it.

Best,

Mike
Posted By: PeteM Re: Minimum Wall Thickness Revisited - 12/15/11 12:16 PM
Originally Posted By: Rookhawk
Has anyone gone through the effort to figure out safe minimums at each point from the breech so that there is something more reliable than an overall minimum thickness number?


Not to my knowledge. At least nothing that has ever been published. Ultimately the gun designer has to know what material will be used in the barrel. Once that is known everything else follows.

Now about the DuPont chart...



I have been through this booklet several times. I am 100% sure that they state they used lead crushers to obtain their data.

To the best of my knowledge, piezo was not in common use then. It would have been easy to create a probe that could be correlated to lead, copper or whatever you choose. The equipment, ie oscilliscope, they used was primitive by today's standard. Limited to about 10mhz, single trace, no memory, etc...

There was a serious discussion in the literature circa 1915 about the lead crusher standard of the day. It was fully recognized that lead crusher was a flawed method. Mainly because it had a built-in inertia which prevented the capture of smaller values. This shows in the chart, they stop at 10" from the breech. Not because they considered the data irrelevant, but because they knew the lead crusher system would not give them accurate information below about 3,000 psi.

As Larry B has pointed out in the past. They had so much data based on the lead crusher method, they could not bring themselves to simply walk away from it.

For my own use, I will not knowingly fire a gun that has had the chambers tampered with. I measure my guns to be sure of wall thickness. I do not trust a dealer nor those in their employee with my fingers.

If I want to shoot the heaviest loads, I have a Baikal for that. Built like a tank!

Pete
AM is right. It's not bulging or bursts that are the real problem, it's how much life is left in the bbls.

Thin walls cannot be repaired, so a dent or a bulge in the wrong spot will put the bbls out commission.

If thin walls were a problem and minimum thicknesses needed to be established, the London & Birmingham proof houses would done it and they would fail any gun with walls below the minimum.

In the past they did not do this, and as far as I know they still don't.

OWD
Posted By: L. Brown Re: Minimum Wall Thickness Revisited - 12/15/11 01:34 PM
An article from the American Rifleman dated Sept 1931 shows a bunch of pressure barrels, all utilizing the crusher method, then in use by the major American arms and ammo makers. I don't know how accurate readings were farther down the barrel, but the article makes the following statement:

"These barrels are fitted with five or more additional pistons at intervals from the breech to the muzzle." The purpose was "for a better understanding of the rate of burning or characteristics of pressure curves." Pretty much the same method Bell and Armbrust used, except theirs employed electronic transducers, in Bell's "Finding Out For Myself" articles.

As for failing guns with thin walls, Vic Venters' current article on proof in Shooting Sportsman indicates the proofhouse does not do that, although the British "trade" still recommends MBWT of .020.
Posted By: eightbore Re: Minimum Wall Thickness Revisited - 12/15/11 04:38 PM
Read Bell if you want to know where the pressure is.
Posted By: 2-piper Re: Minimum Wall Thickness Revisited - 12/15/11 08:41 PM
Burrard gave much insight into this pressure bit. In fact he laid out a chart showing, using normal bbl construction & a normal load of the powder in then current use, just how far from the breech it would even be possible to burst a bbl, barring a metal flaw or an obstruction. A flaw can of course allow a bbl to open at less than normal pressures, though generally not with the violence of an obstruction. An obstruction due to the sudden checking of the charge moving down the bbl creates a very high localized pressure spot.

Beyond this a normal bbl, once the charge has moved a ways down the bbl, could actually hold the closed cell pressure if it could be just brought up to this level. This situation does not normally occur though as if the bbl is plugged the ugly affect of the obstruction rears its head & if the powder is spread down the bore it is extremely difficult to get ignition.

