This isn't a handgun ammunition question but more one in general but I couldn't find any general ammunition area to ask.
Basically I know a gun will shoot differently with different kinds of ammo so if your gun doesn't shoot good groups with one you should try another. What I'm wondering is if you take four new Gen 4 Glock 21's for example, not sequential just four pulled at random and shot them with the same ammo would they shoot the same? As in have the same pattern size and such?
Same with AR's of the same kind or hunting rifles. If you had 5 new rifles of the exact same model and caliber and one shot great with "type X" ammo would the other 4 shoot just as well with the same ammo? Or is it that every individual gun, even if they are the same as the next gun with the only exception being serial number, will shoot differently?
I was thinking that if the same model/caliber guns shot the same you could build a database of guns and what ammo they shoot best. That way when someone buys a new gun they could look it up and try the top three or so instead of having to try several brands of ammo to see which works best. It wouldn't help with used guns I don't think because the barrel wear being an unknown.