Is  to it worth to lap your upper receiver before installing your barrel?  I was going to order a lapping tool but thought I'd ask to see if anyone has done this and was it worth it. MC

No.

Message too short..

No.

I haven't done this because I've never had an upper that was off-true enough to be a problem.  IF you were building a VERY HIGH precision upper, AND you were using an EXTREMELY high precision barrel, it might help...but you'd be using an extremely high precision upper that should be held to such fine tolerances that you wouldn't get anything better from lapping that very expensive upper.

If you had a problem getting a decent torque level after several tries, AND you found that the face of the upper was uneven or inconsistent, then lapping the face of the upper would be quite useful.  Otherwise, it's not going to get you a whole lot of improvement in anything.

Depends on the build. If you're going to try and assemble the a high dollar rifle to punch small holes in paper, then i can't say no. If you're looking for a plinker i also won't always so no. I had a fortis upper i got that was pretty bad off and i had to damn near max out my windage on my rear sight to zero it (yes assembled correctly, propper torque and tried multiple barrels). Lapped it and brought it back to center with no issues. My vltors come perfect straight from the factory, so for those its unneeded, but i have had several different uppers benefit from it.

Thanks for the replies folks.  I'm using a Aero precision upper and lower for this build. I feel that Aero is a good quality upper  and should be square from the factory. I got to reading about lapping the upper and this was the reason I asked if it would be worth it to spend the money for the lapping tool and compound. Think I will go ahead and assemble the upper, shoot it and go from there. MC

Not needed.

Not needed.

You can check and see how much contact there is between the BE and the face of the upper.
In a bad case you can wind up with the bore of the barrel not in line with the center line of the upper.
I tend to think bad cases are few and far between.

Waste of time and effort that should be used elsewhere.

Vince

Thank you  all for your replies. From what all of you said that it wasn't worth it I did not order the lapping tool. I did order a Vortex flash hider and a Gas Buster charging handle .

if you can do it for free like i did, why not?
does it do anything? no.

did it hurt anything? no.

it did take roughly 5 back and forth motions by hand to get the Dykem off all the way around.
yippee

If a barrel nut can not be timed properly, lapping the face can help. Been there done that.

OK I have a feeling that most of the "waste of time" responses you got were from people that have never used the tool or really grasp what it does for you.  I personally lap every upper I get my hands on.  The tool isn't that expensive and the process is pretty darn easy for the results you get.  

What it does for you... it trues the face of the upper to the barrel extension flange.  If the face is out even a few thousandths it won't affect function, but the longer your barrel is the more the imprefection is magnified, creating a condition where the barrel is not in allignment with the upper.  This can mean you have to make big adjustments to your sights/scope/red dot to accomodate this imperfection, and there are cases, however rare, that folks have run out of adjustment and were forced to lap anyway to correct the problem.  The lapping centers the bore exactly in line with the upper and minimizes the need to make sight adjustments.  As someone else mentioned it can also help if your barrel nut just doesn't line up when torqued.  By lapping the face down a hair you can get just a little more twist before bottoming out and allow proper timing of the nut.

After some 20 uppers I've lapped for myself and friends there wasn't a 1 that was perfect and didn't benefit from it.  With the face being trued the pressure applied to the barrel extension flange is even and square and therefore the torque applied is even all the way around the flange.  If there are peaks or valleys in the face of the upper this creates an uneven clamping force and can induce forces that cause a reduction in accuracy of the barrel.  You will NEVER see a bench rest guy without a lapped upper.

As an added benefit (for me at least) I use the tool to polish the inside of the upper as well.  It follows the path of the BCG and smooths the surfaces that the BCG contact.  My ARs are buttery smooth from the moment they go together because of this.

So ultimately do you have to do it?  Not at all.  Your AR will function just fine.  If you're spending money on a good barrel that you intend to free float and have a good trigger behind you obviously care about accuracy, and you may very well be leaving accuracy on the table by not lapping the upper.

If the BRD takes hold you'll never wear the thing out and you can use it on every build you do.  For the price vs potential benefit why not do it?

