Quote Originally Posted by MadAngler1 View Post
Subsonic ammo needs more gas. It will have less back pressure. I am also using a HUX WRX OSS suppressor, so unlike my Surefire equipped Galil ACE, I won’t have the added back pressure of the suppressor to help with cycling subsonic ammo.
That makes sense. My brain was assuming an installed suppressor increasing the back pressure.

I emailed the company, and he does not currently make a 553R compatible valve. The 553R apparently has a different gas piston diameter from the 550/551/556 and 5.56 NATO 553s out there unfortunately.
I'm pretty sure that the 552 and 553 have the smaller diameter gas valve as well.