So I'm looking to send my barrel off to Class 3 Machining for my chop. Quick question I have is what is the optimal gas jet size for 10"? Unless my google-fu has failed me, I can't quite get a good bead on an answer. I have a class coming up and I will be running some 55gr wold golf if that matters any.

i picked up the tuning pack from handl for my 10 inch 16.  they recommend the 2.25mm screw for the 16 but mine was way over-gassed with that one.  
i found the 1.80mm was 100% functional suppressed and unsuppressed with both 5.56 and .223 ammo in my rifle, using the correct gas setting on the regulator.

You can get individual gas screws here: http://www.midwestgunworks.com/mm5/merchant.mvc?Screen=CTGY&Store_Code=mgwi&Category_Code=scar-parts&view_perpage=all

It's pretty easy to set the SCAR up like you would a FN FAL: Start with the smallest gas screw, put a single round in a mag, and then fire. If the bolt doesn't lock open, move to the next larger size of gas screw and repeat. Once you get the bolt locking back on an empty mag, go up 2-3 screw sizes for a little insurance.

AJ

I started with a 2.0mm, and went down to 1.9mm.  Works with both 5.56 and. 223.

With my 10" SCAR I started with 2.0 and worked my way down to 1.8, works perfect suppressed and unsuppressed with all ammo.