Re: 77 gr psp loads for .223 cal
For 77 gr. SMK and Nosler CC and Hornady 75 gr HP match; 25.5 gr of RE-15 for the 5.56 and 25 gr. for the .223. Velocity out of my 16" 5.56 is 2690 and velocity out of my 26" .223 is 2990. Twist in the AR is 1-8", twist in the .223 is 1-9. Extra velocity may help with stabilization there.
That powder is relatively dirty in my AR. But, it gets good velocity.