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Posted: 12/21/2011 1:49:46 PM EDT
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Friend suggested this instead of the lapping tool everyone else talks about:
http://www.brownells.com/.aspx/pid=20449/sku=080-000-195/Product/1-Receiver-Facing-Pilot Stupid question though, but which way is the cutter turned when pressed against the receiver's face? Is it the sloped side or the 90 degree side that turns against the face? Also, I'm assuming that since this is actually cutting rather than lapping, no drill needed - can be done by hand? |
| The edge that is perpendicular to the face of the receiver does the cutting, so you turn it in that direction. Usually it is clockwise. Unless you are doing a whole lot uppers, that is a pretty pricey tool to use for just one or two receivers. While there is no doubt it is a hell of a lot faster to use, it is also a hell of a lot faster to get carried away and remove too much from the face of the upper. In a business I would consider that tool a must have, but for a home do-it-yourselfer, which I am, the lapping tool is plenty fast. I have done two dozen uppers with two lapping tools and the second was bought because I dropped the first one and bent the crap out of the part that goes into the drill motor. If not for that it still works just fine. Never turn it in the direction of the angled surface. The nice thing about the lap is it does not dull or need sharpening. A cutter, if used enough, will eventually dull and if you make it chatter, you can really mess up the mating face of the receiver. |
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Quoted:
but for a home do-it-yourselfer, which I am, the lapping tool is plenty fast. I have done two dozen uppers with two lapping tools and the second was bought because I dropped the first one and bent the crap out of the part that goes into the drill motor. If not for that it still works just fine. Never turn it in the direction of the angled surface. The nice thing about the lap is it does not dull or need sharpening. Any real benifit to using it? I understand the concept is to tru the face of the upper receiver. I'm just wondering if it really makes for a more accurate or more reliable rifle? |
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Quoted:
Any real benifit to using it? I understand the concept is to tru the face of the upper receiver. I'm just wondering if it really makes for a more accurate or more reliable rifle? It can be a huge benefit to some rifles, and virtually zero benefit to others. Sometimes the receiver face can be out enough to cause the barrel to shift out of line one way or another when it's torqued down. This usually results in huge elevation and/or windage adjustments being required to get the rifle zeroed. With the face trued with the barrel, everything just aligns much better. Whether it's worth it or not depends entirely on the rifle and it's individual owner. |
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One real benefit is when the hardcoat isn't even on the front end of the upper, making it difficult to torque the barrel nut accurately. Truing the face of the upper often makes such uppers much easier to get the barrel properly installed.
On a precision build, ensuring the face of the upper is square helps make that expensive barrel line up as perfectly as possible. Otherwise, truing the upper's face really isn't much more than a waste of time. |
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Turing the face well give you better bolt lug fit. The Grendel guys that had bolt lug breakage problems started lapping the face of their uppers and saw a major reduction in lugs breaking. I use the lapping style with fine grit lapping compound. I feel it gives me a finer control. On some uppers you well see the face is already square with the bolt center line. On others you well see it's off when you are through the hard coat on just half the face.
Turing the face of the upper well effect to barrel nut torque needed to reach gas tube alignment. |
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Makers don't do it because it takes time, and the time it takes to square up a receiver can be used to build another upper. Assembly line fashion one can build an upper as quick as one can square an upper receiver, or darned near as quick. Some makers do offer it as an extra though. I know ARP does it for a few bucks more and WOA does it on their match grade uppers, or so I have been told.
As to accuracy, reliability, and longevity, you cannot prove it by me that squaring does anything to improve accuracy or to increase reliability or longevity. I have seen no accuracy increase in mine, and since I have never broken a part or worn out a part or had a chronically malfunctioning rifle, I cannot say it will increase reliability or life. What I can say without a doubt is that squaring will more than likely allow you to zero your sights with them at their midrange of adjustment instead of being maxed out one way or the other. That alone right there is enough for me to do the squaring. I make no other claim other than that. |
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My limited experience has been that some uppers will benefit, some will not.
First Experience - I assembled two uppers with identical parts. One was for me, the other for a buddy. The uppers and barrels were sourced from WOA, KAC FF rails, etc..... everything bought in "2's". After finishing the uppers, I tested them both at the range with the same ammo and optics. The upper that I had identified as mine would group 1 to 1.5 MOA. I was a little disappointed. My friends upper would group .5 to .75 MOA. It was like a laser. I started to swap them out because he wanted a nice AR. He is not sick with BRD like I am. However, I didn't do that, I did the right thing. Anyway, a year or so later I started to want my MK12 to be more "spec" so I took everything apart and reassembled the upper with a different forearm. The same barrel, upper, and bcg were used. By this time in my home wrenching I had begun ussing the lapping tool because the theory seemed sound. When I reassembled the components the results were greatly improved. That rifle will now shoot .75 MOA if I do my part. This isn't conclusive; however, it is an indicator. Of course it could just be taking it apart and putting it back together helped. Second Experience - I have a RRA upper which has never grouped the way I like. The best I could ever get out ot the rifle was 2 - 2.5 MOA. The groups were strung vertically. So, based upon my research when doing my 6.5 Grendel builds led me to "bed" the gas block. This offered no improvement. In frustration, I tore apart this factory built upper in order to reassemble it "my way". This upper was the most out of square I have yet seen. I really wish I had taken it to work and made some measurements of the reciever front plane to the ID of the upper where the barrel extension seats. I any event, I've now had that rifle back to the range only once. It did 1 - 1.25 MOA groups. Not a laser, but not a slob either. I was in a hurry and shooting off my RCBS RASS. The RCBS RASS is great for a quick set-up place to shoot from, it is NOT a replacement for getting behind a bench. So the upper appears to be performing better. The only changes were the disassemble / reassembly and the use of the lapping tool. It appears, these two uppers benefited from the use of the tool. However, this is a very limited sample. In any event, I will continue to use the tool. R4B |
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Quoted:
Using a lapping tool also can help if you're having trouble getting the barrel nut torqued that last little bit to get the gas tube hole lined up. +1 on this. Lapping just a few thousandths of an inch will give you another 1/2 a tooth when torquing the barrel nut. |
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