Since nobody has presented any before/after accuracy comparisons, there is no way to say it helps and/or that it doesn't hurt.  You say of your experience with uppers that you've seen "1 that was perfect and didn't benefit from it."  HOW did it benefit and how did you measure that?  Just because those other 19 uppers were not precisely true and you made them so does not mean that there would have been a detectable difference in accuracy if you had not lapped them.  Suggesting that "you may very well be leaving accuracy on the table by not lapping the upper" has no evidence behind it.  I'd really like to see some comparative accuracy results (including how the sights lined up) with the same barrel and upper without lapping and then with lapping.  I'm not saying there's no benefit, but nobody has demonstrated that benefit yet.

If the barrel nut doesn't time because the upper's face is irregular, or if the barrel won't zero because it's at an angle, those are really obvious reasons to do it.  If one has a heavy hand, of if one doesn't understand that the upper lapping tool is a HAND tool, they can wind up with a damaged upper just because they think "it can't hurt."  The design of the AR is such that it can absorb a lot of tolerance stacking before things don't work well, including having microscopic irregularities in the face of the upper.  So I don't think it's "a waste of time" in some circumstances, but I also don't think it's necessary or even appropriate most of the time.  They're your uppers, do as you want, but the potential improvement (still theoretical since nobody has any data to present) is very small.  This is not something that should be done all the time, nor be needed all the time, or precisely true upper receiver faces would be THE standard, and that isn't the case.

Nobody has done this  because it's an unreasonable experiment to carry out.  It isn't enough to shoot the rifle, disassemble, lap, then reassemble, and compare.  There are a number of both systematic and random error sources during a build that when propagated could create error bars that eclipse the relatively small differences in "perceived" accuracy.  Furthermore I use the word 'perceived' because there are also environmental factors separate from the build issues that will have a non-neglible effect on the ballistic trajectories of both experiments being carried out.  

Assuming you could perform these tests in either a vacuum or an environmental chamber, a proper experiment to test this lapping hypothesis would require the individual to assemble MANY upper receivers, normalize and average MANY shots, then lap the uppers, and again normalize and average MANY shots.  Only then could you build a statistically significant data set to start analyzing and drawing conclusions.  A very time consuming and expensive proposal.

I will gladly start accepting donations to get started

The only thing lapping will do is nothing.

I'd rather waste the money, I saved from not buying that stupid tool, on a "lap" dance. YMMV.

You make the point that there is no data can be referenced, yet everything you add is conjecture of your own.  There is a reason the BR guys ALWAYS do it, and I trust them about accuracy more than one that does not compete in it. To that end if it were actually damaging something the BR folks would probably NOT be doing it because of the potential to screw up a custom piece. If you want to explain to me how making something perfect that isn't is bad I'm willing to listen, but if you've never built things to beyond what is necessary and ventured into the world of "above and beyond" then this probably isn't your bailiwick.  As for "proof" here's an article for you to take a look at.  If you want specifics about the lapping see the bottom of page 2 and into page 3 where the author specifically addresses lapping uppers and his benefits noted.

http://www.longrangehunting.com/articles/building-accurate-ar-15-1.php

For the record you would have to put effort into messing the job up as the compound is taking material off by for less than thousandths of an inch (that's less than .001in).  I use 600 grit, which is typically the final grit of sandpaper used when applying a professional paint job to a vehicle.  Finer still is where you are getting into wet polishing for your show car.  In other words its VERY LITTLE, so the material removed is equally very little.  The tool comes with directions as well and if one can't grasp them in their simplicity then they probably should not be handling firearms in the first place, and certainly could not complete a build.

