I placed, yet another, Midway order the other day and threw in an upper lapping tool. Its only $23 and after seeing how uneven most cast uppers are machined I figured it would be a good idea to start using it on new assemblies. Cant hurt. Along with the fact Im going to start bedding AR barrels on everything I put together. We did a barrel of my friends AR last weekend. Not sure if it helped but it sure didnt hurt.