Neutering a rifle tech

[Marcus in the Darkus]

I have an AR-15 that I've built up with a pre-ban A1 Colt 20" HBAR upper on a DPMS lower. Because the AWB never sunset here in MA, I needed to remove two of the "evil" features of the upper - namely the bayonet lug and the A2 flash suppressor that came with the upper. I took care of the bayonet lug with a cut-off wheel, a file, and a quick dab of cold blue. I now have a Yankee Hill Machine phantom muzzle brake / compensator, and I need to decide upon a method for permanently affixing it to the muzzle. As I understand it, the BATF-acceptable methods for permanent attachment are:

1. to use silver solder at the circumference of the threaded joint,
2. welding either a bead along half the circumference or four equidistant circumferential tack welds, and
3. blind pin method (pin with a tack weld or silver solder to seal either end of the pin).

I have a MAP torch that I use to light my charcoal grill, and some silver solder left over from my model-airplane-landing-gear-fabrication days, and I also have a drill press and TIG and MIG welders. I don't have a vertical mill or a gun vice or an AR-15 upper receiver vice block. So I'm trying to figure out the best way to proceed.

Is one method preferable to the others in terms of ease of removal of the offending permanent attachment, in the event that I (hopefully) move to a free state some day?

If I go the silver solder method, do I need to sand the finish off the threads or use some sort of flux to get a good solder joint? Is a MAP torch going to do the trick?

If I weld, I'd probably MIG it, because I need practice to get used to the thickness of the part to be welded before I can make an acceptable TIG weld, and, obviously, I only get one shot at this. Any particular advice regarding metal prep?

If I drill and pin the brake to the barrel, do I need some sort of special bit to drill at tangent angle to the barrel, or can I just use a good quality bit and go slow? Do I need to go out and buy an upper receiver vice block, or can I just use some wood or rubber or aluminum in the vice jaws without damaging the barrel?

What about damage to the finish? Either silver solder or a weld will get it pretty hot - does the finish get screwed up and if so, can I just sand it down and hit it with some cold blue?

My apologies for the newbish questions but I really want to get this thing legal and registered here so I can shoot it at an Appleseed shoot in April. Besides, I'm going to have to do a similar neutering to a Yugo M90 underfolder and to a Hungarian AMMS that I'm building.

And for God's sake, please don't tell me to take it to a gunsmith or to ZHA or anything - that's why we have a buil-it-yourself forum.

 

[Romokid]

I have been contemplating using the silver solder method myself. They make a silver solder paste with flux that is in a 1/2 Oz syringe. I have been following a thread on ARFCOM about it. This should be the link http://www.ar15.com/forums/topic.html?b=3&f=4&t=407395
If you read through it there are a few tips like Brownells heat stop that should help. I've found the silver solder flux paste on ebay for about $15 shipped. I think that if you take your time and are careful it can be done.

 

[KMM696]

I used silver solder to put an EGW brake on my A2 upper:

The ATF specified using a solder with a melting point greater than 1100 F - I used Fusion Silver Braze from Brownells. The theory is to degrease the threads on both pieces, spread on the paste, which is a mix of ground solder and flux, put it together and heat with a MAPP torch until the solder melts. I didn't try to remove any finish from the threads, just degreased them.

I did a test fitting of the parts and found because of the tight threads, most of the paste I put on was pushed down into a ring on the barrel, and there didn't seem to be a lot of solder paste left on the threads. I reapplied, being careful to evenly spread the solder on all the barrel threads, put the brake back on, and cleaned off the paste that was pushed down onto the barrel. It went into my vise, and I heated it up to what I hoped was the right temperature/color. I let it cool, and then tried to remove the brake with as much force as I thought the receiver could stand.

It didn't come off.

You can see in the pic the discoloration around the brake and muzzle. I'm not sure if that is actual color changes to the parkerized coating, or if it's a color change because I didn't degrease the outside of the brake and barrel before doing this - I just degreased the threads. It may be an effect of the lubricants cooking off at torch temperatures. When I do this again, I'm going to degrease everything and see if there's better results. The discoloration is easiest to see in this picture - it's less visible in daylight.

I did use an action block to hold the upper while doing this, and a DPMS AR wrench to get the brake on and off. I did use a brake crush washer, both to index the brake and to look the way it should. I haven't tried it, but in theory if you heat the assembly up to 1200 degrees with a torch, you should be able to unscrew the brake once you get to a free state. Sounds like a 2 person job to me. I would assume you would need a tap and die to clean up the threads of the silver solder after they are disassembled.

