Damage to the end of a barrel...

[Quizcat]

I used a pipe thread cutter to remove a 1/2" long barrel shroud from in front of the front sight post of a Saiga 7.62 x 39mm Rifle barrel, in order to thread the end of the barrel for a muzzle device.

Unfortunately, I made an error gaging the depth of the pipe cutter wheel in an attempt to remove the barrel shroud, and the tube cutter wheel did cut into the OD of the barrel deeper than the depth of the shroud itself.

Upon close inspection where the groove in the OD of the barrel was cut I noticed an anomaly on the ID of the bore, right where the groove on the OD had been cut. It appeared to be more of a concentric crack in the barrel all around the ID of the bore exactly where the groove had been accidentally cut through the barrel shroud and into the OD of the barrel. A .300" pin gage still cleared the bore, but there was some scraping along that "crack" in the ID of the barrel.

So, rather than chance it with respect to safety and accuracy, I decided to cut off the 1/2" of the end of the barrel right where the groove had been cut, reface the barrel to 90 degrees, then recrown the barrel to 11 degrees, just like the original. Now, a .300" pin gage drops all the way down to the breach, slick as a whistle, totally unobstructed.

Next, I'll use a hollow mill, rather than a tube cutter, to remove what's remaining of the barrel shroud in front of the front sight block, about .500" long, then I plan to thread it for a muzzle brake. I'll be using a guide arbor inserted into the bore on the thread die so the threads are sure to be concentric with the bore.

I'm about .250" short of the required 16" barrel length after removing .500" off the end of the barrel. So, I plan to permanently attach the muzzle brake using silver solder so that the overall barrel length will be in compliance with the muzzle brake permanently afixed to the barrel.

I'll need to obtain an MAPP torch, and some high temperature silver solder (minimum 1100 degree) in order for the installation of the muzzle brake to be within compliance. I've never had to silver solder a muzzle device before, but think I'll prefer it to a pin and weld method with respect to aesthetics.

With the refacing and recrowning completed, is there any reason to test fire the rifle for accuracy and function before I remove what remains of the barrel shroud in preparation for threading the barrel for the muzzle brake?

Any pointers on silver soldering the muzzle break?

 

[Riomouse911]

Since it sounds like you have machine shop skills and tools, why not avoid all the expense and hassle of buying a silver solder rig and instead thread the barrel? Then you can attach a flash hider, brake or other device to bring it over 16” and make it legal.

Using a drill press drill through the bottom of the flash hider and into the barrel a bit, then use a cut-off drill bit or other hardened steel peg to create a pin for the barrel before welding over the hole? A bit of file work, hi temp paint to match the barrel color and you’re all done.

I pinned a Phantom to my BCM 14.5” upper using the above drill press and drill bit peg years ago. It took me under an hour, the weld is hardly noticeable and worked like a charm..

Stay safe.

 

[shoobe01]

+1 to thread on attachment, then weld over. Silver solder is more effort than it's worth and despite being legally permissible, seen a few fail, at which point expensive repair PLUS you could have legal issues.

 

[Quizcat]

Federal Law requires PERMANENT attachment of a muzzle brake on a rifle barrel under 16" in length. My rifle barrel is under 16," and with the addition of the muzzle break, it will be over 16".

So, "Permanent Attachment" is defined only three very specific ways by ATF. I must install the muzzle brake in accordance with federal law, or I'm subject to prosecution, years in prison, and enormous fines.

Silver soldering (minimum 1100 degree) is one of the three methods dictated by ATF as one of the only acceptable methods for permanent attachment of the muzzle brake. I've checked very thoroughly into the silver solder method, and it's widely used without having any repercussions to barrel metalurgy or barrel integrity. The ATF requirement stipulates a minimum heat level of 1100 degrees.

The other two ATF approved methods of legal "permanent attachment" of a muzzle brake include either pinning/welding the muzzle brake in place, or welding the barrel at the joint where the end of the muzzle brake meets the barrel at four points along the joint, with at least four weld points equal distant apart.

If done correctly, in my own opinion, silver soldering is the most aesthetically pleasing. Pinning/welding, or welding the joint at four locations can turn out pretty ugly for those of us that are unskilled at welding, or for those of us that don't have a tig welder, which is the preferable method to pin/weld, plus tig welds still require a lot of clean up. I don't own even a mig welder, nor do I have that experience. I'm not disintrested in learning to weld, but silver soldering is far cheaper with respect to the cost of new equipment, and accessories, even were I to mig weld or tig weld it myself.

The equipment to silver solder is infinitely cheaper than buying a tig welder, and taking the time to learn how to use a tig welder, which requires a lot more skill and practice than mig welding. I could prepare it for pin/weld, and take it to a pro welder, but I prefer to buy the MPP torch, silver solder, and heat shield compound, rather than paying a pro welder. I would also like to learn how to properly silver solder it myself.

