I like thinking out of the box, sabots are one way of gaining velocity.
9 mm in AR 15 is one of my favorite calibers.
I run light 50 gr deep HP copper bullets with a small driving band to achieve high velocity.
I run over 2600 fps with 50 gr copper Hp in 9 mm AR with excellent accuracy.
All ten hits out of 10 tries at 205 yds with a 9mm. 115 gr at 1720 fps.
Or 358 win 16" AR top velocity was 3840 fps with the same light bullet, working up load, but accuracy was around 3750 fps.
Bearing surface has less affect than COAL.
Deep seating really spikes pressures in small capacity cases, much more than bearing surface.
I've shot 50 gr to 185 gr modified 200 gr .358 bullets in 9 mm...so ya learn those things through experimentation, and altering or making bullets...I prefer altering.
Lee factory crimp die can make a difference in your AR loads with a moderate crimp.
A balanced cartridge can achieve single digit S/Ds and excellent accuracy in AR loaded on a Dillion progressive, without any case prep, or even newly formed cases, & Lee factory crimp.
Super or sub new formed cases loaded on a Dillion progressive no case prep, case activated powder measure.... all loads in single S/Ds with excellent accuracy.
High load density and 100% burn in sub or super.
Long bearing surface short bearing surface it didn't matter. Light 160 gr to 350 gr all single digit S/D with excellent accuracy...even with factory 300 gr SMK 2nds and resized pulls.
Enough pictures to get the idea...all loaded on a progressive with no case prep, new brass, or formed 10mm mag pistol brass cases which had the ID champhered, no annealing, then ran through the Dillion progressive with Lee dies.
