Your current CBTO measure is less than the saami freebore measure for the 6.5cm (2.140”) so very good chance the bullet is getting hung up at the chamber mouth or in the freebore region BEFORE the lands (throat region). Two ways I’ve run into the same issue are (1) dirty/carbon fouling…rifle...
+1 on 64g Nosler BSB. Loaded warm under n540. 60g partition or mono in same class. SPS runs sales on the BSB occasionally where I picked them up for $0.25-$0.30ea. 3/4 moa w LC range brass. Hits very hard.
I've had good luck with the 100g PTs and BTs. Currently running 100g PT over 29.2g XBR with a Rem 7-1/2. ~3/4 MOA or so out of an 18" larue upper. I found my gun liked the noslers better than hornady bullets and the 100g class over 120g (shoots 3/4 moa vs 1-2 moa with the 120g or hornady...
Excellent accuracy in my ‘06 with 165s and IMR4350 using Nosler’s “max” load (which was under max but very accurate for me)..suspect you should be able to achieve similarly with H4350. I would work up from 55 up to ~58 grains if you go that route with the H4350
Awesome bull! Congrats all around.
What powder did the 123ah like in the 6.5cm? I've got some on the shelf, and you provided inspiration for me to start toying with them.