Due to the inherent nature of NP3 Coating, tooling marks may be present on SIONICS NP3 Coated Bolt Carrier Groups. Tooling marks are COSMETIC and have ZERO effect on function. Being that the NP3 Coating impregnates into the host material, it is much thinner and much less forgiving in hiding Tooling Marks. Other popular coatings such as Phosphate and Nitride are thicker and darker in appearance, allowing for tooling marks to be easily concealed. Regardless of tooling marks present on SIONICS NP3 Bolt Carrier Groups, every SIONICS Bolt Carrier Group is backed by our Lifetime Warranty that covers any manufacturer defect that would affect function.