I know GAP claimed the GT to be THE fix for prs mag fed rifles. I personally feel a kitted aics mag with a br variant is prob more reliable than a gt from standard aics mags. I ran a 6BRA from non kittle aics mags for a season and had little to no feeding problems. There is a reason companies are coming out with GT specific mags now. If you want 100% reliability feeding from the ctr or non kitted aics mags, I'd chamber the rifle in 6x47, 6xc, or 6 creed.
I have shot out a number of 6gt barrels. My first was an Impact/xlr chassis, used pmags initially, then ARC aics mags. Mdt non binder mags were not good(early generation mags), did not like aw mags either. I've built some on ARC nucleus/archimedes actions, these all ran the ARC aics mags like a champ and still do. My AI ATX has a 6gt barrel and it works with AW mags, as does my Cous De Grace 6gt. The womans match rifle is a TL3, it has been using ARC mags but I recently acquired a few the Grey ops 12rd billet aw mags to test. The womans first 6gt was on a Tikka, it was in a bravo chassis running arc aics mags. I installed that same barreled action in a CTR stock and tested ctr mags, feeding was prob 80%, installed a standard Tikka T3 bottom metal with 3rd M mags and they all fed great for prob 30 Rd of cycling. Tuning feed lips is usually a necessity with any rifle for optimum performance.