View Full Version : Is this in spec for an upper
ncshooter18
11-11-15, 07:55
I just got a stripped upper for a build and I noticed the left "wall" is thinner than the right one. Is this in spec?
http://i280.photobucket.com/albums/kk179/7lf10/55FAD7A1-7D8A-4D1D-ADDD-C8B996266CC6_zps420ssfqx.jpg (http://s280.photobucket.com/user/7lf10/media/55FAD7A1-7D8A-4D1D-ADDD-C8B996266CC6_zps420ssfqx.jpg.html)
ncshooter18
11-11-15, 09:38
curious... who's upper?
Aero Precision.
FWIW I just got to look at my friend's 6920 upper and it looks like this as well.
It's not unusual to see both upper and lower receivers machined from forgings off center a little bit. Does it hang off of the right side of the lower more than the left?
ncshooter18
11-11-15, 10:03
It's not unusual to see both upper and lower receivers machined from forgings off center a little bit. Does it hang off of the right side of the lower more than the left?
Yes, but my BCM upper does as well, and both "walls" are equal width on the BCM.
ncshooter18
11-11-15, 10:55
Shoot it.....
That would be kind of hard since I don't have a barrel yet;)
titsonritz
11-11-15, 11:45
Aero Precision.
FWIW I just got to look at my friend's 6920 upper and it looks like this as well.
So does mine.
titsonritz
11-11-15, 11:45
Aero Precision.
FWIW I just got to look at my friend's 6920 upper and it looks like this as well.
oops double tap
Since it's a forging, all the "Specs" are internal for the most part. As long as the charging handle latch cut is done correctly I see no issue other than cosmetic.
We have seen forgings with core shift as far as .030 out. We have also seen them with extreme taper from one end to the other.
Ryan
I'll check mine when I get home, but I'd say shoot it. I can't see it giving you any issues.
Since it's a forging, all the "Specs" are internal for the most part. As long as the charging handle latch cut is done correctly I see no issue other than cosmetic.
We have seen forgings with core shift as far as .030 out. We have also seen them with extreme taper from one end to the other.
Ryan
The forging drawing states a maximum mismatch of 0.020"....
Here ya go... I posted this around 2013???
It has some technical info as far as what is seen when machining forgings.
So when you order forgings, they come in large boxes, stacked in layers. Typically you see 400 pieces per large box.
https://lh3.googleusercontent.com/-DCC1bgNyBgI/UhOBLLADd-I/AAAAAAAAAds/5NWGL_kQ2ho/w1280-h853-no/IMG_2974.JPG
Each forging has a "Die Mark" "Strike Mark" whatever you want to call it on the part itself, typically this is on the port door area of the forging. This is why you don't see it after process as that area is removed in machining.
https://lh5.googleusercontent.com/-oH8QLX_zNB4/UhOBLafONlI/AAAAAAAAAd0/UoW4mV61icc/w1280-h853-no/IMG_2975.JPG
Here are examples of what we see as far as blems, or quality issues with the forgings. In this first example, the forging has what I would describe as ripples along with a decent indentation half way down the rail area of the forging. This would be a perfectly functional part, however I would expect someone to question quality based on this. This could also affect fixtureing depending on how a company is holding the forging. In the end, it's a scrap part from a QC standpoint.
https://lh4.googleusercontent.com/-B3WIeRIJjAk/UhOBLObQ_GI/AAAAAAAAAdk/XFRN3Uh2kqc/w1280-h853-no/IMG_2977.JPG
Another MAJOR problem is "Shift" this has been a huge issue in some cases, as we have seen it as far out as .030 in some cases. The two halves that come together to make the strike do not line up, and you end up with one side of the part, higher or lower than the other side. In this example, you can see the center line, and the two halves on both sides shifted top to bottom. One being higher than the other.
https://lh5.googleusercontent.com/-UB5LEhderu0/UhOBM9g89fI/AAAAAAAAAeA/YtKv73EzgZY/w641-h905-no/IMG_2982.JPG
In this example we have a massive indentation in the forging. I am almost wanting to run this forging just to see how thin the wall will be after cutting! Either way, this is a junk forging.
https://lh4.googleusercontent.com/-0eZ4FwCwQ-4/UhOBLyclhJI/AAAAAAAAAdw/gP1G6kXgBS8/w1280-h853-no/IMG_2979.JPG
Another view of same forging:
https://lh5.googleusercontent.com/-yBk7XhUZV2Y/UhOBL_SUNDI/AAAAAAAAAd8/dQTcLMD4TNM/w1280-h853-no/IMG_2980.JPG
All of this is compounded by the fact that these also move during the cutting operation. It can be predicted yes, but each die has it's own characteristic. Probing can line you up on the forging, however compensating for movement in the part itself is a trial and error process, and it changes with each die. If done correctly you end up with a nice part!! But if you start with crap, you end up with crap. right now the forgings are crap. Those steps that you see just below the rail on your upper receiver???? I have examples here that have so much taper in the forging that the step actually fades to a perfect flat on both sides. Sometimes the step is more prominent on one side than the other. Again, this can be tracked right down to the die.
Good part.
https://lh5.googleusercontent.com/-xfzITkOshWE/UeYmKox-VmI/AAAAAAAAAac/cbohfeh2Vms/w1280-h853-no/IMG_2885.JPG
Just checked a few of mine and did not observe a similar issue.
A forged NEA on the left and an Aero Precision on the right.
http://i1052.photobucket.com/albums/s460/Peter_Schiestel/76e3761f29e62b9c74bc648b225475ce_zpsw427vcjh.jpg
A billet MI on the left and a Billet NEA on the right.
http://i1052.photobucket.com/albums/s460/Peter_Schiestel/00f62f8e66e7675e051ca0be7aecccf7_zps49jpj5nj.jpg
Just checked my sample of two.
Palmetto
L=.118"
R=.108"
BCM4
L=.116"
R=.120"
Clarence
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