rifle build, can it get better?

[Retusmce7]

i have a remington 700 sps in 300 ultra mag. shooting 180 grain barnes tsx bullets groups 1 moa at 200. i had timney trigger added to the rifle and now im thinking of having a custom barrell put on it. i have heard from some at gun shows and talks in shops that the stock 300rum barrell will give me problems and that there is a rather large gap in the necking and that i should either replace the barrel to my custom loads or have the barrell trimmed.
I seek you expert advice
i would realyy like to find someone i could send it to and they make it right. i know it hits well i did drop a hog at 600 and a deer at 700 but accuracy is getting addictive and i want a true 1000 yard gun