How to Protect Bore When Silver Soldering?

[rhmc24]

Silver soldering (or brazing) a front sight on needs red heat which can damage the bore. What is the best protection from this? I used the old sperm oil and lampblack paste method that wasn't good enough.

[haggis]

Jam some plastic tubing of the proper size into the forcing cone end of the barrel, and trickle water through it and out the muzzle into a container (5 gallon bucket works). Use just enough water flow that the exit water starts to steam - you don't want to cool the soldered area too much.

Buck

[Oyeboten]

Hi rhmc24,


How would Silver Soldering on a Front Sight damage the Bore?

Oxidation?

If that is the concern, just melt Brazing Flux inside the Bore as things come up to heat, and, that would take care of that.


Haggis - Water trickling through the Bore would not work since it would flash to Steam at that heat, and or if it did not, it would cool things to where one would not be able to Silver Solder/Braze the new Sight on.

[rhmc24]

I guess it's oxidation, looks like rust. I scrubbed the bore good after and the lands came clean but left the grooves dark. After about 50 rounds of hardball it's looking pretty good - need to shoot more. The brazing flux sounds promising. I need to pore over all the old gunsmithing stuff I have & maybe learn more. This is the item at issue:

[Oyeboten]

I would expect Brazing FLux to work well to protect any close-by areas which one wishes to remain free of Oxides forming from the heat of Brazing.

[msheak]

A heat sink can be made . I have used pieces of aluminum rod of the proper size to fit the bore. Also heat paste around the area you are working.

[ShootingMaster]

Heating up a barrel shouldn´t be related only with oxidation issues but with metalurgical changes in steel microstructure as well.

I don´t know wich type of heat treatment, steel composition or steel microstructure is expected to find in a barrel (BTW it should be interesting to know this).

However if the barrel is heated up enough (roughly at 1000 F or more) some metallurgical transformation of the steel micro structure should be expected to take place.
Depending on maximum temperatures reached and cooling rates applied (after the welding process) changes in steel microstructure may possibly lead to different types of steel microstructure in the barrel thus resulting in a harder or softer steel condition that may differ from the original one.

So be careful when heating up a barrel. Try to cool it down as much as possible and to apply just the minimum amount of heat neccesary to do the job.

Regards.-

[BobSm]

Brownell's Heat Stop Paste was made specifically for keeping heat from where you don't want it. Swab it liberally in the bore before brazing.



HEAT STOP™ HEAT CONTROL PASTE - Brownells

But why you need a 40,000psi silver braze job on a front sight escapes me entirely. Brownell's Hi-Force 44, a 4% silver-tin solder runs 28,000 psi and is more than strong enough for a typical Colt blade front sight housed in a mortise or staked. 475 degrees and zero risk. Stronger isn't necessarily better.

HI-FORCE 44™ SOLDER - Brownells

PS. Also insure you buy and use a talc stick to coat all surfaces where you don't want solder or braze. There are several formulations of silver braze... some run and some don't...and the talc stick will save you a lot of cleanup if it runs.

[rhmc24]

I was hoping someone would come back with some old-time product, but thanks for the Brownells item. I imagine few people know about the soapstone stick as anti-flux. I have used high low-temp silver solder and don't share your faith in the low-temp strength. In my case above, it is a sight a little thicker than 1/16" that I attached. In another, the base about 3/16" wide, I used the low-temp attaching it to a filed-flat on the barrel.