AR Sponsor
Posted: 8/2/2010 3:58:23 PM EDT
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I see references to lapping an ar receiver to increase accuracy. Anyone done this? Is it important? Are there any video's on the process? Brownells seems to have a video for everything but that.
I'm making what I hope is my last midway purchase for my build while I wait on my barrel so I want to buy the tool if I need to. |
| Newbie I have used Brownells receiver lapping tool on 3 different AR's. It is very simple to use and it came with detailed instructions. I used Permatex valve grinding compound coated the body of the tool that slides into the upper with oil and chucked it into a drill and gave it a spin. Checked it until the receiver face was square. I found that I had to use brake cleaner fluidto remove the oil and soap and water to remove valve grinding compound. I have since purchased a jar of 600 grit lapping compound and it removes easier than the valve grinding compound. |
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Quoted:
I see references to lapping an ar receiver to increase accuracy. Anyone done this? Is it important? Are there any video's on the process? Brownells seems to have a video for everything but that. I'm making what I hope is my last midway purchase for my build while I wait on my barrel so I want to buy the tool if I need to. Some upper receivers really need to be lapped while others don't really require it ... depends on the squareness of the uppers face. The way I check the this is I take a 1/2 piece of aluminum plate and stand the upper on its threads facing down then I take my bore light and run it down inside the upper and then I look for light escaping from around the the upper and the plate.If there is alot of light escaping then the upper probably should be lapped. I purchased the tool and have been lapping most all of my uppers. The lapping tool and lapping compounds are sold separately ... there's a cutting, smoothing and polishing compound. Unless the upper is really bad you really don't need to use the "cutting compound" and you can start with the smoothing compound and then go to the polishing compound. This is the one I purchased from Brownells you can use it with any standard drill. And these are the compounds I purchased from Midway. Hope that helps. |
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I have done two dozen uppers, including VLTORs MUR billet upper (and later when they switched to forged) and I have yet to find one that did not need lapping on the face of the threads to square them up. You do not lap inside the receiver normally, just the face of the threads. IMO standing them up tells you nothing (your eye isn't that good), put that lapping tool on them and that will show you damned quick if it is true or not and I have yet to find one that was true from the factory, and that includes two VLTORS, several BCM, RR, several DPMS, two COLTs, three DD, two YHM, one Bushmaster, and quite a few assorted uppers that I do not know who finish machined them and with various forge markings. I have had three that did need lapping of the inside of the receiver in the area of the barrel extension because the tool would not go in, VLTOR forged, one of my three DD, and the RR upper all needed the inside of the barrel extension area lapped so the tool would go in before the squaring of the face could begin, but only in the barrel extension area where the anodizing was a bit too thick. That is the reason I have two tools, one for lapping the inside and one for lapping the front. Once you lap the inside you will embed compound in the body of the tool and that may cause undue lapping in other uppers where they are not undersized and you do not want lapping to occur.
When you hear people complain that their barrel is not centered in the forend or their rear sight must be adjusted all the way left or right or up or down to zero, nine times out of ten it is because the front of the receiver threads are not squared and that forces the barrel to point off in a direction not in line with the axis of the upper receiver. Does it increase accuracy? Logically I'd say yes but I won't swear to it. But I do know it sure as hell won't hurt accuracy any. I also know that if I am going to the trouble and expense of building an upper I am darned sure going to make sure the front of the receiver is square so when I get done I won't have any nasty little surprises when I get the rifle to the range the first time. |
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Quoted:
I have done two dozen uppers, including VLTORs MUR billet upper (and later when they switched to forged) and I have yet to find one that did not need lapping on the face of the threads to square them up. You do not lap inside the receiver normally, just the face of the threads. IMO standing them up tells you nothing (your eye isn't that good), put that lapping tool on them and that will show you damned quick if it is true or not and I have yet to find one that was true from the factory, and that includes two VLTORS, several BCM, RR, several DPMS, two COLTs, three DD, two YHM, one Bushmaster, and quite a few assorted uppers that I do not know who finish machined them and with various forge markings. I have had three that did need lapping of the inside of the receiver in the area of the barrel extension because the tool would not go in, VLTOR forged, one of my three DD, and the RR upper all needed the inside of the barrel extension area lapped so the tool would go in before the squaring of the face could begin, but only in the barrel extension area where the anodizing was a bit too thick. That is the reason I have two tools, one for lapping the inside and one for lapping the front. Once you lap the inside you will embed compound in the body of the tool and that may cause undue lapping in other uppers where they are not undersized and you do not want lapping to occur. When you hear people complain that their barrel is not centered in the forend or their rear sight must be adjusted all the way left or right or up or down to zero, nine times out of ten it is because the front of the receiver threads are not squared and that forces the barrel to point off in a direction not in line with the axis of the upper receiver. Does it increase accuracy? Logically I'd say yes but I won't swear to it. But I do know it sure as hell won't hurt accuracy any. I also know that if I am going to the trouble and expense of building an upper I am darned sure going to make sure the front of the receiver is square so when I get done I won't have any nasty little surprises when I get the rifle to the range the first time. Do you need to apply anything to the bare metal before assembly? |
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