I think it was the standard PMC stuff. I don't consider it low pressure per se but understand where you are going. Hopefully with a little bigger hole, it will handle everything.
The adventure begins....
The PMC 223 ammo is definitely lower pressure than their 5.56 ammo. Same for Federal. If you tune a rifle to just barely work 100% with the 5.56 rounds, often it won't cycle completely with the 223 stuff. Yours may have ended up in that situation from the sounds of it.
Opening the gas port is still the best option regardless.
Tip for drilling the port (assuming you have at least a decent vise and drill press) - find a drill bit that matches your current gas port size, and set it in the hole when you clamp the barrel in the vise; that makes it easy to visualize when the hole is perfectly vertical.
Then to locate the hole, hold that same drill bit backwards in the drill chuck, inserted as far as it'll go. When the drill bit shank will slip into the gas port hole, you've got everything aligned correctly for drilling to the next size up.
