Accuracy Issues

[THE300BLK]

I’ve got a 20” Grendel Hunter 6.5 Grendel upper and finally got ahold of all the necessary reloading components and I am trying to develop a load and it’s off to a HORRIBLE start. I’m shooting nearly 3”-4” groups at 100 yards! I’m definitely capable of shooting tight groups and have shot cloverleaf groups out of this gun with Federal Fusion 120 gr SP, but my current quest to find a tight shooting load is rendering more than disappointing results. Due to lack of availability of reloading components, I’m limited to Ramshot TAC and 123 gr Hornady FMJs and SSTs. So far, I have loaded everything from min to max load according to Sierra load data and my tightest group is still over 2.5”. I’m using brand new Starline brass and CCI small rifle primers. I can’t believe that ALL of the loads in the Sierra manual for TAC would be that inaccurate. I thought TAC was supposed to be a very accurate powder for the Grendel. Am I missing something???