Botttom line though is that as long as the metal is sound & there is no obstruction in the bore, it is virtually impossible to burst a bbl very much ahead of the chamber. Technically though, all things considered, the juncture of the chamber with the forcing cone is the weakest point in a shotgun bbl. Fortunately though max pressure has already begun to subside when this point is reached, so it is normally of no consequence.
Posted By: Gregdownunder Re: Minimum Wall Thickness Revisited - 12/17/11 07:13 AM
Originally Posted By: 2-piper
Botttom line though is that as long as the metal is sound & there is no obstruction in the bore, it is virtually impossible to burst a bbl very much ahead of the chamber. Technically though, all things considered, the juncture of the chamber with the forcing cone is the weakest point in a shotgun bbl. Fortunately though max pressure has already begun to subside when this point is reached, so it is normally of no consequence.


Sums it up really .
Makes you wonder however why everyone is so precious about minimum wall thickness.
In reality the only issue I can see with thin barrels is the likelihood of damaging them.
As long as the chambers have not been lengthened and the chamber/forcing cone area is free from pitting what does it really matter if the bores have been honed out of proof?
We seldom talk of minimum chamber/end thickness,but would not that be more logical from a safety viewpoint?
Makes you wonder why guns are deemed out of proof with only 5 tho or so wall thickness removed.


GDU
Posted By: gunsaholic Re: Minimum Wall Thickness Revisited - 12/17/11 10:09 PM
Taken from Griffin & Howe

16. Barrel Wall Thickness - The thickness of the walls of a shotgun barrel. It is reasonable to assume that guns built by responsible manufacturers are safe to shoot, when new, with the loads for which they were intended. As the decades go by, however, as barrels are or buffed for rebluing and as occasional pits are honed out of the bores, steel is gradually removed from the barrels. The barrel walls, already built thin for lightness, become thinner still. At some point they become too thin for safety. It is important to know the barrel wall thickness of an old, well-used shotgun before shooting it. A rule of thumb states that the minimum barrel wall thickness should be .020" in a 12 gauge gun.
They should sell what they state. Wasn't it not so long ago a gentleman here bought a gun from them, had some work done and found out the barrels wall thickness was below above #16.
Posted By: gunsaholic Re: Minimum Wall Thickness Revisited - 12/17/11 11:57 PM
Originally Posted By: JDW
They should sell what they state. Wasn't it not so long ago a gentleman here bought a gun from them, had some work done and found out the barrels wall thickness was below above #16.


Yes, I believe so. I was just showing another example of what the opinion of "acceptable tolerance" is. Whether someone follows the accepted norm is another matter.
It has nothing to do with you and what you posted. I just saw the name in the heading. If that particular event did not happen, I would be ok with them. There are more stories out there of what we think are reputable dealers and find out they are not.

Sorry to put this on this thread as it is a very important subject.
Posted By: nialmac Re: Minimum Wall Thickness Revisited - 12/18/11 02:00 AM
Concerning G&H, a few months ago I posted about looking at a gun there and when I asked them to measure wall thickness it came to .014". I said too thin for me, they put it back in the rack. I like G&H. This isn't a judgment on their business practice, I expect all gun dealers would do the same. Let the buyer beware.
nial
Posted By: Small Bore Re: Minimum Wall Thickness Revisited - 12/18/11 01:26 PM
I just examined a Boss SLE at Holt's with a minimum wall thickness of 14 thou. It had a visible rivvel (not a ring bulge but a distortion of the metal) which I could see clearly at the thin spot, probably where a dent had been raised - the proof house inspector must have missed it. The gun had 2011 proof marks on it. It should not have passed proof. It needed sleeving or re-barreling.

The proof house has no interest in wall thickness. If the material is strong enough to withstand proof charges it can be one thou thick, it will pass - if it is not strong enough at 45 thou thick it will fail.

You cannot guess wall thickness by looking at the gun. You have to measure the walls carefully. It is very difficult to blow up a well made gun forward of the chambers just because the walls are thin. However, it is not uncommon for them to develop bulges and rivvels and dents as a result of their thinness. This is a concern as to value.

The Boss in question sold for £7,000 plus commission. With walls measuring 24 thou or more it was a good enough example to command a total price of over £20,000.

