Gunsmithing Need to silver solder a mount to a reciever

[Flint62a1]

I have a mosin nagant sniper rifle. The smith who mounted it left me with a problem. A) theres a gap between mount and reciever. B) the screws (circled) keep loosening no matter what I try. I was thinking why not try silver soldering the mount like the Germans did with their mounts and scope tubes.
I am aretired welder with experience in gas welding, but I never tried silver solder. Has anyone tried this, any advice would be greatly appreciated
Kevin

 

[RTH1800]

Suggest you consider locktight and or a bonding compound like titanium Devcon to avoid heat issues.

 

[XLR308]

I was going to suggest marine-tex but that's pretty much the same outcome as rth1800 suggested.
I just switched to marine-tex a few years ago after my second batch of Devcon went bad long before I used it all and it's less expensive.

 

[sirhrmechanic]

I do a lot of silver soldering, but am a lousy welder. Adequate at silver soldering. Though generally small parts.

Very hard to control the heat to melt the solder and not over-heat the mount. Also, you have to do a bunch of prep to both parts to remove any finish/oxides, etc.

If you are a welder, have you considered spot welding the mount in place? Then you could fill the gaps with soft solder (which has a tons per square inch holding power by itself). Large items and silver solder are rough! Little things like sight ramps, etc. are not so hard. But big things... really take some skill.

There are also 'sheets' of silver solder that are designed for oven use. You clamp the sheet in between the parts and then oven braze/solder it.

If you are good at welding... I'd go with spot welding an soft solder. Or pay someone who does a LOT of silver solder to do it. It won't cost a lot. And they will know just how to braze/silver it.

Sirhr

 

[Flint62a1]

I was considering using an epoxy- jb devcon etc, to fill the gap between mount amd reciever. Then using same epoxy to seat the screws also?
the gap is slight but I believe under recoil it creates just enough movement to loosen the screws, over time. The screws are already loktited in, and its not holding.
If the epoxy filler can stop that movement I think that might solve the problem??

 

[ButterBean556]

I do a lot of silver soldering, but am a lousy welder. Adequate at silver soldering. Though generally small parts.

Very hard to control the heat to melt the solder and not over-heat the mount. Also, you have to do a bunch of prep to both parts to remove any finish/oxides, etc.

If you are a welder, have you considered spot welding the mount in place? Then you could fill the gaps with soft solder (which has a tons per square inch holding power by itself). Large items and silver solder are rough! Little things like sight ramps, etc. are not so hard. But big things... really take some skill.

There are also 'sheets' of silver solder that are designed for oven use. You clamp the sheet in between the parts and then oven braze/solder it.

If you are good at welding... I'd go with spot welding an soft solder. Or pay someone who does silver solder a LOT to do it.

Sirhr

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
X-2

 

[sirhrmechanic]

I was considering using an epoxy- jb devcon etc, to fill the gap between mount amd reciever. Then using same epoxy to seat the screws also?
the gap is slight but I believe under recoil it creates just enough movement to loosen the screws, over time. The screws are already loktited in, and its not holding.
If the epoxy filler can stop that movement I think that might solve the problem??

An anaerobic (epoxy) can be a good idea. Though there are some industrial epoxies much better than JB weld. 3M makes a material that is fantastic. I don't know if you can buy in small quantities. But it's used to put the wings on fighter planes and the roofs/tops on a lot of modern cars in lieu of welding.

ScotchWeld, I think it's called.

So if you think you can do it with an anaerobic... by all means, start there!

SIrhr

 

[kl3309]

Did your smith dimple the receiver under the mount for the screws? Could add an extra engagement surface with the epoxy.

 

[Flint62a1]

I dont think he did. The original mounting was a disaster that’s why all this. I’m going to remove the finish under the mount and on top of the reciever then dimple it or scratch it up to get a little more grip.

 

[jetmd]

My 3 suggestions:

1) Use the following as a bonding adjent:

3M Scotch-Weld 08966 Epoxy Adhesive DP420 50mL, DP420, Black: Amazon.com: Industrial & Scientific

3M Scotch-Weld 08966 Epoxy Adhesive DP420 50mL, DP420, Black: Amazon.com: Industrial & Scientific

www.amazon.com

2) If possible switch the screws out to a Torx head or recessed Allen head which allows the fastener to by tightened with a torque wrench to the correct
specification for that Diameter and Thread pitch.

3) Continue the use of the correct Loctite for this fastener.

JHMO

Respectfully submitted,

Chet

 

[Flint62a1]

The screws are 5mx.5 and they are all blind holes.
I have some Pro-bed here so I’m going to try shimming the mount with it in am effort to stop the movement. In the meantime I think I’m going to work on my soldering skills just in case
Thanks all, for the help.
Kevin

 

[Hobo Hilton]

It's all about the proper flux and getting the metal totally clean... Get those two things accomplished and a trained monkey can make the joint up.

Hobo

 

[Flint62a1]

I thought I would post a follow up on this rifle. After thinking it over (procrastinating) I decided to try the epoxy route. I cleaned up the action and mount, then got busy with the screw holes. When they were cleaned out of all the old loktite I mixed up some pro-bed and laid it on. Got plenty in the screw holes and locked it down.
Several hundred rounds later amd the fix seems to be working, it’s holding tight.

 

[Wannashootit]

That was the correct fix. Silver solder would have been a bad idea.
Had you silver soldered, you'd have destroyed the heat treat in the front of the receiver.

All of this is right in the area of the lug abutments.

It would have softened the abutments and they would begin to set back rapidly as you shot the rifle, eventually creating excessive/dangerous headspace and possibly even a catastrophic failure at some point where you'd end up with a bolt through your forehead.

The M39's have their rear sight right at the receiver ring (I've removed many of them)- while the Finns did use solder, if it had silver in it- it was low percentage as the melting point isn't anything close to high content silver solder we use.

 

[Flint62a1]

That was the correct fix. Silver solder would have been a bad idea.
Had you silver soldered, you'd have destroyed the heat treat in the front of the receiver.

All of this is right in the area of the lug abutments.

It would have softened the abutments and they would begin to set back rapidly as you shot the rifle, eventually creating excessive/dangerous headspace and possibly even a catastrophic failure at some point where you'd end up with a bolt through your forehead.

The M39's have their rear sight right at the receiver ring (I've removed many of them)- while the Finns did use solder, if it had silver in it- it was low percentage as the melting point isn't anything close to high content silver solder we use.

Thanks for the advice! I wasn’t really crazy about silver soldering, because of the heat factor. So far this epoxy is working. The whole issue with the mount was the gap between mount and reciever. That has been dealt with- hopefully for good
Thanks
Kevin

 

[strikeeagle1]

FYI- this product is good at mitigating undesired heat transfer to adjacent parts.