Here is a good method for testing crossbow bolts for precision.
Sight in and set a target on 50 Meters. Install a spirit level under your scope or at the part that holds the bows to make sure you hold the crossbow always straight! The scope mount of a crossbow sits much higher as on rifles so every turn to left or right puts your arrow out of center.
If possible make that test without much wind.
Mark 6 arrows at the vanes with numbers from 1 to 6.
Use the attached sheet that I made to write in where the bolt hit the target (you can mark different shots with one arrow at the same target). Now you can see when a bolt doesn´t hits the right spot and you can sort them out. Some times it is simply your own fault but if the arrow hits always an other spot than the bulls eye you know that something is wrong with that bolt!
I´ve tested all my match bolts with an rotating arrow tester and all looked very very good. Than when I shot them and there was a few which had a deflection up to 10 inches and hit not where i aimed, even when this bolts goes every time to the same spot outside the v-bull. Could happen because the vanes or something else but they are real not to use.
This test is easy and make a lot of fun, specially when you know later you have real perfect material to "work" with
An other important tip (also for rifles). Many people pull the trigger from inside the bent finger and this is wrong, specially if you have a more heavy trigger like on crossbows. Always just use only the tip of the finger

Otherwise on hard triggers you pull to much to one side.
Forgotten: one vanes should have an other color so put the number there and than put always this other colored vane into the crossbow rail ! The vanes can have an effect on the flight and if you put it different ways into the rail you don´t get a correct result!!