Silver soldering

[bkjeffrey]

Can anyone explain the process of silver soldering a flash hider on an AR15 barrel? I got a great deal on a Daniel Defense 14.5" barrel but I need to attach a flash hider permanatley. I want to use silver solder verses pinning it because I dont want to drill into the barrel and I may want to remove the FH one day to change it out.

 

[Ronbo256]

To make it "ATF Legal" you need to use 1100 degree silver solder to PERMANENTLY attach the flash hider/muzzlebrake to make it over 16" in length. Alternately you could pay the tax and jump thru the hoops to register it as a SBR. I'm not sure I would be able to remove a threaded attachment that had been silver soldered properly. I'm sure if I'm wrong, someone will be by in a few minutes to correct me BTW AFAIK simply owning the short barrel and an AR without the permanently attached extension is illegal, similar to owning a m16 auto sear and an AR, you may possess one or the other legally, but not both. The only exception is if you have an AR lower registered or marked as a pistol.

To try to answer your question, silver soldering is a form of "brazing" with a filler material made of higher melting temperature than common lead solder. You need to attach your flash hider , and using a torch heat the barrel/ flash hider joint until the silver solder melts and flows into the junction. Do not use the torch to "melt" the silver solder and drip it onto the barrel, it needs to flow so you apply the solder without the flame on the part you are soldering. I would think a common plumber's propane torch would provide enough heat. here is a little guide, if you have never done this kind of stuff you might want to practice on some copper tubing from the hardware store first.

http://factoidz.com/a-diy-guide-to-silver-soldering-techniques/

This site has some silver solder/flux paste in a syringe that seems like it would do the job nicely and legally.

http://www.shorinternational.com/Solders.htm

 

[bkjeffrey]

Thank you for your response. Just to put this out there, I do own a registered SBR that I personally built on a Form 1. With that I have a very good understanding of NFA law and ATF rules guiding the installation of permanent barrel extensions.

However, I do not understand the silver soldering process. I am quite experienced at soldering copper tube with lead and paste flux.

Wouldn't soldering a muzzle break require the use of flux to pull the solder into the threads?

 

[Jolly Rogers]

I believe Silver solder is like brazing in that it needs flux too. Surface prep is extremely important also. The metal that is added for the joint is in between tin lead solder and brass used for brazing with regard to heat required. MAPP gas would be a minimum to silver solder.
Joe

 

[bkjeffrey]

I just checked the link provied by Ronbo and the silver solder paste with flux looks like a good idea. The easy silver melts at 1240* also. Thanks for the link!

Anybody have an opinion on using this?

 

[Jim K]

Silver soldering requires enough heat that it can damage the barrel, both outside and inside, unless heat resistant paste is applied liberally to those areas you don't want to damage.

Jim

 

[dfariswheel]

I'd recommend the lowest melting point silver braze (solder) you can.
Brownell's sell a 1100 degree version.

The easiest to use is the solder/flux paste type.

To do the job, first use a solvent and a wire brush to thoroughly clean and degrease the threads on the barrel and the muzzle attachment. If neither is threaded, clean what you have.
Wipe all oil out of the bore so it won't burn into a sticky mess inside.

Mix the solder paste if necessary and apply a thin coat on the barrel and more on the attachment.
Screw the attachment on the barrel and spend a little time making sure it's aligned properly.

Once you're sure, use a BIG torch to quickly heat the attachment and barrel until the solder flows. Pull the torch away, then walk away and let everything cool on it's own.
DO NOT quench the barrel in water.

You want to use a big torch so you can heat the barrel as fast as possible to limit heat spread.
After everything is completely cool, use hot soapy water and a brass brush to scrub the area to clean it up.

 

[HD_Ride]

what about Tig Weld? one small tack underneath and you're done.

 

[DBR]

If you pin the barrel extension and then tig weld the head of the pin you avoid heating the barrel (a bad thing) and you can easily drill out the weld and pin if you ever want to remove it. Melting out a silver brazed connection will involve a lot more heat at the the end of the barrel than I would want.

 

[Ronbo256]

Sorry didn't mean to lecture on NFA rules, but I couldn't tell your level of knowledge from the post, especially the part about wanting to remove it later. Yes you will need flux specifically designed for silver solder. To answer HD's question, the small TIG weld would not pass the ATF's anal exam for "permanently attached" Once it's silver soldered in place it's there. dfariswheel has a much better writeup than me. Thank you dfariswheel. I agree DBR that would be the best way to satisfy NFA rules and still be able to remove it later, but the OP said he did not want to "pin" the flash hider on.

 

[DBR]

Yes, I know the OP didn't want to pin the muzzle device. However sometimes people make their decisions without adequate knowledge of the choices.

I don't think the OP fully understands the trivial consequences of drilling a blind hole in the threaded part of the barrel vs heating the whole thing to temperatures that will permanently alter the metallurgy of the barrel.

 

[Ronbo256]

DBR, point well made.

 

[jester_s1]

How is it going to alter the metallurgy of the barrel? Unless the barrel is made of a hardenable steel and has been hardened a tempered, there won't be any change with the 1200-1300 degree heat unless I'm missing something.

