223 vs 6.5 Grendel

[rgv]

All within SAMMI specs right?

Nope. My high tech load development consisted of shooting some black hills Mk262 over a chrono and then loading enough TAC to push a 77 to the same speed.

Hornady 75 grain TAP sold as 5.56 clocks in the high 2800's as well

 

[beltfed]

I think if you are looking to load into the lands of a Wilde chambered rifle and want appropriate neck tension, you are likely going to go after an 80 grainer or longer bullet, the exception being the Berger 75 VLD as it is a fair comparison to the 80 SMK (in overall length).
In my 24" heavy barrelled AR, the 80 SMK mics at 2.480" the 80 Berger, 2.420" and the 90 Berger 2.545" OAL touching the lands.