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Posted: 12/29/2009 11:49:10 AM EDT
[#1]
I can't say how it affects accuracy since I did mine before I shot it for the first time. I prefer to think of it as how can it hurt?
I'm not quite sure who to blame in my build, the Troy rail, BCM upper, Troy sights, or facing the reciever, but when I went to sight in, it required zero windage change, and one click of elevation which I attribute to the top of the Troy rail being just a fuzz taller than the reciever rail. |
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Posted: 12/29/2009 12:02:37 PM EDT
[#2]
Sorry for my ignorance on lapping an upper, but I assume you need to be very careful about removing just the anodizing otherwise you can screw up the headspacing and feed ramp alignments, no?
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Posted: 12/29/2009 12:15:29 PM EDT
[#3]
Quoted:
Sorry for my ignorance on lapping an upper, but I assume you need to be very careful about removing just the anodizing otherwise you can screw up the headspacing and feed ramp alignments, no? Headspace is not a problem, as it is defined by the barrel/extension/bolt relationship. I'm intending to use regular rifle feed ramps (no M4 ramp nonsense for me), so this also should not be an issue. I just want to know if this is a useless fad (a worthless AR15 accessory ? shock, horror  ) or something of measurable value.
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Posted: 12/29/2009 12:15:54 PM EDT
[#4]
they could have an effect, and you only remove enough material to make a face cut on the reciever, very little is taken off, but if someone went wild the receiver extension could protrude too far into the receiver
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Posted: 12/29/2009 12:22:44 PM EDT
[#5]
Quoted:
Headspace is not a problem, as it is defined by the barrel/extension/bolt relationship. Durrrr...I knew I would ask a stupid question ;) |
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Posted: 12/29/2009 12:43:27 PM EDT
[#6]
I don't see how it wouldn't affect the headspacing, if you cut too much off the receiver the barrel would go too far into the receiver, allowing the BCG to travel further into the barrel extension. If there is any extra room, I'm still learning though so that's my thought.
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Posted: 12/29/2009 12:58:31 PM EDT
[#7]
Quoted:
I don't see how it wouldn't affect the headspacing, if you cut too much off the receiver the barrel would go too far into the receiver, allowing the BCG to travel further into the barrel extension. If there is any extra room, I'm still learning though so that's my thought. No, the bolt mates with the barrel extension to set headspace... thats the beauty of the AR system over other, older designs. |
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Posted: 12/29/2009 1:01:01 PM EDT
[#8]
Quoted:
they could have an effect, and you only remove enough material to make a face cut on the reciever, very little is taken off, but if someone went wild the receiver extension could protrude too far into the receiver Any idea how much ? 0.5MOA ? 1MOA ? |
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Posted: 12/29/2009 1:04:27 PM EDT
[#9]
Quoted:
I don't see how it wouldn't affect the headspacing, if you cut too much off the receiver the barrel would go too far into the receiver, allowing the BCG to travel further into the barrel extension. If there is any extra room, I'm still learning though so that's my thought. You need to learn how the bolt/barrel/barrel extension in an AR works. Upper receiver is irrelevant to headspace. |
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Posted: 12/29/2009 1:06:44 PM EDT
[#10]
Quoted:
I don't see how it wouldn't affect the headspacing, if you cut too much off the receiver the barrel would go too far into the receiver, allowing the BCG to travel further into the barrel extension. If there is any extra room, I'm still learning though so that's my thought. With all due respect... The bolt carrier doesn't go into the extension, only the bolt does. The carrier cannot physically fit in there. Now, with regard to the OP. Lapping the face of the receiver essentially squares everything up. One could, in theory, get to butt wild with the lapping tool, but only if lapping beer (a lot of beer) at the same time as using the lapping tool. Lapping the receiver face will typically address those "I adjusted my windage all the way to the left and still shooting right" complaints. I've found it to be a good practice, even with the higher quality uppers. As someone stated above, lapping gets you closer to zero without adjusting anything. As for MOA accuracy improvement, I don't have any data to prove one way or the other except for the two deer I knocked down last week with my latest build. It's fun to pull up to your buddies with two deer on the four-wheeler.
