Lapping the upper receiver face?

[traybill]

I have started collecting parts and tools to build my first Ar-15 I have been reading alot of tutorials. There has been mention of lapping the face of the upper receiver for square contact between the barrel and reciever. Brownells caries a lapping tool for this purpose. My question is how necessary is it? I want to get all the accuracy out of it I can.

[LRRPF52]

I would say that is only necessary in an out of spec upper, and there are trade-offs if you lose the anodized surface of the upper receiver extension. I'm not sure how much this is a factor in the AR15 really, but I have seen a gunsmith who has done it regularly printing sub-1/2 MOA groups at the range with a Grendel. I've also seen billet upper Grendels that shoot in the .2's, with Satern barrels. The biggest factor in your accuracy is the quality of the barrel, so you should seek out the best you can buy. It probably wouldn't hurt to go with a beefier billet upper as well. If the billet upper is made by a company adhering to ISO standards with laser check stations, there should be no deviation in the face of the upper from square.

I also like uppers for precision rifles where the barrel extension fits very tightly into the barrel extension channel, although it just feels right and I suppose it helps fight barrel whip more.

[traybill]

Thanks for the reply. The loss of the andonized surface had occurred to me. It seems that the lapping might be a carry over from truing steel receivers in bold action rifles. I dont know that the alluminum receiver would be hard enough for a slight imperfection to keep the barrel form tightening up true.

[traybill]

should read bolt action not"bold" fat fingers

[LRRPF52]

The same gunsmith said he also trued the threads on the barrel extension, trued the bolt face, trued the lugs, trued the barrel extension flange, and trued the barrel nut internal flange IIRC. He also did a meltdown on the feed ramps and receiver blending to the barrel extension. His rifles looked beautiful when it came to the internals. I saw him only once at Lee Kay Shooting Center in the Salt Lake Valley, and lost his contact info.

[traybill]

Its looking like this build might turn into a build it and tinker. To see if I can get more out of it. I think I'll put it together and see what it produces for groups and if I'm not satisfied with it then look at lapping the receiver.

I agree with what you said earlier about accuracy coming from a good barrel first off. In my experience with other rifles its the barrel, trigger, and sights (scope) in that order. So with those I'll get the best I can afford.

[jkingrph]

I would not think removing the anodizing on that surface would make a difference as nothing is moving there, the barrel extension shoulder is simply pressed against it very firmly. By lapping you are just making that surface more uniformly flatter and smother for better contact.

I did a couple using the tool from Brownells and did notice some high and low spots in the mating surface on my uppers, different brands, so they may be some merit to the process but do not really know.

As far as removing anodizing, what's the big deal when M-4 ramps are formed the anodizing is usually lost and the bolt carrier eventually wears through the anodizing in a few small spots, at least on all the rifles I have, the ones I built, plus a couple of Colt H Bar sporters.

I used to fly model airplanes and in those little engines we had a steel cylinder lined and usually an aluminum piston, no rings just a tightly fitted piston. Some of those really small engines would turn up 20-25000 RPM. On larger engines the mantra for better moving parts was aluminum-chrome-brass, for maxium smoothness & better wear properties.

[traybill]

The only way to really see if it has any benifit is to put it together without lapping the receiver. Shoot it for accuracy then break it down and lapp it assemble it and shoot for accuracy again.

Maybe somebody has already done this type of test?

[elkbow]

i square all my upper receivers, and I have not found one that was square from the factory yet, i have both the cutter and lapper, i cut first and then lap....whether or not it helps with accuracy, don't know, but every little bit helps and its an easy chore if you have the tools to do it

[smoke13]

elkbow, I would be curious to see a picture of how you are fixturing your receiver for your lapping operation. Are you doing this in a lathe or mill?

[stokesrj]

Lapping is totally unnecessary, but if it makes you feel good, go for it. Removing Anodizing is not an issue either. If you were to send your lower to Les Baer to have them fit one of their uppers to it, they will mill the anodizing off the lower edges of the upper for better fit. I have one done that way and there has been no degradation of the surface at all in 5+ years.

I went to the NRA School of Gunsmithing to learn to build National Match AR15's, taught by John Holliger who owns White Oak Armament and White Oak Precision. John builds more AR's used to set national records than anyone. Frank White of Compass Lake Engineering would be #2 followed by RRA, Armalite, Bushmaster and so on. John is also one of the nations top High Power National Match Competitors currently ranked #27 http://clubs.odcmp.com/cgi-bin/natio...?type=EICRIFLE . When I asked him about truing receivers and lapping receivers he just kind of shrugged and said do it if you wan't but it's a sign of someone who hasn't figured out what is really important yet. Frank White doesn't true or lap receivers either. Between them they probably have 700-800 rifles on the line at the national matches out of 1400 competitors. Konrad Powers who won the Presidents match this year was shooting one of John's rifles. Also the AMU does not lap or true receivers. And they truly dominate the national matches.

John also told me that if he had to build ten rifles that would shoot less than .5 MOA he would choose the AR as the platform over the Remington model 700. He went on to explain that it would be absolutely necessary on the R700 platform to blueprint the actions and there would still be one of the ten that would not make the .5 MOA requirement and would have to be rebuilt. With the AR it isn't necessary, just use any good upper receiver, there are only three manufacturers any way regardless of how they are marked, and a quality lapped barrel and you are there.
That is why I say, start with a good barrel, and you are most of the way there, add a good trigger and you are in very good territory. The rest is mostly fluff assuming you have a free-float hand guard and used reasonable assembly techniques.
Anyway, that's the way I see it, I hope I didn't offend anyone, just trying to share what I have learned.
Bob

[Variable]

I believe your post to be gospel on this topic! I couldn't possibly agree more.

[elkbow]

elkbow, I would be curious to see a picture of how you are fixturing your receiver for your lapping operation. Are you doing this in a lathe or mill?

No, hands tools, from brownells:

http://www.brownells.com/.aspx/pid=20449/Product/RECEIVER-FACING-CUTTER-PILOTS

then lap by hand:

http://www.brownells.com/.aspx/pid=20220/Product/AR-15-M16-UPPER-RECEIVER-LAPPING-TOOL

I do mount in a vice, I have a rod that is the same size as the pilot that I slide in from that back that flushes against the tool pilots

I do agree with comments above though, it is probably fairly insignificant in the big picture of things

[traybill]

I've collected all my parts will be puting it together soon at this time I wont be lapping or trueing the receiver if I dont like the accuracy I get I'll break it down and lapp the receiver. I have a friend that is planning its twin he's going to true the receiver we'll compare and see what we come up with.

[elkbow]

you'll be fine without lapping, hard to tell if it helps much if at all, as said above other things are more important like a good barrel....and a good trigger lol