It's understandable that some might believe that to heat the barrel could effect the metalurgy. But, my research shows that heating the barrel to 1100 degrees has no effect on barrel metalurgy or barrel integrity. However, in order to isolate the heat from any other areas of the barrel, other than the muzzle threads and solder joint, it's a good idea to utilize a heat shield compound ahead of the thread area so that only the threads and the solder joint receive 1100 degrees, enough to properly silver solder the muzzle brake in accordance with ATF regulations, while not possibly inadvertently affecting the metalurgy of the barrel with accidental amounts of heat in excess of 1100 degrees.

I might need to use some high temperature engine paint to achieve a uniform finish appearance if the muzzle brake is discolored from the silver soldering process. I've used Duplicolor DE1634 Flat Gloss Engine Paint (500 degree) in other areas on numerous other AK47 Saiga Rifles I've built, and it matches the finish on the rifles perfectly. Fact is, at Izhmash in Russia, where these rifles were manufactured, they used a proprietary paint to finish all of the rifles coming off the line, both on the civilian models, as well as fully automatic military issue AK47s for the Soviet military. There isn't any particularly durable or exemplary finish applied to these rifles other than plain old paint. Iszmash paint is a durable paint, but so is the Duplicolor engine paint in my experience.

I have already decided to silver solder it because it's an ATF approved method, and while I know there have been botched silver solder jobs done by some, it's still a widely used legally acceptable method used by many gunsmiths. When it's done right, it's much more aesthetically pleasing, cheaper, and quicker.

So, not having done silver soldering before on a muzzle brake, as part of my research, I'm seeking any pointers on silver soldering muzzle brakes from those that actually have done it successfully.

 

[BBBBill]

Silly solder or TIG will work well. To protect the barrel from heat when soldering, be sure to plug the bore with heat control paste directly under the area to be soldered and a couple inches either side for insurance. The duration of the heating process when soldering is much longer than that when TIG'ing, so the barrel heat soaks longer. I've seen bad heat scale form in a bore from soldering, leaving a permanently rough bore when there was nothing to keep oxygen from the surface. Not a bad practice when welding either. That's why I prefer a tiny spot of TIG over a pin head, but as long as you protect the bore you should be fine.

 

[Quizcat]

Silly solder or TIG will work well. To protect the barrel from heat when soldering, be sure to plug the bore with heat control paste directly under the area to be soldered and a couple inches either side for insurance. The duration of the heating process when soldering is much longer than that when TIG'ing, so the barrel heat soaks longer. I've seen bad heat scale form in a bore from soldering, leaving a permanently rough bore when there was nothing to keep oxygen from the surface. Not a bad practice when welding either. That's why I prefer a tiny spot of TIG over a pin head, but as long as you protect the bore you should be fine.

Good advice, thank you!

 

[MCFLYFYTER]

Being a welder and having used a mapp gas torch, I personally wouldn't try it without oxy fuel of some sort. It will take forever to get everything hot enough with mapp. You could drill it out and take it to any welding shop that would tack a pin for $20. Silver solder ain't cheap either, combined with the fuel and flux cost. Pinning has essentially zero risk, as long as you can run a file.

I would also heat and flux the threads before assembling, then just flux, flux flux. When you think it has way too much flux, add some more. In case you were thinking of checking temps with an infrared thermometer, don't. The emisivity will not be correct for a curved object of a random color. They can literally be hundreds of degrees off.

Good luck

 

[Quizcat]

Being a welder and having used a mapp gas torch, I personally wouldn't try it without oxy fuel of some sort. It will take forever to get everything hot enough with mapp. You could drill it out and take it to any welding shop that would tack a pin for $20. Silver solder ain't cheap either, combined with the fuel and flux cost. Pinning has essentially zero risk, as long as you can run a file.

I would also heat and flux the threads before assembling, then just flux, flux flux. When you think it has way too much flux, add some more. In case you were thinking of checking temps with an infrared thermometer, don't. The emisivity will not be correct for a curved object of a random color. They can literally be hundreds of degrees off.

Good luck

I do have a good relationship with one of our professional weld shops of very good reputation, and they've even done stuff for me for free when the jobs have been small. So, maybe they would handle it cheaply, or even free...making the pin/weld option the better choice after all. I know they would do a good job of cleanup, they're pros.

I've always been interested in getting a welder, and learning about it. But, I would have so little use of a welder, generally speaking, that the cost of equipment, and then the added cost of all of the neccessary accessories, ie: weld table, decent helmet, good welding gloves, etc...and more importantly, a lack of available space in the out building, which is what I would want to get started in it the right way. I could just never really justify getting into it. I actually had taken delivery of a cheaper welder from Northern Tool a couple years back, but I ended up returning it when I realized the amount of space I would need to learn the skills the right way.

Thanks so much for the advice about the limitations with the MAPP torch, and having to employ oxy fuel to do it right. Your comments, and the advice of others in the forum recommending pin/weld have me reconsidering pin/weld as the better option.

Thanks all!

