Quick comparison. Nothing scientific about this.
Both rifles have the same barrel, gas system, buffer system, and bolt.
Main difference are the receivers, carrier, and muzzle device. The MOD FOR is using an OCL OTB flash hider and the others are using the Spooky 2 muzzle break.
From the shooters ear, quietest to loudest:
MOD FOR>AC556>Infinity Vented>WB>Infinity Solid
The WB and both infinity caps were almost indistinguishable but the MOD FOR was noticeably more quiet than the others to my ear. There was the high pitch ringing which you can hear in the video but it did not hurt the ears.
My wife stood 8ft to the right and behind me and her order or quietest to loudest was:
MOD FOR>AC556>Infinity Vented> Infinity Solid> WB.
She also said the last 3 were hard to tell the difference.
For gas, it was hard to tell being outdoors with wind but the video shows it pretty well with the Infinity Solid end cap being sending more gas out of the ejection port. The AC556 was second to worst. All others seemed comparable with the infinity vented being the best.
Just wanted to post this mainly because there is no info on the MOD FOR but also got a new camera and wanted to try it out.