The short answer is nothing.
The longer answer is are you a reloader and lots of years of trigger pulling.
What I can say, its that at best a human being is capable of holding 1/4 inch if the equipment is capable of shooting it.
Back in the day when I was riding cycles, someone like Kenney Rogers would be able to beat me on a Honda VF750 vs my Nighthawk S.
If I had the VF 750 and he had the S, he would still beat me.
When you look at MOA claims, its with a very specific ammunition.
I once bought an AR that claim to be sub MOA. It was not, but when I asked for anew barrel it was, you specified the short barrel (which we offer) but that MOA does not apply to modified guns. Really?
If you got a Savage and it had a good barrel, you might get 1/2 (assuming you can shoot that).
You want to go tighter still, then you need to be David Tubbs.
The Savage is a good place to start, get a caliber that is not a barrel burner (308 holds up well) re-load, shoot about 5,000 rounds at which point if you can shoot you will see the barrel start to go.
Get the single shot with the Red Trigger that you can adjust to 8 ounces.
Then if you really want to see how good you are, get an aftermarket barrel. Litja, or the like in cut rifle. You better anticipate, you are going to waist 6 months or so.
Savage with the nut system you can replace the barrel and head space it yourself. A gun smith can do it for low cost due to little work involved.
Want something in between, get a Shilen Match or a Criterion. Good barrel and if you can shoot that will take you into 1/4 area.
After that, unless you just want to do a one hold once in a while, its custom rifle that cost big bucks.
Shooting is a system. Its the shooter, its the ammo, its the gun. Any one of those that is sub par, you won't do what you want.