After watching the "How To" video in the product description and reading the reviews, I figured there are folks who buy the product and don't do what I did and are surprised that they aren't able to use the tool or get it to fit. The mandrel portion that fits in the upper receiver fit mine like a glove, just perfectly, so even if the lapping face is not perfectly perpendicular to the receiver mandrel, the tool will still create a flat perpendicular surface on the receiver face.

I had concerns that the Aluminum Oxide lapping abrasives carried by Brownells was too fine (600 and 800 grits) to get the job done, but the receiver metal is 7075 T6 aluminum, very soft vs. steel alloys, and worked like a champ.

In one hour I had my 4 stripped uppers lapped flat. Not one of them was flat to begin with. Next step is to dismantle my ARs already built up to square those upper receivers and see how much improvement in accuracy I can get!

I purchased this to see if it would improve accuracy in my AR (6.5 Grendel). I used this on an Aero Precision upper, and surprisingly enough, it was pretty square. It did however square the receiver (as seen by the removal of material). I can't say that my rifle went from field grade to super match, but a little accuracy could be seen. My biggest complaint is the area where the drill is chucked. After use on 2 receivers, it slipped 4 times, requiring it to be re-chucked. When I finished, I noticed that the metal had actually deformed on the tool (where the drill chucks) and marred it pretty good. I think if it was shaped into a triangular shape, the grip would be better and it would last a bit longer.

Tool is either out of round or is too large for every upper I've tried to insert it into. Complete waste of time and money. I expected better from Brownells.

This is a very good idea and a very useful tool...if it is machined to proper specs. The easiest way to lap the receivers is the chuck this tool up to a lathe and then run the upper over it. However, if you try this you will quickly find that the tool is horribly out of true. If you are lapping with a drill you may or may not notice this but you will likely not get good results. Fortunately there is enough excess material on the outer diameter to allow me to turn it down some and get it round. Once trued the tool works great. Another thing to mention is that (if you have the capability) the tool will continue to produce the best results on future uppers if you reface the lapping surface after every receiver. The anodizing on the upper tends to wear down the steel a little.



The best approach I've found for lapping is to coat the shaft that goes into the receiver with a generous coating of moly grease. This keeps the chamber from acquiring wear during lapping. Afterwards the grease can be cleaned with brake cleaner. Then wash the receiver in warm, soapy water and it will look good as new. For lapping, apply a coat of compound to the tool and while spinning the tool (I was running at 100rpm) apply heavy and equal pressure to the receiver. You will hear some light grinding for the first five seconds or so. That is the lapping compound doing it's thing. After the grinding sound goes away, hold the pressure for another five seconds or so and then release, wipe the used lapping compound off the tool and reapply a fresh coat. Repeat this until the face of the upper is uniformly silver. The reason for the short intervals between reapplying the lapping compound is that the anodizing on the upper is very hard and breaks down the compound rather quickly. If you continue to run the tool for too long you will either start to wear down the tool, achieve minimal work or both.

Simple, but nicely made tool. Nice snug fit in receiver, so I knew alignment was good. Took very little effort with 180 grit aluminum oxide lapping compound to see results. This may, or may not, make my rifle more accurate, but it definitely trues up face of receiver so barrel extension has a perfect surface to mate to. Can't be a bad thing! Another variable I don't have to worry about. Thanks Brownells!

This tool works great. View the video that Brownells has on the site and read the directions and you'll be fine. Go slow and check your work often. Don't run for the 10-15 seconds between checking as the instructions say. I'd check every 8 to 10 seconds. This tool works quickly.

I removed and lapped all of my other AR rifle builds after the great results I experienced from lapping my 6.5 Grendel build. I was surprised how much this improved my 5.56 and 6.5 Grendel rifles accuracy. None of my uppers were square until I used this lapping tool. It worked just as it was suppose to and I can recommend this tool with out hesitation. I now use it on all of my AR builds.

Bought this a while back in anticipation of assembling a match AR. When I received it there was a burr, as if it had been dropped or hit hard, on the leading edge. I cleaned the burr off and - it wouldn't fit into either AR receiver. I tried moly grease, red grease - nope. I put it up and it sat in my tool box for over a year. I was set to build 5 hunting uppers in various calibers and tried it again - would NOT slip into any of the receivers though all barrels were nice and tight slip fits in all receivers. Took it to a local machine shop that said they'd take it down to a slip fit in the receivers I brought in but the set up and work charges were quite a bit more than I paid for the tool. NOT up to Brownells usual high standards.

I picked up a virtually new complete 300 Blackout upper for a ridiculously low price from a frustrated gent at the last gun show. It was built with very well known quality parts--but even with the windage cranked all the way to the left, it was still hitting 3" from POA at 25 yds. The barrel looked straight, so I figured I'd take a chance--Glad I did because it turned into my gunshow deal of the year!

I don't have a lathe, but figured that Brownells would have something---this tool worked exactly as advertised. I used Permatex 100 grit valve grinding compound and went slow. It took less than 5 minutes to true the receiver. *You do need to make sure that the tool fits well--I can see how you could run into problem with an out-of-spec upper.

My new upper is now zeroed perfectly at 100 yds and I'm only 2 clicks off the rear sight's mechanical center. Very happy customer!

I have used this tool on all of the L.E. and match guns I have built. I find it extremely easy to use and an important tool for the accuracy of any AR rifle built

Product works as described. Bought this tool for a 6.8 SPC accuracy build I am currently working on and tested it on on my 5.56 carbine's upper receiver.

I used Brownell's 600 grit aluminum oxide lapping compound along with this. Brownell's suggests 180 grit, but the 600 worked just as well, just a little more time involved.

Before test use on my carbine, my red dot would not co-witness with the front sight since the receiver was (apparently) not square. After using this tool the barrel lines up perfectly for absolute co-witness with the sight, and I don't have to max out windage on the red dot!

The inside of the receiver has no signs of marring or scuffs from the tool, which I kept well lubed on the inside of the receiver with moly grease.

Highly suggest this product, and will use on all future builds.

Easily damaged using drill chuck, will wobble and destroy an upper receiver. Also easy for lapping compound to migrate into receiver and strip teflon coating. Very tight fit, couldn't find an oil that worked well but didn't try a mil-spec grease which might work better given the pressure. Don't use this tool if you can't spare the upper and try again on another.