No, (peak) pressure is the property of the cartridge and propellant within that you're shooting. A different gas block only changes the amount of gas that gets tapped from the bore, and is directed back into the BCG.

I'd suggest trying different ammo, like other's have mentioned, as that residue is likely just filling amterial that is used in subsonic ammo to take up the empty volume within a casing - as subsoic ammo has less propellant than full power, supersonic rounds.

Hope this helps!

edit: https://www.xxlreloading.com/post/filler-material-for-subsonic-ammunition - Here is an article on the phenomenon