The Scar gas port thread got archived, so starting a new thread that's hopefully of use to someone. Here's my results with a new (less than 50 rounds) Scar 16 with factory 10" barrel unsuppressed using American Eagle 55gr .223 ammo. Used the slo-mo setting on my phone, marked the end of the charging handle with a silver sharpie, and the receiver at bolt hold open and max travel which is about 25mm past BHO. Photos are the max recorded travel of a few rounds with each port size. For the time being, I'll be using the 1.60mm port, which is smaller than what's often posted elsewhere on the internet. I'll try it suppressed in the future. If my forward grip looks funny, it's because I'm holding the remote to trigger the camera.

The 1.45mm port wouldn't lock back and falls short of the BHO mark...


The 1.50mm port would lock back and barely clears the BHO mark...


The 1.55mm port clears the BHO mark around 10mm+...


The 1.60mm port clears the BHO around 20mm+...


The 1.65mm port hit max travel in 2 of the 5 rounds fired and the remaining 3 rounds were very close...

I like that technique. I need to tune my 20s with both the 7.62 and 6.5 barrels. I was just going to drop the port size until it stopped holding the bolt open with a full mag but I like your way better.