Buying a gun with thin but functionally adequate walls is a means of having and shooting a top quality gun for low quality money. A client of mine keeps a Lang Imperial sidelock here. He shoots it every time he visits from N.Z. It cost £3,000 because it has one wall down to 18 thou. With thicker walls it would be a £10,000 gun.

He made the informed choice that rather than a very solid but ordinary boxlock ejector with thick barrels, he wanted a best quality sidelock ejector for the same money to use when he visited the UK for driven and walked up game shooting. It works, it was a good choice and he paid the right money for it because he was in possession of all the facts when he made he purchase.

There is no 'right answer' on wall thickness, there are informed choices to be made and to make them one needs to in possession of all the data and have the knowledge and understanding of it to make them.
Diggory, very good explanation, but for you there, in order to sell a gun it has to pass proof. Here there is no such thing, and in my opinion if a seller sells a gun with known bores of .020 or less (seven sheets of standard printer paper), especially within the first 17" of breech, that is unjustifiable and shows he/they are only interested in the money and not your safe being.

Here we have a variety of people, and hopefully the ones buying these old vintage doubles have some common sense in the type of shells they use in them, but there are always some that don't.

The old saying Caveat Emptor should not apply to guns with less than minimum wall thickness, and sellers should realize this.

Just my opinion.
Posted By: Small Bore Re: Minimum Wall Thickness Revisited - 12/18/11 06:53 PM
The situation in the US is a little different as you say. The proof laws offer a little safety net and ensure new guns are fit for purpose before they can be sold.

Everything has avalue and it is legitimate to sell any old item. The key issue is disclosure for the responsible seller. The key issue is caveat emptor for the careful buyer.

For example, I will happily buy a thin gun for the right price - I may decide I can do well by sleeving it. If I do not realise it is thin and pay too much for it - then I would be foolish and fools and their money are soon parted.

As a responsible dealer, I would always provide all the data required and advise ignorant customers of the shortcomings of the guns in question, as reflected in their pricing, and try to fit the needs of each customer to the hardware available according to their means or willingness to pay. Not all dealers or private sellers can or will do this.

Therefore, the onus on the buyer is always to educate himself about the equipment he intends to buy (whatever it is) or enrol the help of someone who does to advise him.

I know a little about classic motorcycles but if I were about to spend £10,000 on a Brough Superior, I'd have a friend with me who renovates and races them to pick up all the important stuff I would miss.
Posted By: Gregdownunder Re: Minimum Wall Thickness Revisited - 12/18/11 07:02 PM
Out of interest,from 1891 so more than likely Damascus barrels?
Posted By: Drew Hause Re: Minimum Wall Thickness Revisited - 12/18/11 07:33 PM
No Greg; fluid steel barrels including Whitworth and Siemens were part of the 1891 Birmingham Proof House Trial
https://docs.google.com/Doc?id=dfg2hmx7_242cxhh9hfq
Posted By: Gregdownunder Re: Minimum Wall Thickness Revisited - 12/18/11 08:03 PM
Yes,I was just pointing out that these thicknesses would have been considered fairly normal for Damascus or steel barrels at the time?
I expect nowadays modern barrels would possibly be thinner at the breech due to stronger steels.
Posted By: Rookhawk Re: Minimum Wall Thickness Revisited - 12/18/11 08:39 PM
Greg, I've seen that photo before and I think it is of great help. Since it doesn't provide a measurement at 8", and since that is a common measurement area, would it be reasonable to estimate that it would be .070" at 9" from Breech? And .081 at 7.5" from the Breech? Thus, at 8.25" from Breech it would be
.075"? I could extrapolate what 8" would be with a spreadsheet ASSUMING that loss of metal to the walls is consistent in the gaps on the drawing above.

I've heard before that you want to be at .045" to .050" at 8" from the breech but I could never identify the reference that drew that conclusion, I merely am repeating folklore.

Above all, I want to:

A.) Be safe
B.) Buy safe, usable guns that may be overlooked as having too thin of a minimal wall, provided that it truly is a safe gun where the metal really counts. (e.g. more metal further towards the breech, why would I care if it is .020" in a cylinder bore 2" from the muzzle?)

