These are two types of testing we do on all of our Bolt Carrier Groups.
HPT or High Pressure Testing, is another test performed by firing a high-pressure cartridge through the BCG being tested. HPT is done first to expose any potential flaws in the bolt. Then MPI testing is done to find any flaws or potential flaws.
MPI or Magnetic Particle Inspected, is a testing method used to test for microscopic cracks or fissures created during the manufacturing process. To test for this, the BCG is placed inside a magnetic field and a liquid solution containing magnetic particles is then applied to the steel. The magnetic particles will stick to any cracks, fissures, or tiny imperfections that are on or just under the surface. If any cracks, fissures or imperfections are found that BCG is scrapped.