[NewRomeTacitus]

Mmm, perhaps my skill with firearms could be a factor? (no ego intended)

I consistently outshot everyone in the units I was assigned after basic training, where I had to literally hold the loose Vietnam-era passdown rifle forcefully against my shoulder well in order to qualify. My DI couldn't even hit the damn target when I passed it to him, but he wouldn't get me a better one. Hence I used a piece of crap to get Marksman where most would have washed out.

Upon realizing I had a real talent for it I found I was automatically disqualified because of needing corrective lenses (1984). It's not easy to learn that any soldier today who requests it can get radial keretonomy surgery at no cost and can therefore qualify in the field I so hoped to join (and yes, I was custom made for the tedium, discipline and hyper-awareness of the craft). Life be cruel but I cheer for our snipers whenever their great work is recognized. Their load is the hardest yet their work yields the highest results for the least material investment.

[Shooter 2.5]

In order to find out what the rifles themselves can do, you have to eliminate yourself as the factor. In other words, you have to literally put the rifle in a vise with a good machine rest and like I said, put one heck of a magnified scope on it. Anything over twenty five power is probably overkill.
Using the suggested velocity and bullet weight can shrink the groups a little bit but not as much as the rest and scope.