A very scientific principle is applied. They place the muzzle between two steel pins on a table like fixture and another pin is inserted just forward of the handguard and the gunner simply bends the barrel in the direction it needs to go in order to change the point of impact.
In the business it is referred to as IF IT WON'T SHOOT STRAIGHT BEND IT, IF IT WON'T SHOOT BENT STRAIGHTEN IT.
That is not on the drawings. You have probably seen pictures of lines of tooling suspended from ceilings in gun factories with folks looking down barrels and turning wheels on the bottom that apply force to middle of barrel. Many barrels are crooked internally so apply force to straighten the bore internally.
Simplified is it what you do when you wash your car, you bend the hose to direct the water where you want it to squirt.
The acceptance dispersion was relaxed in order to get more ammo accepted and since we were on 386 the adjustments were made on the SCAMP line to allow more tolerances. The looser the tolerances the more ammo gets fielded and less they have to sell to us. The adjustments reset the laser gauging so less is rejected.
All this ammo you see sold in bulk is reject ammo that is allowed so the contractor can recoup costs.
IIRC the acceptance ammo spec was 1.5" MR and the ball was 2.2" when I shot the M16A1E1 test. When we had multiple arsenals that manufactured on manual lines occasionally lots would be produced that shot exceptionally well and the 5.56 that printed 1.5" or less was earmarked for weapons acceptance testing. Now we only have Lake City and the SCAMP lines and they can produce 77 million rounds per day last I talked to the Chief of Ammo engineering right after he retired down in Florida. Last I heard he was making trips all over as a consultant.
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