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Posted: 12/29/2009 1:43:04 PM EDT
[#11]
Quoted:
...Lapping the receiver face will typically address those "I adjusted my windage all the way to the left and still shooting right" complaints. Hmmm, my experience is that the sight alignment issue is more a matter of front sight base orientation with irons, and is easily fixed by peening the barrel pin slot to center the FSB. My concern with cutting back the face of the receiver is that it will cut through the anodizing and into the soft aluminum of the receiver, which in my estimation is a bad idea unless there is clear evidence of a benefit. I am really hoping someone has already done a "before and after" accuracy test to confirm a measurable improvement. If nobody can present this kind of data, maybe I should build the rifle first without lapping and see if I have any accuracy problems. |
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Posted: 12/29/2009 1:57:35 PM EDT
[#12]
Hundreds of rifles are built every day without this step and function fine, some even extremely accurately.Accuracy has much more to do with barrels,ammo,shooter than this lapping ever will.Yes, you MAY end up with a slightly better centered barrel, but as long as the nut is properly tightened ( as opposed to under tightened) this will not make it more accurate/shoot smaller groups.And it has the potential to do harm if done incorrectly, my belief is that this goes along with barrel 'break in".If you really think it helps, it will to you.
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Posted: 12/29/2009 2:01:01 PM EDT
[#13]
There really is no concern with going through the anodizing in this location as it is not a wear point.
Aluminum is crazy stuff, even if left completely bare, in about 6-8 hours it will build up a layer of oxidation a couple microns thick that stop further corrosion. This natural layer is both harder, and melts at some 500 degrees higher than the aluminum itself which is why cleaning aluminum before welding is so important. Basically, don't sweat it. |
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Posted: 12/29/2009 2:14:22 PM EDT
[#14]
Quoted:
There really is no concern with going through the anodizing in this location as it is not a wear point. Aluminum is crazy stuff, even if left completely bare, in about 6-8 hours it will build up a layer of oxidation a couple microns thick that stop further corrosion. This natural layer is both harder, and melts at some 500 degrees higher than the aluminum itself which is why cleaning aluminum before welding is so important. Basically, don't sweat it. Yeah, but my concern is whether the hard steel barrel shoulder could start beating its way back into the soft aluminum - after all, the barrel and bolt remain locked until the bullet leaves the barrel, so the full impact of the recoil impulse is born first and foremost in this location  .
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Posted: 12/29/2009 2:29:46 PM EDT
[#15]
Quoted:
Quoted:
There really is no concern with going through the anodizing in this location as it is not a wear point. Aluminum is crazy stuff, even if left completely bare, in about 6-8 hours it will build up a layer of oxidation a couple microns thick that stop further corrosion. This natural layer is both harder, and melts at some 500 degrees higher than the aluminum itself which is why cleaning aluminum before welding is so important. Basically, don't sweat it. Yeah, but my concern is whether the hard steel barrel shoulder could start beating its way back into the soft aluminum - after all, the barrel and bolt remain locked until the bullet leaves the barrel, so the full impact of the recoil impulse is born first and foremost in this location .IF the barrel had some clearance so that it could move in the barrel nut it would start battering the reciever. Since the torque on the barrel nut clamps the two surfaces together, there is no movement, and no battering. Anodizing does not add structural rigidity to the reciever, so if battering could take place, it would happen wether there was anodizing there or not. Think of anodizing like the paint on the fender of your car, it protects the metal from corrosion, and makes it look better, but it's not going to stop every scratch, and it definatly won't stop dents. The connection between your shoulder and the stock is going to take more of a battering than the connection between the barrel and reciever does when you fire it. |
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Posted: 12/29/2009 2:58:34 PM EDT
[#16]
OK, that makes sense - thanks.
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Posted: 12/29/2009 3:22:34 PM EDT
[#17]
No problem.
There are lots of opinions here based on opinions that have no thoughts given to the actual properties of the materials in question. Another one is "don't polish the trigger, you'll go through the surface hardening and it'll wear out". Yet if you look at a trigger, the sear surface is clean machined material, so it was obviously done after coating. The coating will not survive the hardening process, so it was machined after hardeing. That being the case, polishing isn't going to go through the hardening since it was machined off after the part was painted, if it was even hardened to begin with. Things that make you go HMMMMMM. |
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Posted: 12/29/2009 4:11:23 PM EDT
[#18]
I did'nt "face off" my Mega upper reciever and my Troy rear sight only needed 3 clicks of windage, but I attribute that to the sights' fitment on the rail.
