Re: new gun or not
It sounds like you're already shooting pretty well with what you have.
So if you buy a new rifle, you may want to do so in order to gain some functionality that you don't currently have as compared to expecting some big accuracy gain.
e.g. different caliber, bolt, semi-auto, tactical, carbine, etc...
Alternatively, you may want to start handloading. Factory ammo seems to be working for you thus far. But, it will let you down as you continue to use it for longer ranges.