MP and HPI barrel testing

[Clark_Kent_X]

when a barrel says MP tested what does that mean? and when it says MP and HPI tesded. what is the differance with just the MP testing alone?

[MT1]

MP is Magnetic Particle inspection, HPI is pressure testing I believe(High Pressure Inspection?). The MP test involves mounting the barrel in a wet mag machine, creating a magnetic field in the first plane then second plane and washing it down with iron particles suspended in solvent, a black light shows any cracks that are visible when the iron particles are drawn into them. We do this with crankshafts, connecting rods, etc. Dry magnafluxing is done with a powder on heads and blocks.

Pressure testing is simply pressurizing the barrel with air and inspecting for air bubbles when either submersed in water or when sprayed down with a bubble solution.