Stick with your 12.5 arm. It is v good.
I used to own the 12.5 with tnt5 hr, then moved to hrx with 12.6. I much preferred the 12.5. Damping trough is required imo.
I used to own the 12.5 with tnt5 hr, then moved to hrx with 12.6. I much preferred the 12.5. Damping trough is required imo.