doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com Wall thickness recommendations

I am sure this has been hashed over here many times so if someone can point me to the correct thread that would be great. I have my new wall thickness gauge set up and mounted and can get some pretty good, repeatable readings. Now I just need to know where the readings should be at various locations in the barrel for safe operation. I will be testing 12 gauge barrels to start with and then a 16 gauge. There are no pits in any of the barrels so I am looking for thin areas. Thanks.

Tom,
Good afternoon.
No pics??????

Best,
Bill

Tom, I'm afraid there is no such data though some have created their own "minimums". I guess the main thing to know is whether the bores and chambers are original, discover any hidden repairs that may have thinned the tubes, etc. and if applicable, is the gun still in proof? There are just way too many variables to give any data points due to the differences in steel and damascus, intended use, etc.

Tom,
Thin is when it gets below .022" anywhere except choke area close to muzzle. From about 12" from breach back, WT should gradually increase. That said things like barrel steel and manufacturer matter as well. You are correct about this topics coverage many times past. I can't help locate those threads.
Bob J

Wall thickness as it should be. Anything less has been altered.




Published Data as a guide for Gauge Chamber End Diameter Minimum Wall Thickness reference:

12 0.800 0.085
16 0.732 0.075
20 0.610 0.070

More good info from Dr Drew.

Actual tensile strength testing of Twist and Crolle Damascus barrels show an average of 54,000 psi, or about half of the published industrial standard for AISI 4140 Chrome Moly gun barrel steel.

For that reason I favor as MWT for pattern welded barrels:
End of chamber - .105"
Forcing cone - .100"
9" from breech - .040"
9" from muzzle - .025"

Factory original 20 and 16 gauge small frame guns with Damascus barrels however may have a wall thickness of .090� at the end of the chamber, and .020� in the distal third of the barrel, making it critical to use loads that match the ballistics of those originally intended for use in the gun.

Its all well and good talking about wall thickness but without considering the particular steel the barrel is made you can give a false idea as to the guns shoot ability .e.g.. It was a held belief in the Birmingham trade that Greener's steel needed to be thicker that that of a Webley to achieve the same strength .Generally the biggest problem with barrels when the get below.025"is removal of dents as there is less metal to work with .

Many light weight Fox guns were made with walls well below the .035" you stated for unaltered barrels. You'll want to measure some Fox and others to see for yourself, if you own a wall gauge.

Doug! The illustration you provided is nothing more than the dimensions agreed upon to perform the gun trials carried on by the Birmingham Proof House as reported in "The Field" in March of 1891. All 39 different groups of barrels submitted for the test were turned to the same dimensions. It has nothing to do with what was considered to be safe dimensions for all sporting barrels. However, the illustration does provide a good visual of the general profile of a breechloading shotgun barrel. If these dimensions had been adhered to by British makers there would be very few of those superbly balanced lightweight game guns.

Joe is correct. The illustration in no way represents wall thickness recommendations
https://docs.google.com/a/damascusknowle...TEK8OtPYVA/edit

Commission Internationale Permanente pour l'Epreuve des Armes � Feu Portatives (C.I.P) http://www.cip-bobp.org/
Standard CIP proof pressure of 850 kg per sq. cm. (BAR) = 13,920 psi proof pressure = 10,730 psi service pressure (SAAMI)
Shotgun recommended minimum wall thickness (p.4) for Standard Steel with tensile strength 700 - 849 N/sq. mm = 101,526-123,137 psi
http://www.cip-bobp.org/sites/default/files/new_file/A-4-1_EN.pdf
PLEASE NOTE: actual tensile strength testing on a sample of pattern welded tubes averaged about 54,000 psi

For 12g Standard Steel.................................................20g
End of chamber - .079�..................................................075�
Just past the forcing cone/ 4� from breech - .075�................071�
8� - .043�..................................................................041�
12� - .030�.................................................................028�
16� - .024�.................................................................022�
20� - .022�.................................................................020�


More information, and opinions, which are all any of us can offer
https://docs.google.com/a/damascusknowle...nvwLYc-kGA/edit

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