As the barrel travels through the manufacturing process there are key points where measurements and materials need to be inspected.
These include steel make-up, bore diameter, groove diameter, hole straightness, surface finish and profile concentricity to the bore. Each one of these points of inspection require a unique and calibrated measuring instrument. As a start, each batch of steel comes with its own certificate stating the exact material make up and hardness upon delivery. It will also describe any heat treatment and stress reliving processes its been through so we can make sure there will be no movement in the initial gun drilling stage.
To measure the bores/lands of any given barrel, we use hardened, UKAS calibrated bore pins with increments of 0.01mm. For the rifling groove, we use a custom ground Dia-test split ball probe on a 4" extension which is custom ground to fit in the small rifling grooves. These are attached to dial test indicators with an accuracy of 0.0001 of an inch. We feel this is one of the most important measurements to take as it determines whether you have a gas tight seal round the bullet/projectile.
Any groove diameter wider than the projectile will allow some gas to pass it on firing and creates an inconsistent and unstable atmosphere for the bullet to travel through.
Finally, all barrels have a visual inspection along each land and groove using a HawkEye DV-Borescope connected to a 25" HD tv. This picks up even the slightest of marks and blemishes at 20x magnification; it also gives a visual picture of the rifling form and helps us identify any ratcheting that may be taking place. These are just a few descriptions of the inspection process's we use at Sassen. In the rare occasion that a barrel blank fails any part of inspection, it is immediately scrapped and re started from the very beginning. This robust policy ensures we will never deliver a sub standard barrel that won't get the firearms maximum potential accuracy.