About ready to throw in the towel

[milehipo]

Hello I have a new build with under 500 rounds
AR 15 300 Whisper Matchgrade Upper - Barrel length 10" 1:8 twist
AAC Cyclone Suppressor
RRA Lower Receiver Lar-15
20 Rd P Mags
Load:
9.1 H110
220 SMKHP
COAL 2.235
Gas block set for subsonic
After weeks of trying different powders, bullets, and brass, I have not come any closer to getting decent groups than when I started.
Shooting outside in decent weather(50degrees)with just about no wind.
Stable bench and bags
Scope,rings,and base are tight.
Suppressor is tight.
Triiger is 2-3 lbs
Do not want to mention the builder nor do I want to say any negative but they have been little to no help at all.
Looking for recomendation for a knowledgable 300 Whisper/gunsmith that I can send this off to.