jdubrr
Lil-Rokslider
Not sure the OP will like the CA as it is also limited by the mag length. I just got the Ridgeline in 300 PRC and I just started load development with Hammer 214g bullets. Can't load them .020 off the lands unless I hand feed each round. I guess you can keep one mag and one in the chamber and if you use a 2 round quiver you could access additional rounds somewhat quickly.Christensen arms in 300 prc will be a solid turnkey set up with the right mag length and twist.
But yes custom is the way I'd go
Christensen arms are 8 twist in 300 prc