6br is truly happy with all weather safe load, aka soaking wet rifle/ammo in the mid to low 2700s with 26in barrel. A 6gt will get close to 2900 in same conditions. I have a 28in 6br running 109s at 2810-2820, it not very far from pressure, but my 28in 6gt runs 115 dtacs at same speed a mile away from pressure. The gt is almost 20% more capacity.
Feeding: 6br would work in hrd kitted ax mags or a gray ops br aw mag.
My 6gt atx will run from ax mags if I can keep all the rounds slid ahead in the mag, modifying a hrd kit spacer to 0.250 will do this, or run the grayops gt mag(which is too short if you're running 170fb chamber and long ass bullets like a 112 Barnes, 110 atip/smk. The gray ops mag work for most the short freebore loads, or 115 dtacs jumping a long ways in the 170fb chamber.
I'd suggest just going Dasher, and form all your lapua 6br and be done. Dasher isn't far behind the 6gt.
6gt is a good cartridge, I've burned out a lot of them, but the br variants are so accurate and load development is minimal to none.
The advantage of gt is generally feeding very easily from lots of different mags, plus a lil velocity boost over dasher. However, you're running a proprietary rifle with its own special mags, kinda takes that factor off the table.
