Jiro said "Likely" which can be true. Not always the case, I did compare different ammo and yes there are differences in it.
For example, when I bought shotgun shells from wally world, they are POS! as compared to high quality sporting center offering higher quality of shotgun shell. Mind you, both are same brand, everything is same except the base, Wally world use tin for the base, while high quality sporting center shell got brass for the base. A HUGE difference in accuracy of shooting.
Also, if one doing re-loading, depending on quality of materials used.
As for police, they need higher quality ammo, for few reason, one is safety. Poor ammo can explode before it even projectile the lead, injury the shooter (Rare but happens), secondly I noticed POS don't shoot well with accuracy like high quality does. So, police need that to reduce oops with shooting like this unfortunately incident.