I also have read that if you want more solder in the joint, cutting a couple grooves the length of the barrel thread with a Dremel cutoff wheel will allow more solder to remain in the joint after the brake is screwed on. The Dremel should cut clean enough that screwing the brake on will clean up the threads. I haven't tried this, but it sounds reasonable.

I used an action block and a 6" vise because I already had them - something like this would work too, with the gas tube removed. Making something similar out of wood might be better - I'd be concerned I'd melt the plastic in the commercial version.

Edit: Found this AR-15 Vise block, too.

I've never welded, or tried blind pinning, so I can't help you there. If I were doing this over again, I'd degrease more and try cutting the grooves in the barrel threads.

Good luck with your project!

 

[economist]

Interesting thread. I have been wondering the same thing. How does this sound:

Drill a pin hole in the comp off of the gun and perpendicular to the center of the barrel when attached. Screw on the comp timed such that the drilled hole is on the bottom of the gun (for aesthetics). Then drill through the hole into the barrel enough so that the pin will hold. Drive in a pin with length that leaves a little space to fill with a MIG weld. File and polish the weld, then touch up. This would minimize the weld job, simplify drilling, and result in a nice-looking result. Opinions?

 

[Marcus in the Darkus]

I've been doing some reading, and I think I'm going to pin/weld the brake to the muzzle. I don't like the idea of drilling the barrel on axis because it would require re-drilling of the pin to get it back out, with a greater potential to screw up and drill into the bore. So I'm going to start by drilling the brake off-axis so that the pin can go all the way through, and just catch the edge of the barrel. Then I'll install the brake, index it, and use the existing hole as a jig to drill the barrel. I'll cut the pin (music wire) a little short so there will be a little depression to fill with a weld puddle. Carefully recountour the tack weld to the countour of the brake with a file, cold blue, and I'm done.

I'm not going to use the silver solder because I don't feel like spending more money on gunsmith supplies or waiting for the parts to get here. Also, I'll be putting a lot more heat into this thing if I have to get the whole barrel end hot enough to flow 1,100-degree solder than I will with a couple simple weld tacks. I want to get this done and sight in the rifle this weekend.

Any thoughts about gripping the barrel with padded jaws in my vice rather than using a vice block?

 

[vicpinto]

Any thoughts about gripping the barrel with padded jaws in my vice rather than using a vice block?

I was reading up somewhere about barreling a FN FAL. The guy used a pair of old sneakers with the rubber soles facing the barrel and stuck the whole thing in a vise. He says it work like a champ and the barrel doesn't spin. I'll have to give it a try.

 

[jon]

I have an AR-15 that I've built up with a pre-ban A1 Colt 20" HBAR upper on a DPMS lower. Because the AWB never sunset here in MA, I needed to remove two of the "evil" features of the upper - namely the bayonet lug and the A2 flash suppressor that came with the upper. I took care of the bayonet lug with a cut-off wheel, a file, and a quick dab of cold blue. I now have a Yankee Hill Machine phantom muzzle brake / compensator, and I need to decide upon a method for permanently affixing it to the muzzle. As I understand it, the BATF-acceptable methods for permanent attachment are:

1. to use silver solder at the circumference of the threaded joint,
2. welding either a bead along half the circumference or four equidistant circumferential tack welds, and
3. blind pin method (pin with a tack weld or silver solder to seal either end of the pin).

I have a MAP torch that I use to light my charcoal grill, and some silver solder left over from my model-airplane-landing-gear-fabrication days, and I also have a drill press and TIG and MIG welders. I don't have a vertical mill or a gun vice or an AR-15 upper receiver vice block. So I'm trying to figure out the best way to proceed.

Is one method preferable to the others in terms of ease of removal of the offending permanent attachment, in the event that I (hopefully) move to a free state some day?

If I go the silver solder method, do I need to sand the finish off the threads or use some sort of flux to get a good solder joint? Is a MAP torch going to do the trick?

If I weld, I'd probably MIG it, because I need practice to get used to the thickness of the part to be welded before I can make an acceptable TIG weld, and, obviously, I only get one shot at this. Any particular advice regarding metal prep?

