Silver soldering?

[Aguila Blanca]

What is it -- exactly -- and how is it done?

I'm playing with the notion of adapting a semi-auto handgun to a different cartridge of the same caliber. The barrel bore and groove diameters are the same for both, so what I would need to do is to bore out the chamber area slightly and machine an insert that's machined to the proper dimensions for the new cartridge.

Machining I understand -- although I don't currently own a lathe, so I would have to farm out the production of the insert, and the boring of the chamber in the original barrel. If I can get that taken care of, then the issue is how to secure the insert into the barrel.

Would a interference for be sufficient? This would mean freezing the insert and heating the barrel (to what temperature?) so that, when both parts normalize to the same temperature, the insert might be tight enough to function.

Or not. So then I think silver solder is the next option. I believe that's how two-piece barrels for pistols like the 1911 are made, and it mostly works. (I have seen photos of Springfield Armory two-piece barrels that self-disassembled.)

Is silver soldering really "soldering" (like, could I just use the non-toxic solder from Lowe's or Home Despot?) or is it "brazing"? If non-toxic plumber's solder isn't the right material, what is? And how hot does it have to get? Can a gun barrel be silver soldered without damaging the heat treating of the barrel?

TIA

 

[Bill DeShivs]

True silver soldering is actually silver brazing, and requires temperatures in the 1000+ degree range.

The "silver solder" you see at most big-box hardware stores is "silver-bearing" solder. It is stronger than lead solders and the small amount of silver (4%) allows it to be used on stainless steels. Temperatures required are around 400 degrees.

If there is enough room, you might thread the parts.

 

[Jim Watson]

Caution: Like Will Rogers, all I know is what I read on the internet. And some old books.

Silver soldering is brazing, melting point of high-silver mix is 1100 F or thereabouts.

Maj. Geo. C. Nonte wrote of lining pistol barrels with low-silver solder at 450F and "pressing in" chamber bushings, which might say the hot/cold interference method would work.
Parkerifling was done with lead solder.
Lots of liners are glued in these days with epoxy or Loctite. I don't know how that would translate to a chamber bushing.

What calibers/pressures?

 

[HiBC]

You might get some grid paper and make a 10X drawing (or use a CAD software like SolidWorks)

Get a layout and figure how much steel you will have at the stressed corner of your insert counterbore. Consider where your locking lugs are and the "root" that gives your locking lugs strength.

There is more structure to look it than just anchoring a chamber sleeve.

There are different grades of silver solder. Brownells Hi-Force 44 on the low end flows at 400 something deg F. And they have a stronger 800 deg F grade. Sometime in the 1980's I cut my Super Blackhawk to 5 in and soldered the front sight base back on with Hi-Force . There is a pin there to take shear load. Its still on the barrel. The flux ran when heated and stripped the blue off.

Silver Solder require some clearance to flow and fill the gap,making the bond. Ballpark .003. Its a bit like sweat soldering copper pipe. When it flows...it tends to wet out,maybe where you don't want it to be. If you are skilled enough to get a fully filled 100% joint without getting your bore throat covered with silver solder,I'd be very impressed. I'm not that good.

I was fitting some Numrich 20 ga barrel blank to an Ithaca 37. I needed to silver solder the lug to the barrel the mag tube cap engages. This was a hard,strong,higher temp solder. More than 1200 deg. Maybe approaching 1400. There was stress in the steel and expansion. A goose egg grew on the barrel where I heated it and the barrel was not straight any more. It was not particularly a success.

Generally.....my guess? You have a very high probability of investing time,money and a barrel into a "Fail" project. I won't say "Can't..." but I would not bet on success.

But,say you get it done. I'm impressed! Will it proof test? If it fails...it might get expensive. Doctors don't work cheap.

We don;t know what your cartridge is, but if you explore the BarSto or Kart etc pages you might find an unchambered barrel in the bore size you need.

Actually,SARCO just got in a whole heap of various barrel blanks of every kind from somewhere.

If you want to see something interesting, go to Varmint Al's web page. Look for his images of Finite Element Analysis. For example,he has one where you get to see how stress travels through the steel of a Rem 700 receiver.
Enlightening!

 

[Scorch]

I believe that's how two-piece barrels for pistols like the 1911 are made

Real 1911s don't have 2-piece barrels. Clones of 1911s and cheap import 1911s may have 2-piece barrels, but the M1911 is a "standard" and all the parts are specified as to construction. Cheap copies are not really 1911s, they are 1911-ish. Rant over.

So okay, I have done what you are talking about with a St Etienne 1935A in 32 French Long, converting it to 32ACP (had to modify the slide as well since they don't have the same rim size). Yes, you can do it either way, shrink fit or solder a ring in place. If you opt for solder, use low-temp solder as per Bill DeShivs advice. Or line the chamber, leaving a headspacing ring in the new chamber.

 

[FITASC]

I can say that some of the shotgun makers are now using some type of adhesive to glue barrels into the monoblock; it is supposed to be as strong as silver soldering but without the heat stress and potential warping. (I believe it is more for its cost-cutting properties though)

 

[Unclenick]

Brownells thinks Loctite 380 (Black Max) can handle keeping shotgun sights and ribs in place, but for chamber insert glue I would look at one of the high temperature ceramic adhesives. Look at Resbond 906 at Final-materials.com. It will handle 1650C (3000F) and is specifically for bonding to metals that include Stainless Steel and other high temperature coefficient of expansion materials. I don't have any, so it is just a suggestion for something to look into that won't be softened by chamber heat. I would talk to an application engineer to be sure it will handle the shock of firing expansion.

 

[Nathan]

Let’s start at the beginning….what is the purpose of the insert, if bore and groove are the same?

 

[Unclenick]

He needs a different chamber, and the original cannot be modified to match what he needs. It'll be along the lines of rechambering a 9 mm Parabellum to 9 mm Kurtz (.380 Auto) or something analogous to that, where metal has to be added rather than removed.

 

[Nathan]

Well, that is kind of what I was worried about. I would have a real problem(from an engineering perspective) with the idea of putting a thin wall insert into a chamber. A chamber is a pressure vessel. The insert needs to be treated as a separate part. Which means it must hold the pressure with the appropriate factor of safety…which is quite large for human use and risk of death or dismemberment as a potential failure outcome. Will it be thick enough to withstand the full pressure load on its own? If not, short of doing some kind of TIG wire chamber fill and rechamber job. I’m not sure how to make it homogeneous enough. That is the key. Welding and recutting a chambe is also a bad idea in a world where barrel blanks are reasonably accessible.

If you want an expert to speak to, I would get a hold of Chuck Rodgers. He has done some serious 1911 repair by silver soldering in a block of steel and recutting.
Example of his work.