The schuster (sp?) gas plug is exportable from Brownelles.... Little side note, Brownelles sells all the parts necessary to install a SAI gas system on your Nork rifle (and a NM tuned Gas system to boot) and schuster gas plugs.. Last I checked, it was around $200 USD for the parts, so a little paperwork and its on its way.....
I ordered one, it fits my SAI, not the norks.....
The idea behind them is that it increases the "dwell time" (the time it takes the bullet to exit the muzzle after it passes the gas port and induces movement in the gas piston) which in turn reduces inaccuracy due to movement in the rifle.
I have not actually installed the part on my springer, I'm still in the "accuracy testing phase" of that particular rifle..... But it is something I'm going to try once I finish tweaking to see if it shrinks groups.
Most guys on the U.S. Forums that use them, use them to reduce wear on their rifles and don't report big accuracy gains.....
I've had some "fun" with a couple Nork gas nuts..... Increasing internal volume (drilling out material inside the gas nut) as well as drilling a .040 hole in the gas nut to vent excess pressure....
I have a short "brush gun" (shout out to 45ACP) that really likes the gas plug with the .040 hole. It digests Hornady custom 165 gr hunting ammo with no trouble and is fairly accurate to boot..... Accurate enough, I took it as my back-up rifle to Elk camp this fall! The down side to the .040" hole..... Chi-com copper wash ammo will not cycle the action enough to pick up the next round. The Hirtenberger ammo only works 50% of the time. This is a very simple fix IMHO, I have one gas plug that is drilled, and one that isn't, depending on the ammo I am shooting!
Cheers!