Righting the Wrongs of oxy-acetylene

      If you've been around the milsurp or building community in the United States, chances are you've seen some very exotic or otherwise rare semi auto examples of LMG's or SMG's at some point or another. When you ask the owner where they got it from the answer is almost always "It's a reweld" and that is when the gears start turning. What is a reweld? Can I do a reweld? How is a reweld possible? The answers lie in a series of non-sensical import restrictions compounded over the years along with some good old fashioned American ingenuity.

The Day of the Torch

      As previously covered in our blog post What is a Parts Kit, destruction standards for the importation of machine guns in the United States has changed several times over the past 2 decades. In the early 2000's saw cutting was an accepted process for destroying machine gun receivers and rendering them non-functional scrap metal in the eyes of the law. With some classic back tracking from the BATFE, the destruction standards were revised to now require torch cutting. The actual specifications are pretty detailed compared to previous statutes :

      This information is the current August 2019 guidance retrieved from atf.gov and is accepted as the demil standard now. This very guidance is the current thorn in the side of builders, especially those just entering into the community. Most of the receivers destroyed using this method are intricately machined with tight fitting parts and very complex internal geometry. A lot of the qualities of superb craftsmanship when it comes to military surplus machine guns also leads to very few, if any, US based companies willing to take on the task of creating new semi auto only receivers. In a business sense, it is a very narrow market that requires an immense amount of R&D, tooling, machine time, and so on. This is where rewelds come into play.

What is a reweld?

      A reweld build is just that - welding the torch cut receiver pieces in a parts kit back together while converting it to be a semi auto only firearm. This process is legal in the eyes of the Federal government, since it is considered the construction of a new semi auto only receiver. Do not forget to check with state and local laws as they can vary widely. Most of the time, rewelds are completed by builders aiming for the most authentic example of a particular model for their collection complete with all of the original markings. At the same time, they are performed for builds where there is no other ready made alternative for a receiver. While it sounds rather simple on paper but can be a little more complex in practice. There's a multitude of different variables when selecting kits, metal prep, weld processes, filler material, fixturing, finishing, and so on. With all of these different variables comes the most important one : the builder's welding skill. A quick search on GunBroker reveals a plethora of hastily and poorly rewelded builds that appear to be hanging together with bubble gum and sheer spite. This is the time to mention that reweld builds are not usually a great choice for a first time welder or inexperienced builder. People sometimes need to be reminded that you're going to be putting your face and upper body next to a series of 50K+ PSI explosions. Safety is the key here; any system that bears that much pressure can fail in a catastrophic and life altering way if done incorrectly. Don't attempt to do a build like this if you're unconfident that it will be a safe machine throughout it's service life.

      When it comes to selecting a reweldable kit, there are a few things to look out for. The main one is that whichever kit you're considering comes with all of the scrap pieces! Many retailers that cater to the reweld community, such as myself, are keen to only offer kits with all of the pieces. This saves an immense amount of time for the builder tracking down missing pieces and keeps costs low. Secondly, take a good look at the pieces that come with the kit - are any destroyed to the point of being useless? Even for rewelds, there is a point of no return. Sometimes sections will be so jaggedly and poorly cut that by the time the slag is removed there is little to no clean metal to weld on. Lastly, is there a proven way to convert the receiver to semi only during the build process? Many times this is as simple as adding a denial bar that prevents the insertion of unmodified parts. On the AK/Galil platform it is even easier, and accomplished by welding the auto sear hole shut before getting the receiver to a completed state.

Long Arc, Short Arc, Heli-Arc and In The Dark

      Once you have selected the kit you're going to build, its time to start thinking about which process you want to utilize to weld it back together. There's three main branches that are available to use - SMAW (stick welding), GTAW (TIG welding) and GMAW (MIG welding). All of these processes have their own pros and cons and their own specialized niche in the welding world at large. Luckily, most of these points translate directly over to the realm of rewelding parts kits.

SMAW - Main application is field welding on "dirty" joints or fast fill passes. At home on the pipeline or farm.

Pros :

• Cheap equipment and electrodes 
• Minimal equipment required 
• Does well with less cleanly prepped metal 
• Deep penetration and strong joints

• Welds can get inclusions rather easily 
• Not well suited for thin or delicate work 
• Heat control is hard to master, i.e. blowouts 
• Some electrodes are hydroscopic and need specialized storage

Pros :

• Extreme sensitivity and control 
• Can join dissimilar and non-ferrous metals with ease 
• Open root welds are easier to perform 
• Extremely clean finished welds

• Very steep learning curve 
• Somewhat expensive consumables and equipment 
• Base metal must be very well prepped at every joint 
• Welds can become contaminated easily

GMAW - Main application is fast paced fabrication and structural. Shines in production welding.

