Aero AR10 upper receiver lapping question

[bikemutt]

I started work on a new AR10 build and decided to try my hand at lapping the upper receiver to ensure a real square and clean barrel fit. I'm using the Wheeler Engineering kit. I did feel a tiny bit of slop with the tool in the receiver, used one layer of Scotch tape at each end which has taken out all the slop.

I could definitely see and feel the top of the receiver was lower in height than the bottom. I followed the instructions (no comments from the peanut gallery of disbelievers, lol) and quit once I could see shiny aluminum all around. Upon magnified inspection I see more roughness right around where the slot is, around 10 to 11 o'clock if the slot were are 12 o'clock.

I think I could/should go in just a bit more to see if I can smooth that out, but I don't want to go too far if I'm overthinking this. Hoping someone here who's done this might help me with some guidance.

Thanks!

 

[BBBBill]

If it is only that one tiny little divot, then I would stop where you are. Put some layout fluid on the face of the receiver, insert the thoroughly cleaned lapping tool, give it a turn, and see what it looks like.
FYI, Joe Carlos, one of the top AR builders, has said that he had terrible results with that style lapping tool and will stick with lathe truing in the future. He has written an outstanding series of articles on AR accurizing for American Gunsmith. Amazing what things do/do not affect accuracy on that platform.