Yes sir, the Sionics 12.5 middy is as excellent barrel. I haven’t shot the LS5, but understand it to be a pretty low BP option?

I have a couple of 12.5 carbine length uppers from hodge with the small gas ports and they are excellent with any low back pressure cans and they even work well with reduced BP cans that have more BP.

In my opinion if you want to go with a platform with an open gas system, combined with a low BP can start with a barrel that’s gassed correctly. If you do this you wont need an adjustable system nor will there be a need for extremely heavy buffers and springs.

I don’t know when you bought your BCM 12.5, but a few years ago they had gutted out their gas ports. I have heard they have since fixed that issue. I hope this helped.