 

[DBR]

Assuming (yes that word) the barrel is made of cold drawn bar stock (common) 1200* is in the annealing range for steel and may soften the barrel. If the barrel is made by more sophisticated means and actually heat treated it will alter the heat treat. If the barrel has a hard chrome lining it may also affect that as well.

My approach to these kinds of modifications is to do the least harm based on realistic assumptions about the materials involved.

Added: any decent AR barrel is at least 4140 CRMO steel and more likely 4150 CRMO. Heating and then improperly cooling these steels can make them very brittle. If they are cooled slowly they won't be brittle but they will be soft. In either case you have altered the design properties of the steel.

 

[BBBBill]

... the small TIG weld would not pass the ATF's anal exam for "permanently attached"...

When did the rules change? It has been stated (in the past) in ATF's regs/rulings that blind pinning with welding over the pin head did in fact constitute permanatly attached.

 

[Ronbo256]

BBBBill, HD didn't put the pin on it, he just stated to tack TIG weld it. Pin AND weld over the pin is still fine.

 

[o Unforgiven o]

When did the rules change? It has been stated (in the past) in ATF's regs/rulings that blind pinning with welding over the pin head did in fact constitute permanatly attached.

He was talking about mounting the flash suppressor and just tacking it at the back.

 

[MrCleanOK]

bkjeffrey,

Pin/weld is the less-permanent way of doing a permanent muzzle device.

 

[jester_s1]

Assuming (yes that word) the barrel is made of cold drawn bar stock (common) 1200* is in the annealing range for steel and may soften the barrel. If the barrel is made by more sophisticated means and actually heat treated it will alter the heat treat. If the barrel has a hard chrome lining it may also affect that as well.

My approach to these kinds of modifications is to do the least harm based on realistic assumptions about the materials involved.

Added: any decent AR barrel is at least 4140 CRMO steel and more likely 4150 CRMO. Heating and then improperly cooling these steels can make them very brittle. If they are cooled slowly they won't be brittle but they will be soft. In either case you have altered the design properties of the steel.

If it's cold drawn steel then the steel was annealed already before the barrel was made. The two steels you mentioned are not made for a harden and quench process, so heat treating isn't a part of the process anyway. If the barrels had been hardened the way springs or trigger parts are, then 1200 degrees would draw some hardness from them, but not anneal them. But since barrels aren't done that way, there's nothing to worry about. The only way there is a chance of altering the metallurgy of the barrel is if he goes above critical temperature, which IIRC for those steels is around 1650. A cold water quench would then harden the barrel somewhat, which might be an issue if it doesn't crack from a stress riser. Gunsmiths and manufacturers have been silver brazing on barrels for a long time, so if it did something to hurt them I suspect the technique would have faded out of use by now.

 

[bkjeffrey]

Ooops......

Yes, I know the OP didn't want to pin the muzzle device. However sometimes people make their decisions without adequate knowledge of the choices.

The OP may want to remove the perm. attached FH at a later point to install his suppressor and pin the upper on his SBR lower. Thats why the least intrusive method of "permanatley attached" FH was seeked. Figuring that its a $250 Daniel Defense barrel. Im my mind solder was it, because I have used heat to unsolder copper tube to re-engineer plumbing. But now that were questioning the structural integrity of the muzzle by applying numerous heat/ cool cycles over the life of the barrel I dunno.

Pin/weld is the less-permanent way of doing a permanent muzzle device.

I'll play your game, please explain. If I drill a hole through my FH into the threads of my muzzle, your suggesting that I could at a later time remove the pin and still have enough thread integrity to positivley mount my suppressor to the remaining threads?

 

[Jolly Rogers]

I should think the pin recess in the threads would not preclude re-using the barrel. Lots of threads left after the pin is removed.
Joe

 

[Ronbo256]

plus you can always run a die over the thread to straighten out the buggered up area of the thread which will be small compared to all the remaining thread.

 

[Big Az Al]

When removing A pinned FH, grind as deep a needed to find the the pin(s) once you can clearly see that you are past the weld, turn the FH forward and back just a little each way until the pins raise up and sometimes fall out then unscrew the FH.

Easy on the barrel, hard on the FH.

But heck sacrifice a what 25-35 dollar part, to stay legal, and also take it easy on a more exspensive barrel? TO myself that is a win win situation!

 

[bkjeffrey]

But heck sacrifice a what 25-35 dollar part, to stay legal, and also take it easy on a more exspensive barrel? TO myself that is a win win situation!

Agreed. To wrap up the discussion I went ahead and passed on the 14.5" and just a 16". Less hassle, less worries, less problems and more versatility.

 

[HisSoldier]

any decent AR barrel is at least 4140 CRMO steel and more likely 4150 CRMO.

The two steels you mentioned are not made for a harden and quench process, so heat treating isn't a part of the process anyway.

I must be missing something, 4140 and 4150 are heat treated all the time, one common form is "prehardened". We have made many parts of 4140 and sent them out for heat treating. I just didn't want to let that misinformation stand, but like I said, maybe I'm missing something?