 

[MCFLYFYTER]

Mapp will work, it just depends on the mass you need to get up to temp as to how long it will take. It is safer in that it would be harder to melt the exterior, but the barrel will be soaking up the heat fast and it can take a lot of heating to overcome the 16"of heatsink.

This is from armalite, but your barrel is likely not the same composition, but 1100 degrees is hot, and is nearly guaranteed to make permanent changes to the grain structure

Effect of heat on the barrel.
In addition to increasing the malfunction rate, excess heat weakens the material of the barrel.

The barrel of the M4 carbine is made of chrome-molybdenum-vanadium steel, and is chrome lined. It is an extremely high quality grade of steel capable of long service. This steel tolerates high temperature well. At a temperature of approximately 1100 degrees, however, the structure of this alloy undergoes a permanent transformation that substantially, and permanently, alters it. The steel becomes prone to rupture under high pressure. It may not fail at the time of overheating, but instead may fail at a later date and far lower temperature. This confuses the user as to the reason for failure

http://www.brokenguns.net/downloads...arrel Design on M16 Functioning - tnote48.htm

 

[BBBBill]

Since you are reconsidering TIG - It only takes a 1/4" max spot of TIG to cover a blind pin head. If you put it on the bottom of the barrel it will be practically unnoticeable. Plugging the bore with heat control paste is still a good idea just to cover all possibilities. I would not try to hide it completely as some overzealous LEO might take it on himself to try to prove that you are in violation. Lots of good cops, but I've known a few bad ones. I used to volunteer as a pilot for the local PD so I got pretty good insight into the culture.

 

[doubleh]

On the pin: First off drill bit shanks aren’t hardened, only the twisty part is. Second thing: Any hardened pin you install will no longer be hard after welding it in place. Even a small tig tack weld on something of that size is going to anneal it. Tig rod would be a good source for pin material. I keep an assortment of diameters on hand just for that use.

 

[Quizcat]

On the pin: First off drill bit shanks aren’t hardened, only the twisty part is. Second thing: Any hardened pin you install will no longer be hard after welding it in place. Even a small tig tack weld on something of that size is going to anneal it. Tig rod would be a good source for pin material. I keep an assortment of diameters on hand just for that use.

Thanks for the tip. I plan to take it my local weld shop, and have them tig weld it. I drilled the muzzle brake with a 1/8" drill bit, and then I put a divit into the barrel to about the depth of the muzzle break's barrel thread with the same 1/8" drill bit. I'll be sure to mention to them about using the tig rod for a pin. I'm a little skittish about drilling too far into the barrel, so I'll consult with their tig welder as to whether the divit needs to be any deeper. They can do it there if the pin hole needs to be slightly deeper.

Since I'm not really up on welding, I was wondering if the heat from the tig rod creates a good weld point all the way to where the tig rod contacts the bottom of the thread depth into the barrel wall, or just around the periphery of the tig rod, and at the surface of the weld, which just causes the pin itself to block the muzzle brake from turning? In other words, I'm not sure if the tig weld becomes homogenous with all of the barrel material, or if the tig weld just attaches the tig rod around the rod's periphery, and at the surface of the weld, causing the pin to just mechanically block the muzzle brake from turning.

 

[doubleh]

I would have the outer end of the pin just slightly below the outer surface of the muzzle brake. A tig welder that knows what he is doing can fuse (that means melt the metal) the outer end of the pin and the brake about flush. All you need is the outer end to fuse and it will stay in place. Barring taking a pipe wrench to it and completely ruining the threads it's not going to be movable.This could also be done with an acetylene torch if you can find a welder today that knows how to use one. The good thing about tig is that it is so fast that it puts much less heat into a weld than an acetylene torch does. Tig welds are just as strong as other methods of welding as long as the welder knows what he, or she, is doing but that goes for any welding process. For bonafidies I spent most of my working life as a welder. Shaky hands has put that skill to rest.

 

[edwardware]

I've always been interested in getting a welder, and learning about it. But, I would have so little use of a welder, generally speaking. . .

After years of mild interest, I bought a Hobart 100 in January. . . and you wouldn't believe how many projects I've welded since then. I even re-timed my Rem700 ejection lug (after 2 weeks of practice on mockups).

Turns out a glue gun for steel is wicked useful and lots of fun. I'm into it less than $500 all told.

 

[BBBBill]

I'm not sure if the tig weld becomes homogenous with all of the barrel material, or if the tig weld just attaches the tig rod around the rod's periphery, and at the surface of the weld, causing the pin to just mechanically block the muzzle brake from turning.

The pin is only welded to the muzzle brake/flash hider. It does not weld to the barrel itself. As doubleh noted it is sufficient to prevent removal with normal forces using normal hand tools. Anything can be broken with enough force, but that is not the intent of the BATF rules. Welding the head of the pin is sufficient to satisfy the rules.

 

[doubleh]

Something I forgot is that if you wish to remove the brake at a later date the tack weld is easily removed by drilling or milling it out. Personally I would use a an end mill but I'm set up to do so.