Another point... the tool specifically is NOT a hand tool.  It is designed to be put into a drill and used with power as specified in the instructions.  The drill applies the power to rotate the tool within the upper while making contact with the face of the upper.  The upper itself serves as the guide that the face is squared to.  This is similar to balancing and blueprinting an engine.  You can build an engine that will run just fine without it, or you can put extra effort into making as many things as possible perfect to maximize performance and minimize potential problems.  I want my stuff perfect and want to PREVENT issues rather than treat them after the fact.  If you want to put something together to FIND OUT if it will be ok then more power to you, but if it's not you're pulling it back apart to correct something.  It takes about 2 minutes to do the average upper, and that's a lot less than it takes to take one back apart because it turns out it really needed it.  I know that I will not have a problem with the barrel not being square to the upper as I've eliminated that as a possibility; an ounce of prevention truly is worth a pound of cure. Again, 'splain to me how that's bad Willis.

So, like I said before, you can buld a perfectly functional piece without doing it, but there certainly is no down side to doing either, and frankly using fear of screwing something up as a reason to not do it is akin to gun control folks using fear as a means to limit our 2A freedoms.  If you think this way about everything you wouldn't even try to build an AR, ride a bike, ask for a date, drive a car, get a job, have kids, etc.  

So long as you follow directions and rules there is no reason to not lap an upper.  Determining if it's important to you is what matters, and it is to me.

my .02

I am a machinist so I lapped both the builds I just did (tool was free and sent to a buddy)

my wife's build and mine

both uppers were RT bare (cerakoted mine and baked rustoleumed here's) , marked both with dykem and trued up, honestly maybe took off a .003/.005 burr from thread lead in, painted both, and assembled both with Delton 16" barrels

I sighted my PA 1-4 scope first on mine, she liked it and I swapped it onto her rifle...NO adjustments were needed at 50 yard zero...NONE

was it because I lapped them both? I don't know, quality parts were used and both nuts torqued at 39/40 pounds (also greased upper threads)

So for me it was worth what little time it took, I also was anal and checked lowers with pins to the old colt prints was bored one night

It's about learning and having fun

So like has been said you can do it or not

Since my conjecture is equally as valid as yours, it looks as if we're at an impasse.  I have no evidence it's bad, and you have no evidence it's good. BUT I'm not saying "don't do it!!!" while you're saying "it helps," as if you did have data.  Sure, it's unlikely you could hurt anything, but evidence is crucial to saying "it's OK," and equally as crucial to saying "it helps."

As for "hand tool," yes Brownells' instructions tell you how to use it with a drill, but it needs to be used AS a hand tool, instead of ramming the tool against the face of the upper and setting the  drill to "supersonic."  How many times have you seen someone post that "after doing X that I read about here, my gun is broken..." and it turns out that they figured "if a little is good, a whole lot must be great!"?  So when I said it's a "hand tool" I meant it needed to be used carefully and maybe even "gently" rather than with a pneumatic concrete drill...  No I don't have much faith that everyone will be careful or even attentive when doing something like this.  I have too much experience with "user induced failures" in all sorts of stuff to trust anyone to be careful unless I have made sure they will be.

It's not unreasonable to insist on evidence for stating something "helps all the time."  It's a tool that can, in careful hands, produce a change of a few thousandths of an inch in the surface of the upper's face, which might be useful in some situations.  I mentioned the lack of data because of a post that says (paraphrased) "it helps in 95% of my uppers" without any data to back that up.  Lapping an upper's face might be great if you can't get two or three different barrel nuts to time, or if once you got the barrel on it was measurably off center.  But the poster I replied to says it helps essentially EVERY gun, even though he cannot know that, not having even tried to test his statement.

The testing I suggest doesn't have to be anywhere near as involved as you mention.  It could be as simple as assembling an upper without lapping, firing a few hundred rounds through it in a machine rest, and then taking it apart and lapping the upper before reassembling it and repeating the firing tests.  If any measurable improvement in accuracy (not POI vs. POA, but grouping regardless of POA) were seen, it would suggest repeating the test with at least two more uppers.  If there were negligible or no changes in accuracy, that would say that either the testing was flawed, or that there were no generalized accuracy benefits from lapping EVERY upper before assembling it.  I'll note that in my armorer class, the instructor showed us how to do a quick check for trueness of the upper's face.  You clean it off and try to balance it by sitting it on the face on a flat, level surface (he used a vise anvil).  That is the level of true necessary to build a consistent rifle.  Not necessarily the desired level of trueness, but "enough" for a rifle that will shoot as accurately as the barrel allows - even if you have to adjust the sights all the way to one side to sight it in.

