My first 243 barrel was pulled at 1400rds when I could no longer adjust charge weight or seating depth enough to hold 1/2 moa groups.
My current barrel at 1100rds fired, I just redid load dev and required the charge weight to be increased from 41.3 to 42.3grs of H4350 in order for groups to tighten back up. The trick I've found with the 6mm is when accuracy starts to fall off it's best to chase velocity through increasing charge weight then make minor adjustments if need to seating depth. I've found 3025fps-3100fps to be extremely accurate nodes.
Mind you I shoot my barrels primarily in matches and we shoot pretty fast with the barrel not getting time to cool for every string.
If you baby it I would and are running it single shot I would say any where between 1500-2000rds depending on your requirements.
I'll be putting it on the chrono this weekend to see where my speeds are after this recent charge weight adjustment.
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