The other question I have for the group is, does math help tell the story? What I mean by that is that I've heard some guns (e.g. old Boss) were made very thin from the onset. I have a Boss hammer gun with .025" minimum walls and the bore diameter is pretty close to .729, and it's marked as a 12 bore on its original proof. Wouldn't the math involved say that if it left the factory as a marginal bore diameter of .729 and therefore it is likely it was born fairly close to a .025 minimal wall thickness?

What is the most common bore diameter for a vintage English 12 bore (actual bore) that was proofed as .729/12 ? Would they have been likely to be about .725 on average at factory new? .720? Or .728"?

The reason I suppose this is important to know is in order to determine just how much of the bore has been removed from honing over a century of use and what was the likely reduction in metal over that period of time. If someone could provide a reasonable estimate of how these .729" guns were really bored, we'd probably be able to estimate how the wall thicknesses probably were originally too, compared to where they measure now.
Diggory, "As a responsible dealer, I would always provide all the data required and advise ignorant customers of the shortcomings of the guns in question, as reflected in their pricing, and try to fit the needs of each customer to the hardware available according to their means or willingness to pay. Not all dealers or private sellers can or will do this."

Well spoken. Also, some people that do not have the knowledge, depend on dealers or sellers to give me the correct information about a particular gun they might be interested in. This is especially true with Internet sales.

I would buy from you in a heartbeat, even before this posting, as you always have given very sound advice. But lately I have heard some nasty stories about some of the "big time" dealers that are well known on this site as not doing the same etiquette thing. If they puchased gun at a good price and knew about problems of barrel wall thickness, and now try to pass gun off at a far greater value, that is wrong.

Just a rant, and I guess it will always be so.
Posted By: Gregdownunder Re: Minimum Wall Thickness Revisited - 12/18/11 09:22 PM
As I understand it a bore proved and marked 12,as opposed to 12/1 or 13/1 would have taken a .729 plug and not a .740 plug when gauged.
Therefore actual bore diameter could be anything from .729 to .739 from new.
It seems very common for older black powder hammer guns to be proved as 13 or 13/1 bores.
I even had one that was a 14 bore .
As has been mentioned previously it is virtually impossible to burst a normal barrel much forward of the chamber from pressure alone.
In order to do that the pressure at the breech would have been such that it or the action would give way first.
However Burrard does point out that very thin barrels can give way from normal pressures but he was talking paper thin or heavily pitted in a concentrated area.
Interestingly he goes on to say such bursts are notable for their lack of violence,said barrels just peeling open.
Not that I would particularly want my hand there at the time,violent or not.
Personally I would quite happily shoot a sound barrel honed out of proof so long as the chamber was original and free from pitting and the wall thickness was fairly normal.
Besides this is all you can do with an American made gun is it not?
Posted By: Rookhawk Re: Minimum Wall Thickness Revisited - 12/18/11 09:27 PM
Originally Posted By: Gregdownunder
Besides this is all you can do with an American made gun is it not?


Forgive me, I was asking about English guns and English Proofs. I wouldn't know the first thing to do with an American gun. Not a fan. I guess that makes me one of those "self loathing Americans". smile
Posted By: Clif W. Re: Minimum Wall Thickness Revisited - 12/18/11 09:29 PM
Point of Proof is 9” from the breach, all other measuring points are less important. The thickness and bore dia at that point is what counts and tells you if you have a gun or not. Over worrying about thickness at the oft measured thin spot of 8" from MUZZLE is pointless except to foster sleepless nights worrying about denting it down the line. Of much more interest to me is the minimum acceptable wall thickness at Point of Proof
Posted By: Gregdownunder Re: Minimum Wall Thickness Revisited - 12/18/11 09:40 PM
Yes but we don't seem to have any standard minimum 9" from the breech.
I would prefer a standard minimum at the junction of the chamber/taper and/or 1 inch from the breech face as pressure falls away rapidly after this point.
I cannot help but wonder why the proof house is so hung up on bore diameter.
You are never going to blow up a barrel at the chamber because the bore has been honed out.
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