Pros :

• Easy to learn 
• Fast 
• Minimal equipment required 
• Cheap consumables

• Shallow penetration
• Very easy to get inclusions and porosity 
• Spatter can be a nuisance to the surrounding work 
• Poor bonding with cold and heavy work leading to cracking

      The key to a great weld is the base metal prep. The rule of thumb I was taught it clean back anything that's not bright base metal within the joint itself and a minimum of 0.5" from the edge of the joint. This includes grinding and chipping off all of the cutting slag, taking off the original finish, and being sure there is no dirt or grease within that area. At this point, its also wise to put a bevel on the edges to help the penetration of the weld into the joint. You may see some people prep their welds with a sandblaster but this isn't a great idea since the oxides used as media can become imbedded in the base metal and act as a contaminate. During the welding process it is paramount to get a solid joint free of any voids, porosity, or inclusions. These create stress risers and therefore weak spots that can propagate into cracks. As seen on one of my early bend tests above, there is an inclusion in the weld that began to form a crack - "When In Doubt, Grind It Out!" is the motto for a reason.

Hot Push and Cold Pull - Fixturing and Welding

      The basic properties of all the materials and elements around us abide by a set of rules called Thermodynamics and these rules cover something called thermal expansion. In short, when almost all materials get hot they expand and when those same materials cool down they shrink. In welding, this can be a make it or break it situation when it comes to fitting piping systems or precision fabrication. Sometimes metals base metals will expand or contract at different rates than the filler metal used, sometimes the joints themselves will cause a flex across the entire work leading it to be out of true, and sometimes when the joints cool down the work is shorter than called for. This is where fixturing comes in. Any form of clamp, vise, jig, etc. is considered fixturing. This is essential to getting a precise fit up not only for the initial welding but also to make sure the spacing of the joint is adequate to account for shrink after the weld cools off. There are many different forms of fixturing out there for all sorts of parts kits, many builders will even machine their own to save on costs. Sometimes with simple kits, such as the PM-63, the only fixturing required is a straight edge and some clamps. The most important part of fixturing is alignment combined with accounting for shrink. There have been many times where a builder will get done with a full reweld only to discover that certain pin holes are off by as much as 1/8" of an inch. Its not just one joint that will shrink, its all of them across the entirety of the work!

      The actual welding itself is rather straight forward, using the knowledge from prior welding experience. Sometimes the gaps in the torch cut receiver pieces can be big enough to require cut pieces of filler metal. In the world of pipe welding, getting the "weld on the inside" is called rooting. It's an odd concept to explain but at its core uses the heat and penetration of a weld process along with proper gap spacing to weld the inside from the outside. I highly recommend reading up on the process and trying it out if you're interested - its a fantastic skill to have and can make rewelds a breeze. While performing these welds, most people like to use backers during the process to minimize internal weld finishing. An important point to note: ferrous metal welds don't adhere to copper or aluminum, making them the preferred choices for backers. Most fixtures and jigs are already constructed out of these materials. Be sure to complete all necessary semi auto modifications before the receiver has reached a completed state. Many people will say to heat treat your receiver after welding it. I have yet to see a receiver suffer a catastrophic failure from NOT heat treating. Keep in mind, all treatment was lost once it was cut with a torch.

The ol' In and Out - Finishing

      Most finishing in the welding world is going to be done with a combination of an angle grinder, Dynafile, and Dremel. The key to using these tools is knowing when to use the right grits. A grind wheel is fast material removal for bringing everything flush, low numbered grit sanding belts and for blending, and progressively higher number grits for evening and eventual polishing if desired. The key is to let the grits do the job and not to dig. Digging with your abrasives will create a "dished" look that is almost impossible to get rid of short of using auto body filler. I still look at my "Four Hour Galil" and can't stop focusing on the dished marks from me hurrying to get done! Take your time, attention to detail is the key to a professional looking build. For more advanced builders, a milling machine can be used for this process and is an excellent way to recut internal features. Do not fret if you don't have a milling machine, a steady hand and a Dremel can do most of the internal work and get it to a reasonable state of function. Lapping compounds are also great ways of getting parts to reintegrate their sliding fits, such as bolts in rails and carriers against their denial pins. Do not forget to clean it out of all the crevices in your build before further work - the grit can cause all sorts of malfunctions later down the road.

      At this stage most builders will be considering some form of cosmetic finish. There's a multitude of options out there including hot caustic blue, rust blue, Duracote, Cerakote, cold blue, and my personal favorite high temp header paint. Consider which finish is easiest for you to apply and will match your build. Bluing rewelds tends to yield varied results because the welds often take on a different color than the base metal. Cold blue is also notorious for the smell that it leaves on your hands, but it color matches traditional bluing rather well without all of the fuss. I prefer header paint for most, not all, of my builds due to its ease of application and solvent resistance. Despite all this information, I refrain from applying cosmetic finishes until I've completed the tuning process. All of the constant disassembly, adjustment, and general work on the build can wreck a pristine finish.