Bent AR Upper Receiver

[Virg1L]

A few months back my dad and I were aligning a stubborn gas block on my lefty-piston AR. In the process, we managed to bend the upper on the strip just under the ejection port. We did not have a vice at the time, so we used leather and tape-wrapped wrench to bend it back. After a lot of elbow grease we managed to straighten the bend to where the bolt carrier would move freely and the upper sat almost perfectly flush with the lower (less than 1/2 mm, wouldn't notice it if you you didn't know it was there). Also, the barrel was attached during the bending and fixing though steps were taken to ensure no strain was put on the barrel.

Months later, I'm checking the action and notice the bolt carrier slightly catching on the side, as if its going through a tight space. It still moves with full range, but needs a very gentle push to get past that spot. Upon inspection, I noticed some stretch/stress marks in the lower corner of the upper in front of the ejection port.

Now, if this were a direct impingement AR I would be very concerned about heat deforming the bend and causing damage/injury. However since this is a piston, I'm not as worried. I hear the spot under the ejection port is the weakest part and that this a common problem. I want to try avoiding having to buy a new barrel, if possible, and that I can just rework the spot where it's trying to bend back.

What are your thoughts/experience on this? Should I be worried about the stress marks or is this a simple fix?

Thank you

 

[madcratebuilder]

IMHO it's unsafe to fire. Aluminum has no fatigue resistance and this upper has been structurally compromised when you bent it. Uppers are dirt cheap, replace it. It's not worth the risk of it coming apart and injuring someone. Not to mention the legal issues if there was any injuries.

 

[rjrivero]

My opinion is also that you need a new upper receiver. Consider it another payment to your PhD in firearms.

 

[mljdeckard]

DI or piston doesn't matter. When that metal is compromised, it won't go back. Scrap it.

 

[Taurus 617 CCW]

You need a new upper receiver. Make sure to use an AR-15 receiver jig when any torque needs to be applied (barrel nut, compensator, etc.).

Here are a couple of examples:

http://www.brownells.com/.aspx/pid=22385/Product/AR-15-M16-UPPER-RECEIVER-ACTION-BLOCK

http://www.brownells.com/.aspx/pid=17094/Product/AR-15-AR-STYLE-308-UPPER-RECEIVER-BLOCK

Don't use this type for torquing because it doesn't support the receiver:

http://www.brownells.com/.aspx/pid=27411/Product/AR-15-M16-UPPER-RECEIVER-VISE-BLOCK

 

[Redlg155]

Replace the upper. It will nag you to no end if you don't.

I noticed that you said "Lefty", so you are limited to a couple of manufacturers for a replacement upper. I'm guessing you probably have a Stag Arms upper reciever.

A new one will set you back a little more than a standard reciever. I'm not sure if stock upper reciever blocks will work without modification, but mods should be easy.

 

[4v50 Gary]

New upper. Old one is good for a display.

 

[Virg1L]

Ok Then.

One thing I've learned from this forum is that no two people rarely agree on one thing. So naturally once I came back and saw every single post say to replace it, I knew there was no salvaging. It's a shame but an easy fix... In theory.



I admit I didn't try too hard to take off the barrel last time I tried, but I remember it really being on there. I imagine the buffer tube is also.

Now I don't want to sound too arrogant. But I'm a firm believer in fixing ones own problems, especially where one's firearms are concerned. That said, I have a pretty good idea on what to do and won't take it to a gunsmith unless I absolutely have to.

Would anyone of you be so kind as to point me to a helpful book and video dealing with ar upper replacements and so forth? I can usually find what I need for my other firearms but being the AR is the most popular rifle in America I'd like some help sifting through the BS.

Thank you all again for the input. I'll be ordering a new upper soon.

And yes, it's a stag M8l, and I love it so.

 

[Destructo6]

Go over to AR15.com and check out the building/barreling sections and threads. Together, they will explain, exactly, how to pull and install the barrel.

You will need some tools, or access to them for an hour: barrel wrench and receiver vise. Don't start without those two.

With these two tools, and a handfull of other common tools, barrel replacement is comically easy. Without them, you'd might as well not start.

 

[Virg1L]

1 down 1 to go

Have a barrel wrench, now just need the receiver vice. On to AR15.

 

[nyc71]

I would order the first choice given of the vise blocks. I used the "half" upper receiver block & it cracked in the same spot were yours did with an overly tight barrel nut. I first choice completely secures the upper receiver in the vise. Here's a pic of the before (I had to repaint the upper receiver OD green) before and after.
It looks different now with a different stock, longer handguard, & and scope.

 

[mljdeckard]

Don't worry about it. You were smart enough to ask. The beauty of ARs is that any rookie can build or rebuild one. But the upper and lower have to be good.

 

[Virg1L]

Excellent.

Alright. Haven't ordered the upper itself yet, however I will soon have everything needed to replace it once it arrives. Ordered the vice block recommended by nyc, should be here in a few days. In a bit of luck, I hopped on craigslist just to see what was in my area, an hour later walked in the door with a $1000+ Columbian vice from hell and $90 lighter. Turned into a good day to say the least.

Nyc, first off, thanks for the recommendation. I like your larout and am curious about the specs on that glass you have on it. Those stress marks in your first pic was really what hoisted the red flag on my upper. Looks almost identical.

Thanks again to all of you for the help. I really do appreciate it.

 

[dprice3844444]

it's a non stress area,don't worry about it.the only thing you have to worry about is bolt carrier alignment.that's the only thing that matters.the stress is in the barrell and bolt face.the aluminum only keeps it inline.the tight spot will wear in eventually.if you want,replace it.check the buttstock tube for any unusual inside wear patterns.

 

[nyc71]

Alright. Haven't ordered the upper itself yet, however I will soon have everything needed to replace it once it arrives. Ordered the vice block recommended by nyc, should be here in a few days. In a bit of luck, I hopped on craigslist just to see what was in my area, an hour later walked in the door with a $1000+ Columbian vice from hell and $90 lighter. Turned into a good day to say the least.

Nyc, first off, thanks for the recommendation. I like your larout and am curious about the specs on that glass you have on it. Those stress marks in your first pic was really what hoisted the red flag on my upper. Looks almost identical.

Thanks again to all of you for the help. I really do appreciate it.

You welcome, the glass is a Millet 1-4.
I cracked the receiver not "stressed",
here's a better pic of it before I tried to "realign" the receiver.
I recently changed the glass to a MTAC. I'll post a pic tomorrow.

 

[pseudonymity]

I recently used the DPMS Panther claw (second Brownells link) to build a lefty Stag upper. Worked like a charm - it fits pretty securely into both the charging handle slot on the top side and the pins lock the upper onto the claw.

I had to go probably about 2/3 of a tooth on the barrel nut, so I was probably 60+ ft-lbs of torque on the nut, and the upper held with no slipping and no marks at all on the upper. Since the lower part of the claw is clamped into the vice it allows you to use a smaller vice than a clamshell design also.