To describe the "sanding down the nozzle" in another way...
Take a pencil in your right hand....eraser end pointed to your left hand.
Take you thumb and pointer finger of your left hand and "pinch" the sides of the eraser.
With your right hand...twist the pencil back and forth like you're sharpening it.
That's about it....but use a 400/600grit piece of emery cloth (wet/dry sandpaper will do) to pinch it.
You are not changing the nozzle tip profile/design/curves/etc...at all. Just reducing the diameter a bit.
I'll have to mic the stock one vs. RATech one again...didn't write down the numbers. It's not much at all really...but it does have a marked difference in action.
Basically you're aiming for the nozzle to almost just not stick at all. When you rack the bolt back (you can do it by hand by just grabbing the bolt carrier)...it will extend out the rod. Up until the end of the extension, the nozzle is still in the chamber. Just past the full extension of the rod, you'll have to give the bolt carrier a tug to free the nozzle from the chamber. If it's "stuck" then you're going to have inconsistent/wonky action. Basically there should just be the slightest amount of pull needed to free it. You want it to create a good seal...but not a jam tight fit.
Same again when chambering...the nozzle should go into chamber easily by hand (it will no matter what with a big recoil spring pushing it
). If you feel that you have to press the bolt carrier into place to seat the nozzle fully...it's too tight.