doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com Barrel thickness study

I happen to found a gunsmith who had a barrel thickness device, and asked him if he could measure my new gun, and he said NO, but you can take it home and do it yourself

I have a British made side by side shotgun in 16ga from 1910. Barrel is nitro proved.

With a white marking pencil, I made 1cm marks over the rib, from 1 to 71 cm. Using the tool, I placed the barrel on each mark, carefully moved from one extreme of the rib to the other extreme, and took notice of max and min measure I got. Made it with both barrels, then used excel to convert to mm if needed, and plot a simple column graph that shows the barrel contour....

First measure was made al 9cm from the breach, last one at around 65cm because of the choke.

What I noticed was that min reading, but not always in the same spot, but normally in the same area, and that there where 2 areas of max and 2 areas of min readings....That is: max reading, then a low reading, then a high reading, then a min reading... Strange... Of course thickness of the barrels were they are soldered, are not possible to read.

In summary I get the lowest readings at about 43-45cm from the breach, reading 0,027" (0,6858mm) at the left barrel and 0,030" (0,762mm) at the right barrel.

And the important readings at 9" from the breach, (23cm), was 0,061" (1,5494mm) at the left and 0,065" (1,651mm) at the right...

This process of reading nearly 250 measurements, took about 1 hour (now I understand why the gunsmith didn't want to do it jajaja), as you have to be extremely careful and move veeery slowly not to get errors, and frequently removing the barrel to see if the dial gets a cero reading again or it has moved.

Any comments or suggestions now that I still have the device, would be appreciated.

Paco

My heartfelt compliments as to your attention to detail and especially your endurance! You are an engineer?
There are wall thickness recommendations here, with a link to a previous thread on this forum
https://docs.google.com/document/d/1ZIo0y746UsSRZIgRuuxwAbZjSBHitO_EanvwLYc-kGA/edit?tab=t.0

I assume the gun was proved with 2 1/2" chambers, and the chambers have not been lengthened. The next time you tackle this ordeal, it is important to document the forward end of the chamber wall thickness also.

IMHO those numbers appear original and .027" left and .030" right at (about) 17 inches are not a concern, with shells generating pressures for which the gun was proved. The 9" numbers are a bit greater than are typically found on small bore game guns.
Under the 1896 Rules of Proof the 16 bore service charge was 1 oz. 2 3/4 Dram Eq. (1220 fps)
Pressures reported for bulk smokeless powder were “Schultze” - 8,250 psi & “E.C.” - 8,960 psi - both + 10-14% for modern transducer numbers.

Something to consider:

https://vicknairgunsmithing.blogspot.com/2020/03/mechanical-wall-thickness-gauges-are.html

BTW: I own and have used a Galazan style gauge.

OWD

and keeping it simple...

follow old ed's 90/30 guidelines for safe shooting...

minimum 90 thousands in front of chambers and 30 thousands seven inches down from muzzles...

and this ed's guidelines for fudge...

5 thousands for both...

use ammo that will not cycle a browning a5 set up for heavy loads...

Yes, Dewey he is true that ultrasonic measure is far better than any other method, not to mention no one has access to it.

In the real world, mechanical devices are used to measure, some with bad accuracy, some with good, and some with very good, depending on quality construction, but specially on the hands that use the device and the conditions.

I took the device on Sunday to a friend, is is a master mechanic, taking the responsibility of installing and certifying huge power pumps around the world for nuclear plants, and similar things. He has been in the desert at 50 degree, changing a 1 ton shaft from a water pump, verifying bearings, run outs, etc. He knows his business and nothing was done without his signature and personal measurement and check. Of course, millions of dollars are involved in those business.

He has also been gunsmith

He said the truth, the vertical device is not exact, but in the correct hands it is almost as perfect as we need. He also mentioned no measure is perfect unless perfect conditions are used, and if several measures are done, they must me done in exactly the same conditions. That is why in the desert, they always made measures exactly at the same time, for example at 6am, and not at 4pm after the sun has expanded all the metal.

Also he mentioned, that in the metrology/measurement world, ranges exist.

So yes, I already knew the measure I made might have a very slight variation, but it gives a very approximative photo of the condition of my barrel, and for me, that is better than nothing, more than just looking at a bulb and saying how shinny and correct the barrel is as many people do....

yawn...

I now use a Hosford barrel wall measuring device. Bit costly I admit and takes a bit of learning how to use it, but you get consistent results that so far I have found to be highly accurate. Your measurements look about normal from a profile of wall thickness and seem to have good remaining wall thickness.

For my part I measure looking for any areas below .025 and then zero on any near .020” as the bottom end of what I am comfortable shooting. That is a personal thing. And location is everything for thin areas. 20” down the barrel is fine but within 20” I take extra time evaluating them. Guns pass proof with sub .020 thickness and are deemed in proof. They are even shot with .015-.017” thickness without fail depending on location. I just decline to shoot them.

21 pages of erudite discussion regarding wall thickness measurement
https://www.doublegunshop.com/forums/ubbthreads.php?ubb=showflat&Number=615160