Will I need an adjustable gas block on a 12.5" pistol build?

[jurassic]

You will have to figure it out with your gas system, loads, and recoil system.

Most people open the port for that length. I would try it first before messing with the port. You also will do yourself a favor by finding a way to seal the gas block and tube off from gas leakage. That will allow you to use a smaller port and no need for adjustable gas.

I would recommend having at least those 2 buffers on hand, or using a JP SCS.

Thanks, I usually use green loctite on the gas tube at a minimum, but I'll run it first.