I hate to over simplify things after all the effort you put into this. Not everyone is a gun person. 300 rounds equals 6 boxes of 50 rounds. There were some that said 500 rounds or 10 boxes of ammo. The amount of range time to fire that much ammo gave the gun owner enough time to become familiar with the gun. The operation and take down, cleaning etc. Usually it takes several trips for the average shooter to burn that much ammo. Hopefully they learn to hit with it. The action should smooth out some and any problems be resolved. It wasn't a magic number just to prove the gun works. It is a combination of break in time for both gun and shooter. I like to run 100 rounds through a new gun more to learn the gun and how it shoots than reliability. You can have two of the same model and caliber and the poa/poi be different. Shooting helps with any gun. For a couple years almost everyday I fired at least one shot at a steel target with my carry gun. When I stopped I had hit every day for almost a year. Target was full man at 100 plus yards. It is not a magic number, it is shooting enough to build confidence.