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Posted: 11/11/2016 10:11:10 PM EDT
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I don't know if this has been addressed but a lot of people are always asking about an AR-10/LR-308 upper receiver lapping tool and I found a company that sells one. It says AR-15 in the link but it is for an AR-10/LR-308. I ordered one. I hope I'm not breaking any forum rules by posting the Link below.
Here's the link: http://pacifictoolandgauge.com/ar-tools/10318-ar-15-upper-receiver-lapping-tool.html |
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If you use a tool like this without having used one before, and you attempt it yourself, you will likely ruin the square face of the lower, and introduce problems where there aren't any.
Gunsmiths just shake their heads when they see the general public with stuff like this. |
| BS. Only a complete idiot could mess up an upper receiver using these tools. I have used them on over 50 uppers and in every case, the process turned out perfectly. Sights zero at or near the mid-range and barrel nuts time with ease. I have used drill presses as well as a hand drill, both with equally perfect results. If one has a third grade education and can read and follow the instructions they are not going to mess up anything, and they are going to square up a receiver that is more than likely not square to begin with. I have yet to find a receiver that was square from the get-go, from the old VLTOR billet, then forged, to DPMS forged, all have been out some. Billet or forged, no matter how close they might have been when machined, the anodizing, or something, has always left them out of square that benefited from being touched up with the lapping tool. |
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Quoted: BS. Only a complete idiot could mess up an upper receiver using these tools. I have used them on over 50 uppers and in every case, the process turned out perfectly. Sights zero at or near the mid-range and barrel nuts time with ease. I have used drill presses as well as a hand drill, both with equally perfect results. If one has a third grade education and can read and follow the instructions they are not going to mess up anything, and they are going to square up a receiver that is more than likely not square to begin with. I have yet to find a receiver that was square from the get-go, from the old VLTOR billet, then forged, to DPMS forged, all have been out some. Billet or forged, no matter how close they might have been when machined, the anodizing, or something, has always left them out of square that benefited from being touched up with the lapping tool. |
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Quoted:
BS. Only a complete idiot could mess up an upper receiver using these tools. I have used them on over 50 uppers and in every case, the process turned out perfectly. Sights zero at or near the mid-range and barrel nuts time with ease. I have used drill presses as well as a hand drill, both with equally perfect results. If one has a third grade education and can read and follow the instructions they are not going to mess up anything, and they are going to square up a receiver that is more than likely not square to begin with. I have yet to find a receiver that was square from the get-go, from the old VLTOR billet, then forged, to DPMS forged, all have been out some. Billet or forged, no matter how close they might have been when machined, the anodizing, or something, has always left them out of square that benefited from being touched up with the lapping tool. I assume you were checking them on a quality CMM before and after, such as a Zeiss Contura G2 series or the likes? I have seen these silly tools take material off of one side of a 2A Upper that was known to be square within 2 tenths. I don't care how precise your spinning hand drill is, it is not as precise as a 400mm pallet in a 20,000 lb Makino A51NX. All I am conveying is be careful with what you might think you are "Fixing." |
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Ok,
I figured I would go ahead and model what I am getting at in Solidworks so people understand what these tools are doing. I often see people say stuff like "It did take some material off one side, so it must be out!!!" It will look like this after you run the tool in your upper. Picture as found on internet! Notice how material is gone off one side to start??? Why would that be? Is it because the face is not square with the bore? NO! It's because your squaring tool is not square to begin with. 
Here I have created a model of an upper receiver bore that is dead nuts square. The extension bore is at 1.000" for 1.25" Depth, most uppers are around 1.000 + .002/-.000 The rest of the bore (Where the tool, and your carrier ride in) is often around 1.005 or so. This means that your squaring tool must be at least .999 to even get inside the upper! Most likely it's around .995 or so in order to turn with the drill. I have my modeled lapping tool inserted in the mock upper. 
Next I set the back of the lapping tool (The part riding on the bore) tangent to the bore at its extreme. I then set the tool tangent towards the front to its extreme. This would model the tool exactly as it would fall if you were to apply any sort of force on the device. If the tool is able to go through the extension bore, then it has room to FALL into the larger bore where your carrier rides. You can see the tool setting crooked in the mock upper receiver here! 
Now lets see what we can see at the front, or the "Face" of our receiver in relation to our tool????? 
What you see is a tiny gap at the bottom where the tool is off of the face of the receiver. If you were to spin this with a drill, it would remove material on one side only! just like the picture I posted above. If you were to keep going, eventually it would remove enough material to make your new upper "Lapped in" and it would be 100% now out of square with the bore. |
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It's good to be square.
In my experience, buying quality parts practically eliminates any need to further square the upper. Quality mfgs already do this, and ship squared uppers. Only the cheapo units need further work by the end user. You get what you pay for. |
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