Just my 2cents. |
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Posted: 12/29/2009 5:05:42 PM EDT
[#19]
Quoted:
Quoted:
...Lapping the receiver face will typically address those "I adjusted my windage all the way to the left and still shooting right" complaints. Hmmm, my experience is that the sight alignment issue is more a matter of front sight base orientation with irons, and is easily fixed by peening the barrel pin slot to center the FSB. My concern with cutting back the face of the receiver is that it will cut through the anodizing and into the soft aluminum of the receiver, which in my estimation is a bad idea unless there is clear evidence of a benefit. I am really hoping someone has already done a "before and after" accuracy test to confirm a measurable improvement. If nobody can present this kind of data, maybe I should build the rifle first without lapping and see if I have any accuracy problems. Good idea. Do a before and after. Never seen evidence of the smack the barrel back into alignment, or heard of it anywhere but here. A hammer mechanic can address the problem but not the issue. I'll continue to lap the upper. 458 |
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Posted: 12/29/2009 6:06:50 PM EDT
[#20]
I have found that most of the time, the problem is that the FSB and the index pin are not in perfect alignment with each other. Poorly made, improperly used, or loose tolerance jigs for drilling the taper pins on the FSB are most likely the culprit. The wack with a hammer technique(this came from Bushmaster btw) is a bunch of shit if you ask me. It probably just drives the index pin where it doesn't belong. If you notice when the extension slides into the notch on the upper, there is maybe a few thousands of an inch of play, probably not enough to move the rear windage one click(note I did not do the math on that, correct me if im wrong). Another culprit could be that the picatinny rail on the top of the upper is not true to the bore of upper.
It is this reason, the DCM FSBs exist. So you can zero the shit out your sights in a wind free envirment and not worry about the rear windage being off one little bit. At first I thought the lapping idea was a good one. I tried it. It didnt do anything except remove the finish from the end of the upper and cost me like $30. Removing anodizing on aluminum is no big deal. Its just a surface treatment. If it worries you, touch it up with Aluminum Black. |
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Posted: 12/29/2009 7:48:05 PM EDT
[#21]
Glad the hammer thing is working out for you.
I'll stick with the basics. 458 |
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Posted: 12/29/2009 11:02:17 PM EDT
[#22]
Yeah, I don't like the "whack the FSB" solution either... when I had this problem, I removed the barrel nut, filed on the barrel pin slot of the upper with a needle file to get the FSB straight, then used a hammer and punch to peen the other side of the slot to hold the correct orientation. Of course, this is only an issue with iron sights and not related to my original question about facing the receiver. For the record, the build in question will not have iron sights.
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Posted: 12/30/2009 5:39:09 AM EDT
[#23]
A quality machined upper should not need any facing to make it true. Removing the bbl. and then replacing it may change its orientation slightly no matter what is done to the receiver.
Too many factors to contend with trying to do a comparison. |
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Posted: 12/30/2009 6:06:49 AM EDT
[#24]
I dont know about trueing up an AR upper. But one of the first thing a gunsmith does to a bolt gun is true up the reciever,
If the upper is not true, then the barrel (when tightened ) will flex the reciever. When fired the rearward motion from recoil should cause the barrel to move in the direction of least resistance. If it's enough that it moves different each time that should cause slightly different points of impact. Will you be able to notice the difference ? I dont know how slight it will be. It should take out one of the many variables tho. It does sound like a good project tho. |
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Posted: 12/30/2009 8:50:27 AM EDT
[#25]
There seems to be a misconception here about lapping the receiver to fix canted fsb. It won't happen. What lapping the receiver does is makes sure the face is perpendicular to the bore of the receiver and making sure you have at least 80% good contact with the barrel's extention flange to the receiver face. If you've ever installed a ff hg and noticed the barrel is closer to one side than the other, this could be from an unsquare receiver face. There are quite afew builders out there that check the uppers quite extensively for this, I know D-tech and MSTN does.
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Posted: 12/30/2009 4:13:23 PM EDT
[#26]
I've read of instances of rifles that refused to shoot straight magically healing themselves after the owners lapped the receiver. The physics of it support the process, and mass production being what it is, the individual craftsman will nearly always do a better job than the factory.
That being said, a goodly number of these things get put together and shoot quite well without the lapping. My advice, for the little its worth, is to check the receiver for square, put the thing together and see how it shoots. If results indicate the need, pull it apart and lap the receiver. If you're wondering whether to purchase the tool, that's a different equation. How many are you going to build? How much does the tool cost? is the cost/use ratio something you're willing to endure? If yes, buy one, it couldn't hurt. If no, don't buy one, you may not need it, and if you do, it may be in your interest to either borrow one or have somebody else do the lapping. For myself, I'm gonna buy one of the tools, but use it only when required. |
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