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Joined: Nov 2018
Posts: 100 Likes: 8
Sidelock
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Sidelock
Joined: Nov 2018
Posts: 100 Likes: 8 |
I make my own wall thickness gage similar to the one Drew has in his post. I have verified its reading via other methods such as cross sectioning ultra sonic and eddy current. They all give the same reading within .0006" which wouldn't make the slightest difference.
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1 member likes this:
Drew Hause |
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Joined: Mar 2002
Posts: 7,798 Likes: 566
Sidelock
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Sidelock
Joined: Mar 2002
Posts: 7,798 Likes: 566 |
What is really important? Accuracy and repeatability. If you get the "right" number, then it does not matter. Being able to check and verify that number over and over again gives you a bit of confidence. I have been using my setup for 20 plus years and checked it against known samples hundreds of times. When ever I find a thin area, I get real careful, but when going over a set of barrels, as long as the thickness is measuring above .025- .030 and is the same as areas nearby, I do not worry too much. If I find a area which is thinner than areas nearby, then I start looking for dent repairs and think about file work to blend the repair. If my setup is off .001-.005 I do not care as long as the walls are .025-.030+. I shoot several guns with barrels .020 as longs as the thin area is well towards the muzzle. But is is location and repeatability which my setup gives me consistently which is what I need. I know it is accurate because I have used it for decades and verified it with multiple other systems. We can not all be off the exact same way and same amount. Potential minor variations are not critical when you are talking about barrels not near a critical thinness. Mine are not. If I got to the point that .0006 was important then I would find a new gun.
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Joined: Jan 2002
Posts: 536 Likes: 70
Sidelock
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Sidelock
Joined: Jan 2002
Posts: 536 Likes: 70 |
The question about wall thickness just in front of the chamber was important to me, as I have a couple great old guns that have been lengthened from 2 1/2" to 2 3/4" chamber without reproofing. One was done by a very reputable gunsmith operation and they assured me it was safe to use. Both are over .100 right in front of chamber. I was doing research and found in one of Gough Thomas's books where he measured pre war English doubles and post war Italian, Spanish and Japanese guns. The English were from .106 to .122 with several in the .113 range. The post war doubles were .076 to .086. He also discusses elastic limits and a safety factor of 2, states a gun with working pressure of 3 tons should be .084.
This ain't a dress rehearsal , Don't Let the Old Man IN
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Joined: Oct 2006
Posts: 2,295 Likes: 564
Sidelock
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Sidelock
Joined: Oct 2006
Posts: 2,295 Likes: 564 |
I always use my gauges vertically. I have both the Manson style mounted to a wall and also have the British style wall thickness gauge, the type you’d find in most British & continental gunmakers shops. I much prefer the latter. My mitutoyo dial indicator is as good as it gets, and the readings when using that very rigid British style gauge are dead accurate and repeatable. If the gauge your using works correctly and you’re getting accurate readings, it doesn’t matter what type it is. I much prefer the British style gauge over the Manson though, but that’s just me.
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Joined: Jan 2006
Posts: 9,518 Likes: 352
Sidelock
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OP
Sidelock
Joined: Jan 2006
Posts: 9,518 Likes: 352 |
Thanks for that data Nitrah. The difference in Thomas' MWT recommendation is very likely related to barrel composition, and possibly service load pressure standards at the time of proof. Turn-of-the-century pattern welded vs. decarbonized vs. pre-WWI Siemens-Martin 1030 vs. 1940s 4140 matters.
In 1925, the British 2 1/2” & 2 5/8” 12g maximum service load was reduced from 1 1/4 oz. 3 1/4 Dr.Eq. to 3 Dr. Eq. with 1 1/8 oz. shot with a mean pressure of 3 1/4 tons by LUP = 9,800 psi by Burrard’s conversion. The 2 3/4” 12g max. service load was then 3 3/8 Dr. Eq. with 1 1/4 oz. shot with a mean pressure of 3 1/2 tons = 10,640 psi by Burrard’s conversion. (Primarily for heavier “Waterfowl” guns)
And that is why it is difficult to provide generalized wall thickness recommendations.
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Joined: Jan 2002
Posts: 9,804 Likes: 101
Sidelock
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Sidelock
Joined: Jan 2002
Posts: 9,804 Likes: 101 |
blah, blah blah....
it is all meaningless, unless you establish some minimum standards for operator safety...
my standard is .090 in front of the chambers and .030, 7" down from the muzzles...
what are your standards?
sorry, for loosing patience, but you guys dance around this like a bunch of fairies...
keep it simple and keep it safe...
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1 member likes this:
keith |
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Joined: May 2022
Posts: 24 Likes: 10
Boxlock
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Boxlock
Joined: May 2022
Posts: 24 Likes: 10 |
Slightly OT, but not worth a stand alone thread....
What are the nominal wall thicknesses for a 10ga? I see lots of info for 12ga, but not much for 10. I’d imagine the pressures (all things equal and applying common sense to loads) would be slightly less.
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Joined: Jan 2006
Posts: 9,518 Likes: 352
Sidelock
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OP
Sidelock
Joined: Jan 2006
Posts: 9,518 Likes: 352 |
I've only seen one period 10g pressure report; from DuPont Brandywine Experimental Station data cited by Charles Askins in 1933 DuPont Bulk Smokeless Powder (not Oval used for the Super-X loads). 10g 4 1/4 Dr. Eq. 1 3/8 oz. shot = 10,662 psi + 10-14% for modern piezo transducer numbers
And have a single 10g measurement; a Smith hammer gun with Twist barrels Bore .798" End of chamber L .174" and R .167" 9" from breech L .095" and R .092" 9" from muzzle L .052" and R .050"
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Joined: May 2022
Posts: 24 Likes: 10
Boxlock
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Boxlock
Joined: May 2022
Posts: 24 Likes: 10 |
Thanks much. I appreciate the response and info.
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Joined: Mar 2002
Posts: 2,857 Likes: 384
Sidelock
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Sidelock
Joined: Mar 2002
Posts: 2,857 Likes: 384 |
Mr eightbore,,,i think it's a Manson I always check vertically , the mwt could depend on the steel I have some krupp barrels that are .80 in front of the chamber and 30 9 inches from the muzzle I have some old heavy barrels that are much thicker
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