Zbros arms are stronger than they should be imo... the only arm on the market that will damage your sled over breaking the arm. No thanks. They make a ton of good stuff, but the M 40" arm isn't one of them IMO (and I'm not selling anything to compete with them)
BDX will likely not have A arms any time soon in the 40" length, so that is not CURRENTLY an option. I'd go alt impact CrMo.
Good to see you associating with us non-crazies from time to time Slut!!!
If by some chance you're running HCR arms (I was pretty sure you're running a regular M, but I could be off) & want to stay with that width, I'd be happy to help you with BDX ones, just not the 40's.