I need to make a couple of welds on a shotgun barrel for a project

Plz gunsmiths/welders, halp

>>31731254
Tig it, if only because it's cleaner.

I'd stress relieve it afterwards at least. What's the barrel made from? Do you know?

>>31731254
brazing is always recommended for barrels.

>>31731533
He might not know how to braze. Not something people really learn to do these days.

>>31731533
>>31731552
I will say that brazing would serve you better than welding, however - especially if you want to avoid fucking up the inside of the barrel if and when you overpenetrate the weld.

>>31731552
Really? I know Hartlöten from plumbers, joining copper pipes. They usually present this at job fairs, seems to be quite common here. Maybe not in the US?

>>31731647
>Copper pipe

PVC reins supreme here.

OP: As far as I'm aware, gun barrels aren't actually hardened or tempered - they're merely stress relieved after machining operations are completed.

>>31731676
But your gun barrels are still metal?

>>31731701
For now.

>>31731254
Welder/former pipefitter here.
Go low amperage, weld on opposing sides a little at a time (kinda like tightening lug nuts in a star pattern) and let the steel relax between welds. Id go two tacks on opposing sides, then wait, then two more tacks, then wait, then connect the tacks one bead at a time, waiting in between. Let the barrel air cool between, do not try to quench it, and you should be alright.

>>31731728
Also meant to ask, whats going on this collar? Its it going to see a lot of stress?

>>31731254
>Mig
>On a gun
>On a shotgun barrel
This is so bad of an idea I suggest you do it and post results.

But to answer your question. Firstly, don't do it. It's clear from the nature of your question that you are no experienced in welding. Buy a new barrel.

Secondly, yes you would need to reheat treat the affected area. However this is not a task for a novice. Do not attempt your own heat treat with a oxy-fuel torch and a color chart. It will end badly.

Dude, welding will absolutely ruin the temper on any steel I'm aware of and create weak points.

If it fractures its probably going to be on the weld.

However so long as you're not using extreme loads like hot as fuck hand loads you'll be fine most likely.

Retempering might relieve most the stress on the molecular level as other anons have said, but were you did the weld will likely always be where the weakest link in the steels crystalline structure is.


I'm not an expert at all BTW no sue pls

>>31731529
I do not know the exact steel unfortunately.

>>31731533
But brazing raises the temperature high enough to require re- heat-treat, too?

Also I have never brazed shit but I do weld.

>>31731745
It will be an anchor for a suppressor baffle stack.

>>31731808
I have some years on MIG and TIG, but I have never done serious work on barrels.

>>31731845
There's not temper on firearm barrels. Anything you did to it would be ruined the first time you mag dumped.

What you don't want is for the weld to harden it, because that'll make it crack.

>>31731937
>But brazing raises the temperature high enough to require re- heat-treat, too?

Depends on the filler you use.

Chief reason to use it rather than weld is the lack of penetration.

>>31731937
OP, whatever method you end up using, you're going to need to stress relieve it.

>>31731676
The bar stock that they're machined from are definitely heat treated. Just because they aren't heat treated after machining doesn't magically stop them from being heat treated.

>>31732108
Milspec AR barrels call for a hardness of 30 RC. I couldn't tell you off the top of my head what the hardness of 4130 stock is in its annealed form.

>>31732034
But I am worried that brazing wouldn't be strong enough here. The collar is holding a baffle stack and the primary expansion chamber in place, so it will be getting some violent forces affecting on it.

>>31732084
I suppose that is the case here, yeah.

>>31732011
>Anything you did to it would be ruined the first time you mag dumped.
How hot do you think the barrels get?

>>31732204
Around 18 Rc, though technically you should be using Rb or Hv, since HRc is not a reliable measurement below 20.

>>31732246
400 degrees if you really start to throw lead downrange.

Guess what the lowest tempering temperature of 4140 is?

>>31732273
We temper ours around 1300 to achieve 36 Rc, but obviously it depends on the application.

>>31732293
All depends on what end of the hard to flexible range you want the part.

>>31732273
>>31732293
And for the record, the SAE and AWS both call for a minimum pre-heat weld temperature of 900 for 4140 steel.

>>31732318
One more thing for OP to fuck up on. Do they even make hot plates big enough for that?

>>31732312
Well, I did say 36 Rc. That's not exceptionally hard or anything. If the barrel of a AR calls for 30 Rc (as someone claimed earlier) then you'd raise the temperature 120 degrees to 1420.

>>31732353
30-33 Rc is the accepted range for government contracts. I remember talking to a guy that worked for a company that supplied Colt with steel, and they wanted their's the same.

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>>31732338
>Using hot plates to temper

>>31732338
Any oxy-fuel torch with a neutral flame will work for preheating. If you have some Tempel sticks it'll take a lot of the guess work out.

But OP still shouldn't do it if he plans on using the barrel for shooting. If he's turning it into something like a leg for a stool or something that'd be fine.

>>31732374
No, to pre-heat the part for welding. It has to be 900F WHILE you're welding the thing.

And I said hot plate because that's a convenient option that welders often use for just such a task.

when you kill yourself OP have your family post the obit.

>>31732393
OP here.
Well fuck. How would you suggest I go about attaching the baffles to the barrel?

And just FYI I am planning on integrally suppressing my 20ga single-shot. I have buolt and designed suppressors before but this is my first integral one.

>>31732433
Just use a hose clip and really tighten it.

>>31732439
Nah senpai, I want to make it pretty n' shit.

>>31732474
Thread the tip of the barrel, like a normal person would.

>>31732507
But that isn't really an option with an integral suppressor if you want the back end to seal the gas.

Integral suppression is pretty much the only kind of suppression that makes sense with a shotgun.

OP: I think your best bet would be to teach yourself how to braze, and when you're ready for the real thing, use a bronze filler with a melting point of around 1375-1450F. That'd roughly match the temper you'd aim for in a 4140 barrel - although obviously you'll never get it perfect.

Just make sure you heat the whole thing evenly, and gradually. Once you're done, bury it somewhat deep in sand or lime and let it cool slowly.

>>31732433
Get a heavy rifled barrel, have a machinist thread the end of it, attach the baffles and solder them. Soldering should hold at hold and can look nice enough after being polished.

>>31732533
Why rifled? I'm going to be shooting mostly birdshot and other hunting loads.

>>31732629
It'll thicker, meaning it'll hold threads better and easier. You may be able to find a smoothbore that'll work, but I'm unaware of any.

>>31732629
I can't think of anyone that makes heavy profile smoothbore shotgun barrels.

>>31732729
>>31732756
Well cock.

I'll have to consult some britfag I guess, they make integrally suppressed shotguns all the time.

I actually bet welding it would be just fine, considering that even a shitty plumbing pipe can deal with a 12ga, but I like my eyes so better safe than sorry.