So my long time friend is a machinist/metallurgy and was telling me that lapping an ar15 upper removes the hard coat anodized coating and exposes the soft aluminum which totally reverses the purpose of hca. He said if your going to be lapping it I should do so very sparingly so not to remove all the hca. He measured 2 of my aero uppers and they were almost perfect so I didn't do the lapping but did bed the barrels with locktite 640 and they both shoot lights out. What are your thoughts on this. If we buy quality parts is it necessary to be lapping or not.
Quality parts? probably not, I do agree with your friend at least in part. The purpose of lapping is to remove any high-spots or imperfections on the circular mating edge of the upper, not to grind down the entire surface some amount of mils. With any mechanical process there is always a possibility of one or more imperfections left on the surface. Removing that high spot should not endanger any anodizing. Further, the lapping only is to improve on that one, narrow circular edge ("top" of the upper against which the barrel flange rests) therefore all anodizing on all other surfaces will not be touched.
I don't know how deep the anodizing treatment goes down into the metal, but IMO a bit of lapping should not remove all of it.
You get a couple of things when you get a good quality upper rcvr: concentricity, bore-alignment, tight-fitting to the barrel extension, excellent mil-spec dimensional adherence, etc.
Lapping will not make a poor upper a good one, it can make a good one really good... properly done.
If yours didn't need it you're gtg. Some of mine did and some didn't. I'm happy with all of mine.
"Down the floor, out the door, Go Brandon Go!!!!!"
I want the most square lockup I can get for my bolts lugs. So for me I don't care if the upper cost me 20 bucks are 200 bucks I'm going to lapp the reciver face and then do a compression fit with ss shim stock and by freezing the barrel and heating the upper so when they return to normal room temp they are a very tight compression fit.
I never bedded a barrel w/loctite and see no reason to.I tighten the barrel nut 40-60lbs.I never had any movement between the barrel and the upper receiver .I have several friends who bed their barrels with Loctite red.And none of them have real proof that it has improved accuracy. They just to do it,because they were told to.
But,I do use a lapping tool to square the face of my upper receiver.I have proof that that does improve accuracy. All of my AR builds are shooters!
A5BLASTER & FLshooter, do you lap until the whole surface is exposed raw aluminum or just enough to get rid of any imperfections from the hca. I did 2 of my others but only slightly lapped so most of the hca was still intact.
sbowhuntr Wrote:A5BLASTER & FLshooter, do you lap until the whole surface is exposed raw aluminum or just enough to get rid of any imperfections from the hca. I did 2 of my others but only slightly lapped so most of the hca was still intact.
I lapp it till it's uniform. Most times that means it is bare aluminum. Sometimes not.
Lapping in my mind doesn't really do anything for accuracy. But it does tones for bolt life. Squaring it up makes for a much more square bolt lock up and longer bolt life.
Several years ago I purchased an unknown maker complete upper off an auction site. I had to move the rear sight almost completely to the left to get this thing to hit the target. There were other problems with it as well. Long story short, I pulled the barrel and lapped the upper using the wheeler tool. The right side of the face was very high.
I won't be able to tell how much of a difference it made as I had to replace the barrel anyway. But with a new barrel and lapped upper, we'll see where the sights line up when I can get it to the range.
Some say lapping does no good. I say it can't hurt. I do it to all of mine that I build and they are all very accurate shooters.
sbowhuntr Wrote:A5BLASTER & FLshooter, do you lap until the whole surface is exposed raw aluminum or just enough to get rid of any imperfections from the hca. I did 2 of my others but only slightly lapped so most of the hca was still intact.
Whatever it takes. I’ve done every one of my other receivers and it’s been very minimal. Haven’t really had one that that was very far off. I wouldn’t worry about exposing some of the raw aluminum. It’s going to be covered by the barrel and torqued to at least 40 pounds,nothings going to hurt it.
A5BLASTER Wrote:I lapp it till it's uniform. Most times that means it is bare aluminum. Sometimes not.
Lapping in my mind doesn't really do anything for accuracy. But it does tones for bolt life. Squaring it up makes for a much more square bolt lock up and longer bolt life.
A5BLASTER, great explanation of why to lap regarding bolt lock up and extended bolt life. Never had it explained to me that way, thanks!
You might want to keep an eye on the cutting surface of your lapping tool after you've done a few because the steel it's made from wears too.
Mine has been chucked in a lathe and redressed a couple of times.
I face every receiver I do on the lathe with it mounted on a mandrel between centers. Many years ago I was talking to an equipment specialist from R.I.A. about the then new M110 sniper rifle. He mentioned that Knight Armament ended up having to bed the barrel extension in order to achieve accuracy requirements for the military. I did remove a forend from one later just to check it out and they were DEFINITELY bedded with an epoxy type compound.
So I do face and bed my bbls in the uppers I assemble/build. I also use quality cut rifles blanks and chamber as I would a benchrest bbl through the headstock. On an AR15 platform I expect better than 3/4 MOA and it most often is better than 1/2 MOA. Over the years I know I’ve done well over 200 AR barrels from an unturned blank. Those are just my experiences.
02-02-2020, 04:24 PM (This post was last modified: 02-02-2020, 04:27 PM by Old Bob.)
I've lapped two uppers. One barely needed any lapping at all. It still has some anodizing left but it is visibly thin. The other needed more lapping to even up the receiver face. It now has a distinctive half-moon look to it. A third receiver (Precision Firearms) was so tight my lapping tool wouldn't fit in the carrier channel so that one went un-lapped. I clamped the receiver vertically in a vice with a bubble level centered on the face. I rotated the level 90 degrees & the bubble was still centered. It obviously didn't need lapping anyway. I had to warm it a bit to get the barrel started. This same barrel rattled around in the receiver (BCA) it was in before.
I refuse to be victimized by notions of virtuous behavior.
I just got done lapping one of my receivers. Bought the wheeler kit with the polish. Went really slow, making sure not to overdo it. Will have to wait to see the results. I?ve had good luck with this barrel so far. If I get good results I?ll lap my other receivers. Fairly simple process, certainly improved the barrel fitment. Not as much wiggle.
