Full auto spare parts

[jmorris]

Never have welded an AR receiver made from any material, why I said it would help if we were outside the hypothetical. All I said was 7075 aluminum can be welded because I have done it.

I have seen a number of polymer lowers that were broken and even a few aluminum ones that were damaged but the cost of a non transferable lower isn’t enough to offset the cost of a repair on either.

Like I said before, give me (I’ll cover shipping and transfer costs) a transferable lower that “cannot be welded” that once I repair it, would be worth somewhere around $20,000 and not only will I let you know how I did it, I’ll create a new threat complete with step by step photos.

 

[AlexanderA]

All this discussion about repairing transferable M16's (by welding) overlooks the key take-away: you don't want to damage such a valuable gun in the first place, so that a repair is necessary.

Economics dictate that soon, at least the higher-end MG's will represent such a large investment that it would be foolhardy to shoot them at all. Even taking them out of the safe involves a risk of damage. (That is, unless you're the kind of person who lights his cigars with 100 dollar bills.)

I have a Colt M16 that is unfired and has its original box and accessories. I wouldn't dream of taking it to the range.

 

[MachIVshooter]

I suppose it might be easier if we were outside the hypothetical and were addressing an actual failure. A repair on an out of round pin hole in a 7075 receiver is pretty easy to do. A receiver plasma cut into a number of parts would be much higher on the difficulty scale.

The kind of failure likely to happen that would tempt one to weld would be a broken off RE housing, and it would break again and again if welded.
Nobody is going to scrap a $17,000 receiver over sloppy pin holes that can (and should) be repaired by reaming and pressing in bushings.

Nobody is going to plas or torch a transferable lower, and nobody who has any familiarity with plasma cutting uses it on aluminum outside of very controlled environments. Bad juju right there. Messy, toxic without PPE, extreme UV light, and very dangerous with certain alloys around moisture.

 

[pintler]

JMorris: I'm still confused by the process. I get CNC controlled laser welds of two sheets or tubes with no filler, etc. That's a fairly different process than a manual weld with filler. I'm curious for the details because I'd like to research how the metallurgical problems you would have if you TIG welded 7075.

So, is the process you use a manual one? Or if it's CNC, how do you follow an irregular crack? Who sells the equipment? What kind of filler do you use? How deep a cross section can you weld? How much can you build up?

 

[jmorris]

Nobody is going to plas or torch a transferable lower...

I agree it’s about as likely as a guy being “screwed” because his pre ‘86 M16 lower cracked down the middle, I was just thinking about two different extremes in problems to repair.

 

[pjeski]

All this discussion about repairing transferable M16's (by welding) overlooks the key take-away: you don't want to damage such a valuable gun in the first place, so that a repair is necessary.

Economics dictate that soon, at least the higher-end MG's will represent such a large investment that it would be foolhardy to shoot them at all. Even taking them out of the safe involves a risk of damage. (That is, unless you're the kind of person who lights his cigars with 100 dollar bills.)

I have a Colt M16 that is unfired and has its original box and accessories. I wouldn't dream of taking it to the range.

That’s why I won’t buy a new in the box gun to keep as an investment. I shoot all of my transferrables.

 

[jmorris]

I'm curious for the details because I'd like to research how the metallurgical problems you would have if you TIG welded 7075.

The problems you can have is weld failure and that is why it is not a common practice in most circles.

If I have no other option but to repair a part made of 7075 I use 4043 or 5356 and limitations on how thick and how much you can build would be dependent on the same factors as other alloys of aluminum. Most of the welding I have done on “unweldable” aluminum alloys has been AN fittings or creating ones that didn’t exist from ones that do in 2014, 2024 and 7075.

Since 1997 or so I have had an interest and sort of follow metal deposition process too. Not a lot specifically with 7075 but here is one.

http://www.ysxbcn.com/down/2014/06_en/27-p1836.pdf

 

[pintler]

Alas, I'm still in the dark here. IIUC, you think it's practical to repair weld 7075 AR receivers. You have posted two links about laser welding, and one on 3D printing. I'm still unsure what process you envision using? Some kind of manual laser welding? CNC laser welding? If so, how do you generate toolpaths?

There are lots of odd corners in the welding business - you can weld steel to aluminum, for example, using explosive welding - but I doubt one can practically use explosive welding for repairing AR lowers, for example. So I'm trying to get at the basics of the process you envision when you have that cracked lower in your shop - manual? CNC? Laser? Ion beam? 3D printed somehow? Are we talking a $100K welding machine, or what?

 

[CLP]

perhaps a challenge is in order? cheap lower, chop it, repair it, and put it through a torture test

 

[jmorris]

So I’m trying to get at the basics of the process you envision when you have that cracked lower in your shop...

Just like any job I do, it depends.

Not unlike a car is broken, what you do as a repair to it depends on what is wrong with it.

With an automobile that is worth very little might be “totaled” with some problems. All the while a car that is much more valuable folks would put in a little more effort to take something that would otherwise be considered ready for the junk yard or scrap pile and repair it.

Let’s say we have a receiver that is a machine gun on a form 4, it would be worth somewhere around $20,000 vs a semiautomatic version of the same thing closer to $50. That is a 400:1 price difference, if we doubled the cost of a semi lower to $100 it would still be 200:1 difference. I have done lots of stuff to save less money.

To keep the math simple, say we are talking about $100 an hour rate for repair, you would need to be able to repair a $50 lower in 30 minutes to break even. You would need to repair the $20,000 lower in 200 hours or 5, 40 hour weeks, to do the same.

We still don’t have a single example of a “screwed” lower on a form 4 so pretty hard to say what would be a repair. I am still ready to make the thread, if we can come across one though.