Does anyone know if there is a video anywhere on how to silver braze a flash hider on a muzzle? As I understand it this is a legal perminate way to attach a muzzle device to a 14.5" barrel to make it 16". Also is a propane torch hot enough? Would a hardware store likely have the flux and filler I would need? Also what kind of silver brazing alloy would be most applicable to this application?

You'll probably need MAPP gas to get the barrel end and muzzle device hot enough for the silver solder to flow.

I and most persons I know who do silver solder for muzzle devices use a paste that contains the silver bearing solder and flux together. You can buy it plenty of places, like brownells.

http://www.brownells.com/gunsmith-tools-supplies/general-gunsmith-tools/solders-flux/dmx-1260-750-non-flowing-silver-braze-prod81391.aspx

Make sure you get high temp (1100F or hotter) silver solder to meet the requirements for permanent attachment.

Needs to be 1100 degrees or higher to be legal. I would get it in a paste form with the flux mixed in, either from Brownells or some other supplier. I can almost guarantee you won't find it at some hardware store. Propane probably wont cut it by itself. I used MAPP  before I got my Smith Little Torch.

Here's the solder that I used before I started blind pin and welding:

http://www.brownells.com/gunsmith-tools-supplies/general-gunsmith-tools/solders-flux/homogenized-solder-prod645.aspx

Many of the brazing rods used for refrigeration work are adequate.
Steel is a bit of a PITA compared to copper though.

Even a 'self fluxing' grade of refrigeration rod (they have about 5% phosphorous added) will need additional flux for steel.

Pay attention to the temp required.
It goes a lot easier with oxyacetylene.

Make sure you understand how to create a neutral flame.

And use enough torch [larger tip] to get in and out without overheating things.

This is what you seek...

The paste makes a mess.  Flux the inside of the flash suppressor making sure to have just a little on the outside.  Heat with MAPP gas torch, get it good and hot, then touch the silver solder to the joint.  The flux will draw the solder in.  You don't need a ton of the stuff, a little will do ya just fine.

Test it with a wrench when you are done.  If it spins off, you failed.  

Nothing like buying a "silver soldered" 14.5" upper from an arfcommer, only to find out the FH was less secure than with loctite.  I do actually gas weld, braze, silver solder, Mig, etc.. Once I sweated 150 copper pipe joints in a complicated shower install without a single leak.  No way I would braze or silver solder a muzzle device.  Propane probably isn't hot enough.  Mapp is going to be slow.  Oxyacetylene is the way to go.

Pin and weld is much less hassle.

I am pretty sure I had to go to a specialty store that dealt with high pressure gas fittings to find my silver solder and flux.  I wish I could remember what I initially bought it for 20 years ago.  The last time I used it to reattach a ball to the tip of an antenna after shortening it a few inches.

This - MAPP is a minimum, in my experience.

To braze with Silver solder you need to get the piece to a red heat. For smallish pieces propane works fine, large pieces need a big propane torch or a hotter gas. Oxyacetylene works but it is VERY easy to over heat the work piece and screw up the soldering.

OP, not really hard at all.  If you look through the linked thread it goes into a really good description.  I did mine and it wasn't that bad.  I used the Brownells heat stop paste and it still discolored, so i recommend putting it on as thick as you can.  Use the chalk on the part of the barrel not covered by the paste, as well as the muzzle device.  Not to concerned about the discoloration, because I don't really want it to be a safe queen.  I left the upper in the vice block and tried to spin it off with an armorers wrench after fully cooling and it did not budge.  

It's not pretty by any means, but I learned a new skill and now know a little more  Going to do my brothers this weekend, and his should turn out better.

ETA:  use MAPP gas torch as stated above too.

Pics

Like I said, not pretty, but it is on there and not going anywhere.  Some more advice if you do this: take a qtip and distribute the solder evenly where the crush washer and barrel meet, I suspect this will result in more even distribution of the solder and will likely look much better.  When we do my brothers barrel we are also going to pack the bore with heat stop paste as was recommended by another member in the silver solder thread.

Looks like not enough flux and slow heating.

If you do not use a large enough torch the flux cooks out of the joint before it gets to brazing temp.

Having started with welding first, I always found brazing to be difficult to pickup in retrospect. The few times I have tried it did not work out well.

Clean surfaces, the correct flux, a high silver content solder and don't overheat is all that it takes to get a good solder joint.


In the case of permanent muzzle attachment a pin and a small over weld is very easy and doesn't heat/discolor the barrel.

 

I wondered the same thing honestly, but when I took the wrench to it, I couldn't get it to budge  When I applied the solder, it squeezed out between the crush washer and comp., and also between the crush washer and barrel.  I took a paper towel to get the excess off...  It did take a few minutes to get it to heat where I saw some bubbling and solder start to melt.  Used a MAPP gas torch and thought it wouldn't take as long as it did.  Not going to worry about it too much, like I said it isn't going anywhere  I think I will leave the torch more stationary on my brother's barrel and only move to the other side of the barrel when it starts to get red.

A large enough torch (or tip if they are replaceable) and uniform heating are the key.

Move the torch around when heating.
Make sure the flame is as close to neutral as possible and you are using the tip of the inner cone.

If you are only using MAPP gas consider two torches (and a helper).


ETA

I have wrapped items in stainless foil and used a propane 'weed burner' to preheat them.

Tuck a high temp thermocouple under the foil.
When the temp rise starts to slow down pull off the foil and use any oxy-acetylene to finish up the heating.