I'm helping a friend build a rifle using a BCM 14.5" midlength upper. He has it in his mind that he wants a rifle length buffer system for reliability. I suggested the Vltor A5 so he can at least have a shorter LOP. My questions to people that use this combo are: is this necessary? and if so, what weight?

I ask if it's necessary because I know the BCM 14.5s are relatively lightly gassed and the Vltor A5 system seems more beneficial to overgassed rifles. I ran one on a KAC SR-15 for a while, and while it changed the recoil impulse, I wouldn't say it improved it and I have since gone back to the carbine buffer system.

If he does stick with the A5, what buffer weight would be recommended for it? I'm thinking the A5H2 may be too heavy for a rifle that's already lightly gassed. I'm thinking the A5H1 or A5H0 is more appropriate. What is everyone else using?

Oh, and diet will be various brass case .223/5.56 but no tula or other steel case ammo.

I'm pretty positive my DD 14.5 mid length is over gassed compared to a BCM. I run the "standard" A5 buffer which is the A5H2. It runs and doesn't have any issues with weak ammo like Tula, PMC bronze, or Wolf.
Worse case scenario Heavy Buffers sells a weight kit where you can virtually make any weight combo the A5 offers to see which weight the rifle likes. He can always start with the A5H2 and flip it if it's too heavy which I really doubt.

I ran my old EAG upper with a standard A5 buffer.  It would also run fine with the A5H3 and Federal .223.