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Posted: 12/19/2015 4:09:05 PM EDT
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I recently got a lower that has (imho) a significant difference in wall thickness in the receiver trigger well. .094 on the left vs .069 on the right.
It was won off gunbroker NOS but vendor states warranties handled through manuf.  wondering if these are blems that aren't described as such?
anybody seen such a difference in thickness and would it cause a problem down the road with say, pins oblonging holes? |
| You can always contact the manufacturer and see if they will warranty it. Ideally both side walls would be nearly equal, casting or machining issues may have caused the slight offset. Since the lower is forged and hardcoat anodized ( ? ) , the trigger group pin holes should wear the same as any other lower. It is not like the trigger group pins are under a great deal of stress. |
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The with in that area is .87 +/- .010 inch, so it can be as wide as .88 or as narrow as .86.
The pocket is .690 +/- .005 inch, so it can be as wide as .695 and as narrow as .685. The tolerance on the pocket to the centerline of the forging is +/- .005 inch. A maximum width pocket (.695") in a minimum width forging (.86") off center the maximum amount would be .0775" on one side and .0875" on the other. However, there is also a parallelism tolerance on the forging that states the sides of the .86 area can be up to 0.020 inch off parallel to the overall forging centerline over the entire length of the .86 area. Up shot - The right inside surface of the trigger pocket should be .095 +/- .003" from the inside surface of the right pivot lug and the forward and aft portions of the inside right magazine well are .198 +/- .004" from the inside surface of the right pivot lug. As long as those are right, the outside doesn't matter that much |
| This is the reason that I went to billet. As a small production shop,when I would buy 500 forgings at a time (that is the minimum the forging companies will go for a decent price) I would be lucky to get 200 that were at least minimum spec. When you set up your x-y axis for center line, If you do not batch your receivers in .005 thickness variation, and change the center line accordingly, this is what you end up with. In mass production where some one is just loading the tombstones, The machine does not know the difference. After Sandy Hook, the forgings were horrible, at least the ones I received were. I think that the forging companies send out to us small guys, all the culls that the big guys will not accept. I engrave all my markings so that is another area that causes a problem also. I can buy a hundred feet of billet and get it delivered free in less than a week, any time. Craig |
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