Welding 40mm US Gov't cannon barrels?

[cannonmn]

Friend wants to use arc welding to fabricate a BP cannon from an Army "Duster" 40mm cannon barrel section, made ca. 1950's, that we sold him sometime back.  He's asked my advice on whether the metal is weldable in air using ordinary welding rods and techniques. 
 
I don't know, the only barrel I welded on was a 6" section of a 105mm howitzer barrel, welded all around one end onto a steel plate, for use as an anvil launcher.  It failed massively after only a couple of shots, and I don't know if the problem there was the barrel metal or the plate we welded onto it.  I had no idea what alloy either piece was made of  so we knew that experiment might have been doomed from the start.

[moose53]

Easy enough to try . Just weld a test bar on the end you are going to try , and then knock it off . My guess is it will pull the whole weld out of the barrel . If it does ,it will do the same when you shoot it.

[bluez]

In my opinion the best way to this would be to make a 40mm steel that fits perfectly inside the barrel and goes 2-3" inside. He might need someone that has a lathe to make the plug for him. 

The best would be if he has to heat up the barrel and use use a hammer to get the plug in to the barrel.
(not to much force should be used, it can weaken the barrel (Yeld point) )

Then he should weld the plug to the barrel at the end. Now he has a very solid construction.

As an option he might also drill a hole from the side of the barrel through the plug and insert a hard steel bar through the hole.





 

[Zulu]

In my opinion the best way to this would be to make a 40mm steel that fits perfectly inside the barrel and goes 2-3" inside. He might need someone that has a lathe to make the plug for him. 

The best would be if he has to heat up the barrel and use use a hammer to get the plug in to the barrel.
(not to much force should be used, it can weaken the barrel (Yeld point) )

Then he should weld the plug to the barrel at the end. Now he has a very solid construction.

As an option he might also drill a hole from the side of the barrel through the plug and insert a hard steel bar through the hole.

I have to suspect that the barrel is rifled.  Hammering a round plug into a rifled barrel can't be good.
Zulu

[dominick]

The method I would use would be to cut a small sliver and send to to a metallurgy lab and have them perform a "numerical designation by composition test".  This will tell if the steel is weldable and if so, what rods to use.  There's a lab in Lancaster, PA and the cost [I think] is still under $100.  Henry J. Yeager laboratories.
  Some steel cannot be welded correctly at all for barrel use.  A preliminary test prior to sending a piece to the lab would be to cut a cut a sliver 1/4" thick and weld it to a thick plate with 7018 rod.  Let cool and bend it over with a hammer.  If it breaks very easy at the weld, then it's possibly non weldable. If it folds over flat against the plate without bending or cracking, [which I doubt a rifled barrel will do] then it's a soft, low carbon steel.

[cannonmn]

Thanks for the info, I'll send it along to him, plus any other credible info that shows up here.

[KABAR2]

John, when you welded the plate to the section of 105 barrel were both pieces heated and welded or were they welded cold? This can make a big differece in how well the weld takes between the two metals......

[cannonmn]

Nothing was heated prior to welding that time.

[GGaskill]

I would send him to your junk yard friend with the X ray fluorescence tester and see if he can determine the alloy.  The basic problem is any hardenable steel will develop brittle spots or cracks if the welding is not done at an elevated temperature.  Even then, some alloys are unsuitable for welding and should use a screw in breech plug instead.

[cannonmn]

junk yard friend with the X ray fluorescence tester

Sounds reasonable if the alloy can be determined using the limited number of elements that device can detect.  One it can't see is carbon, unfortunately.
 
I looked around and found some sizeable, but mostly useless pieces of those barrels we'd cut up. in the past, so maybe we'll just try welding it to something. 
 
That is, after my elecronic welding mask comes back from the repair shop.  The batteries that make the lens darken automatically were soldered right onto the circuit, so they aren't easily customer-replaceable.  An electronics repair place near my business said they'd do it for $20.  I think my friend is going to send a sample to the lab mentioned above also.

[KABAR2]

I am interested to hear the results if he is willing to share....
He's not the only one with a 40mm barrel section....

[Double D]

Last year when Dom and I went to the scrap yard, they had a handheld tester that told us the piece  steel we were looking at was 4140.

Most likely that is what the 40 mm barrel is made from, some sort of steel similar to 4140.  High carbon content requires special preheat welding techniques.  One industry that use a lot of this type of steel is the Oil patch.  Those folks will know how to do a proper weld of high carbon steel.   

[michaelfreeland]

I'm in the middle of a 40MM build right now, and am wondering why you need to weld anything. I'm assuming you want to make a chamber at the end of the cut section you have. Look at Moose53's work; how about a fine threaded insert, set in place with green loctite? you can even put the cascabel shape right on it.
I'm guessing this can be done in about a day or less by a good lathe hand, If you don't have one, PM me and I can get you set up.

[cannonmn]

and am wondering why you need to weld anything.

Let me clarify.  We sold a barrel to a customer who is now asking us if the barrel can be welded or not.  We're trying to help him get an answer to that question as a "customer support" action and that's all.   We wouldn't want to tell him how to (or how not to) make a cannon; all we do is sell stuff. 

[Double D]

John, the safest answer is that without knowing the specific alloy used to construct the barrels, these type of barrels should generally be considered not weldable.

[dominick]

The test I mentioned above will give him the 4 digit AISI number of the steel alloy that the barrel is made of.  The AISI number will indicate the point percentage of carbon in the steel along with the alloying elements.  Many folks here know that this number is what we often discuss in cannon construction. ie, 1018, 1026, 12L14, 4140 etc.  I do not trust the X-ray tester as it has given erroneous readings in the past.

[cannonmn]

Thanks, customer now has all all the info, will post anything I learn from him after he's digested and/or acted on the info.
 
For Dom:  Art visited my vendor space here in KY today.  The folks who run a booth he visited today were having a hard time finding cannon grade BP so I suggested one in Gainesboro, VA.

[dominick]

For Dom:  Art visited my vendor space here in KY today.  The folks who run a booth he visited today were having a hard time finding cannon grade BP so I suggested one in Gainesboro, VA.

Cool, tell him to sell, sell, sell!      I wonder if powder inc. is out of cannon grade.