Not built right - avoid - Wheeler Fine Gunsmith Equipment Delta Series Variant Receiver Lapping Tool AR LR/10

The concept of the lapping tool sounds good. I do see how the mating face of my AR10 upper could affect accuracy which lapping would "True" the alignment to the BCG and barrel extension, which seems like it couldnt hurt to squeeze out a little more accuracy. However this Lapping tool is poorly built and executed. The lapping face of the tool is too narrow and doesnt go to the outer edge of the upper mating face. It is also poorly machined and has a "grooved" face which put round/circular depressions in the mating face of my upper. If I hadnt caught it soon enought it could have ruined my upper all together. I would avoid or buy a better quality lapping tool from an other manufacturer.