300 PRC Initial Load development, Looking for input.

[Lovellr653]

Hey Guys/Gals, I'm looking for your input on the data I've collected so far, as you'll see I managed a couple good groups but can't figure out a rhyme or reason to them. I gathered my velocity data using a basic chronograph at 10' and plotted on a line graph a few different ways looking for this "node" everyone talks about. My inexperienced eyes are giving me inconclusive results. I'll also note I am not a great shooter and this is my first time working with a magnum rifle/cartridge. There's already a lot of material but i can provide more background if requested. Here goes...

Rifle Info:
Christensen Arms MPR: 300 PRC, 26" Steel Barrel (I believe 1:8)
Vortex Razor HD Gen II 4-27x56
Atlas Bipod

Load Info:
Brass: Hornady, once fired, annealed
Primer: GM215M
Bullet: 225g ELD-Match
Seating: 0.030" off lands
Powder: Retumbo (I started at 75.0gr and worked up to 79.0gr in 0.5gr increments)

This chart shows the 3 shot velocity average for each charge weight

This chart shows the 1st shot velocity for each charge weight

This chart shows the 2nd shot velocity for each charge weight

This chart shows the 3rd shot velocity for each charge weight

Cycle 1			Cycle 2			Cycle 3
grains	Velocity			grains	Velocity			grains	Velocity
75​	2693​			75​	2693​			75​	2710​
75.5​	2726​			75.5​	2726​			75.5​	2726​
76​	2749​			76​	2737​			76​	2743​
76.5​	2766​			76.5​	2766​			76.5​	2754​
77​	2777​			77​	2766​			77​	2766​
77.5​	2789​			77.5​	2772​			77.5​	2818​
78​	2824​			78​	2818​			78​	2818​
78.5​	2867​			78.5​	2849​			78.5​	2830​
79​	2867​			79​	2898​			79​	2898​

At 79.0 Grains I got my first signs of pressure in the form of light ejector marks on the case head.

Provided pics are of my two best groups. The first being at 76.0 grains and the second at 78.5 grains.

76.0 grains

78.5 grains

Thoughts, opinions, constructive criticism, questions....Any input is welcome.