While the manufacturing process is shrouded in understandable proprietary secrecy, the following is generally acknowledged.
X-Act is the same ammo as Midas + and Center X. It is different only in that the grading process determines what lots become X-Act. Other lots become Midas, still others CX.
A single production run may produce lots of each variety of Lapua standard rifle ammo (X-Act, M+, and CX). Expect a production run to produce fewer lots of X-Act than Midas, and fewer lots of M+ to be made than of CX.
Just as they grade the ammo, the match ammo makers grade each ammo component -- e.g. the bullets, the casings, the propellant, and the priming compound. Perhaps even lubricant can be graded, or at least freshened as appropriate.
Lots are distinguished from each other by a number of factors, including the grade of the components, by adjustments to loading machinery, by the replacement of parts, by the change of technical personnel etc.
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What follows is speculation. It may be reasonable to expect that ammo makers such as Lapua intend the component grading process and results to help make their ammo as consistent as possible. In other words, it's possible that Lapua seeks to use the best grades of components in the best grade of ammo, so that X-Act is made of the top graded bullets, casings, propellant, and priming compound.
If the above is correct (remember this is speculation only), this would presumably involve the loading machinery to be "loaded" with the constituent components in such a way that they come together in the actual loading process at the same time and place. In short, the best or top-graded components would be arranged to become X-Act.
The components graded to other "levels" might be arranged to come together in the loading process to produce the next "grades" of ammo, Midas + and then Center X.
If the loading machines and loading process are themselves characterized by the production of better products at certain points in the production run -- e.g. at the beginning or in the middle or toward the end of the production run -- then this can be taken into account when preparing the run.
If it can be taken for the moment that the above is close to the way the ammo makers approach the production of ammo, it would mean that the ammo could be graded by what it is supposed to be. In other words, the best components are supposed to become X-Act, the next best Midas +, and the next best after that Center X (the left over becomes pistol ammo?).
In short, a production run might be tentatively graded according to the components and possibly by where in the production run they come together.
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Some additional speculation:
If true, this would potentially make unnecessary the tedious process of testing by shooting, something that would surely be a time-consuming bottleneck to ammo production. Testing by shooting could serve to additionally confirm the grading process.
If true, this might explain some things. While the process described may work well most of the time, there may be batches of ammo that for one reason or another aren't what they are supposed to be, that is X-Act or Midas, or Center X. This might account for why some X-Act is outperformed by some Midas, and why some Midas is outperformed by some Center X.
In other words, if true it might explain why sometimes shooters get a lousy lot of X-Act or other variety of match ammo. Sometimes a system that works most of the time doesn't work all the time.
The above is of course speculation, guesswork that may or may not be close to the mark.