[popcorn]

I do this to everyone of my receivers.  Main benefit I have found is being able to swap optics between uppers with very little POI change.  I have nice 1-6x24 scope that I cannot afford to have placed on each of my rifles.  So I swap the optic between my uppers as needed.  

I have found that all of the uppers I have used the lapping tool on are not square from the get go.  I have used this tool on BCM, VLTOR, and Mega Uppers.  

By squaring the face you are also allowing your bolt lugs to have equal pressure applied to them during firing.  In the case of my 6.5 grendel this prevents broken locking lugs that are more common in this caliber than 5.56.  

It only adds about 5-10 minutes to the assembly time.  It makes sense to me that having a barrel that is straight and true when mounted in the receiver can only be a benefit.  

This is just my 2 cents on the subject.  

Edit: I remembered a post by Big-Bore (ADCO) convinced me to lap my receivers moving forward a while back.  I found the archived thread.  

http://www.ar15.com/archive/topic.html?b=3&f=4&t=506101

Great find from someone that has handled quite a few more than I have.  It's nice when you get repeated data with identical results.

You were able to use this on a Mega upper? I was told the tolerances were to tight.

I haven't handled any Megas personally, but the last one I did was the BCM for my 300BO pistol build.  It was quite tight as well, so I put lube on the tool with a little bit of the compound onto the shaft of it and slowly worked it into the upper.  Had my son hold the drill with the tool in it and spinning and steadily lapped the tool into the upper. Took a bit of extra effort but worked just fine.  I'm guessing this would work for most with tight tolerances.

Radian23, is this what you did with the lapping tool? Wouldn't that cause tolerance issues with the BCG.

First, let me say that I agree with you whole heartedly.  It's not unreasonable to insist on evidence for any claim made by anyone.  Aside from the large issues you mentioned of timing and barrels being off center, lapping uppers is really splitting hairs when it comes to accuracy.  I have also yet to see one piece of evidence (a white paper or such) for lapping that could pass through the peer review process used by science, academics, or industry.  That is what I was talking about before; here is where I disagree with you.

It does need to be as involved as I stated above.



ONE rifle cannot be used as a benchmark.  In statistics we use population samples to characterize data sets.  What you are suggesting is equivalent to saying "Since this one man was measured to be 6 feet tall, all men must be 6 feet tall; unless how we measured him is wrong".  As you can see not only is this statement wrong, but the methodology of arriving at that statement is wrong.  Furthermore the method by which we disqualify our experiment is wrong, by saying the only way all men are not 6 feet tall is because we must have measured the first man wrong.  In this case the whole thing is incorrect.  You could only carry out this experiment by taking a population sample of rifles and extrapolating the large amount of info to the entire population of rifles.

Either way I think the point is moot because now we're just splitting hairs.  But that is what I get paid to do, so I thought if we are going to split hairs we might as well do it right.

The bolts head-space won't change. The BCG has a little little extra room inside the upper, fore and aft. Lapping should only remove a very small mount of material, mostly anodizing.

The only thing lapping will do is square the barrel a bit more to the upper receiver which will only really help keep your rear sight centered. Lapping will also allow you to time your barrel nut, essentially the same idea as using shims. Unless you have a really out of spec upper, lapping will do nothing for accuracy. Also be aware, that if you lap too much, your barrel extension could protrude past the feed ramps inside of the receiver. If this happens you'll have feeding issues but it would require a good bit of lapping.

I've tried lapping and other than the timing thing, it didn't do anything. It would also be very hard to prove if it works or not. IMO, it does not.

Didn't lapping start with the Grendel crowd 10-12 years ago?  It was done the ensure bolt lug to BE lug contact is squared up.  I know it cured some Grendels from breaking bolt lugs  I bought the lapping tool for my G and use it on all builds.

The test does NOT need to be involved just to find out if there is any change with ONE rifle.  After that, you do a deeper test.  This is called "science."  If you have a theory, you do a test to see if it holds up (one rifle), and if it does, you test further.