If I drill and pin the brake to the barrel, do I need some sort of special bit to drill at tangent angle to the barrel, or can I just use a good quality bit and go slow? Do I need to go out and buy an upper receiver vice block, or can I just use some wood or rubber or aluminum in the vice jaws without damaging the barrel?

What about damage to the finish? Either silver solder or a weld will get it pretty hot - does the finish get screwed up and if so, can I just sand it down and hit it with some cold blue?

My apologies for the newbish questions but I really want to get this thing legal and registered here so I can shoot it at an Appleseed shoot in April. Besides, I'm going to have to do a similar neutering to a Yugo M90 underfolder and to a Hungarian AMMS that I'm building.

And for God's sake, please don't tell me to take it to a gunsmith or to ZHA or anything - that's why we have a buil-it-yourself forum.

FYI, Your post sounds very much like you currently have a complete banned rifle in your possession. I think you should clarify that at this time you only have the upper.

 

[Marcus in the Darkus]

No, it's not a complete rifle. Yet. Should be tomorrow, though.

 

[Marcus in the Darkus]

For future reference, I thought I'd post here to follow up.

I ended up blind pinning the barrel. I was too lazy to take pics as I went along (that plus my camera sucks at macro photos). Here's what I did and some hints and tips for those who want to try this on their own.

I wanted to drill a 3/32" off-axis hole about 1/4" into the brake to serve as a pilot hole to allow me to complete the hole after the brake was screwed onto the barrel. The hole was drilled parallel to one of the flat sides on the base of the brake, and located such that it would go slightly into the barrel, maybe 1/32" inside of the minor diameter of the threads on the barrel. I found that the 3/32" drill bit flexed too much and was pushed out of the intended spot because it was being drilled into a curved surface, and not perpendicular to the material. I bet gunsmiths who do this regularly use a steel or aluminum jig that fits tightly against the bottom of the brake with a pilot hole to keep the bit straight. I solved the problem by rotating the brake and drilling a small on-axis starter hole, maybe 1/32" deep, so that when I rotated the brake back the drill had a recess that it could bite into. I also chucked the bit deep, with less than 1/2" of bit beyond the chuck. Once I had the hole drilled about 1/3 the way through the brake I stopped, threaded the brake on the barrel up to the crush washer, then tightened it further to properly index the brake to the bottom of the barrel. Now I had a nice 3/32" pilot hole, so I mounted the barrel horizontally in a drill press vice, used a cross slide table to get the bit perfectly aligned with the pilot hole, and completed the hole through a portion of the barrel and back out the other side of the brake. Then I cut a piece of 3/32" music wire about 2" long, chamfered one end, and used a small hammer to tap it into the hole. I then used a die grinder with cut-off wheel to cut either end of the pin off close to the brake, then I carefully ground the pin down flush with the brake on a bench grinder. This took a little of the finish off the brake near the pin, but I needed bare metal for the weld. Then I fired up my TIG welder, at about 80 amps, and put a little bead right over each end of the pin, with the bead slightly bigger than the pin diameter. Back to the bench grinder where I ground the weld back to to near, but not quite flush with the brake surface. Finally, I cleaned everything up and applied a couple coats of Cold Blue. You can't even see where the pin was welded unless you get right up close to it.

Even though I finished it too late to get to the range this weekend, I'm pretty happy with how it came out! I'm going to give this rifle a good cleaning and lube, and I'll try to post up a couple pics of the finished product.

 

[KMM696]

Nice writeup - sounds like it came out great! That certainly will be less heat applied to the barrel than silver soldering. I haven't gotten into welding yet - but it's on my 'tools to look for' list. Not at the top of the list yet, though.

3/32" would be a tough size to get to bite into a round muzzle brake. I wonder if using a 1/8" end mill to cut a shelf in the brake to start drilling into would have worked, as well.

 

[Marcus in the Darkus]

A couple pics...

The welded pin (this picture makes it look a lot worse than it really is):

The completed rifle:

 

[KMM696]

That does look good - and from the looks of your bench you've got a couple projects lined up, too.

Where did you get the stainless tank from?

 

[Marcus in the Darkus]

I got the tank from Midway USA. Yeah, upcoming builds include a Yugo M90a chambered in 5.56 NATO, a Hungarian AMMS build that I'm converting to a fixed stock (Ironwood designs), and a Ruger 10/22 that was a rusted basket case when I got it (for $50) that I'm not sure what to do with - probably a LTR.