Old Tool and Die Maker here.
I had to lap the front of my Noveske receiver, so I could time their damn barrel nut.
Using their barrel also.
Yea it was a pain in the ass, but it worked.
Took a few times. With total cleaning of the upper receiver each time.
With great care to not take off much.
I haven't had that problem with Mil Spec barrel nuts before. Have had to torque more a couple, than 40 ft lbs. though.
But there isn't anything mil spec with Noveske's barrel nut. Think i wound up a bit over 60 ft lbs.
It looks just fine, and works the same.

Built up a 300 blk and when trying to sight it in at about 50 ft I could not get consistency. As the barrel would heat up the POI would move to the right. Let the barrel cool. POI was back to the starting position. Repeated this several times and had the same results with a Burris F3 and iron sights and 2 shooters.


The only thing I can think of is the receiver is not squared. Even a lousy barrel will not be that bad at that distance. Used hand loads and thought it could be the bullets I was using, but others have had decent accuracy with them.

I will get a tool and lap this upper and see if it makes a difference.

If you asked a machinist to do it right, they would make sure that face was square to the centerline of the action. You can do that by machining a mandrel and and mounting the upper onto it and using a cutter on the lathe on the face of the upper. You can also do it with a lapping tool.

It has nothing to do with how much of an improvement it's going to make. It has to do with making the job right.

B

Don't know how much it helps accuracy, but I tried it for the first time on my new build. before lapping the hole in the barrel nut didn't line up with the hole in the upper at 35 lbs. Still didn't line up at 60 lbs (max torque recommended by MI). After honing (it did start removing on one side, so apparently my upper wasn't 'perfectly' square') the holes lined up perfectly at about 45-50 lbs - more than the minimum and less than the recommended max. So yes, it CAN help if you don't like over stressing the barrel threads on your upper and/or your barrel nut. As always, YMMV...

I agree but don't waste your time arguing with the masses here. You are out numbered.

I bought the tool because I got a discount equal to the cost from a vendor.

There was no back to back shooting to ascertain any benefit. When you study into barrel ballistics, buying an air gauged barrel with guarantee it will shoot .5MOA would be money better spent, and then getting into reloading would deliver even more accuracy.

Lapping? For many precision makers, it's still an extra charge, not standard procedure. There is where it ranks in their scheme.

If you are trying to index the barrel nut, it could be a help. So could nut shims, you could try them, too. Some free float makers suggest that, first.

The tool can and does true up the nose of the upper, and it does smoothly grind down the length of the threaded area. Got too far indexing a nut and you start over. We really aren't talking much as it's just one toothed notch at a time, not turns. It's 1 1/4 by 18 threads per inch.

In terms of accuracy, there are still other factors - like how the barrel extension is threaded to the barrel, and how square the shoulder is on it, which is the other half of the mounting. You aren't mounting the barrel directly, you are mounting the barrel extension.

Therefore you still need to lap the mounted barrel extension to the bore centerline - good luck with that.

The nose of the upper is just one part of a much more complex arrangement, and again, precision builders are charging extra to bother. Their warranty stands without it, which should tell you that good parts alone do most of the work. it's the cheap out of spec parts than need truing up.

Again, I bought the tool, in just a few turns I leveled out the anodiizing color, which amounts to a few .001's. How many turns of elevation or windage does that amount to? One a poor quality upper, it might center things back up. Add the cost of the tool to your shopping price to the front door and you will likely never experience the problem.

I'm building an AR pistol and I might  lap the upper to check out of curiosity more than any attempt to make a 150m max gun do better. For all the factors involvled, it's really more because I now have it rather than spend money on shims.

Thanks for reminding me it's sitting in the gun tool box. I forgot.

Good thread. Thanks for the intelligent dialogue. I have learned a lot just reading along. I don't have a lapping tool but see where it could be useful.
Thanks for a good thread.

Sorry for the completely late reply.  Been working too much...  Didn't have any issues with the Mega receiver and using the lapping tool.