Read through a few previous threads on using Norrels, and found some good tips
My question is about sanding through some of the high spots to add wear.
Should I do this before, or after curing the finish?
Also, what grit blasting media would closely match the look and feel of the original anodizing?

Do any weathering after curing in the oven.
Before it's cured, the Norrell's is pretty soft and may come off quicker than you want it to.

True i did one like that , i baked half the time and the wear had a greenish/goldish finish.bake time affects color. Also i like to let it cure a day or two(or longer).

like the others have said do your weathering after it's cured.  i just did a lower and used 0000 steel wool on it.  





don't use too fine of a blasting media or you'll make the surface to slick , lower the pressure when blasting instead.  





the best way to get a smooth finish like anno is to spray right over it.  it's going to be hard to replicate it with norrell's.  don't overheat the parts before spraying or you'll get a "rough" finish.  a cooler part will yield a "smoother" finish but can be a bit trickier spraying the norrell's on.





the lower i did i sprayed 3 times trying to match a factory grey anno'd upper receiver.  the first time i tried the new semi gloss greyish black and didn't like it.  after 2 more try's with flat greyish black i was happy enough with it.  in hindsight i wish i would have just used the flat greyish black over the factory black anno the first time.

 

Thanks for more good tips gleaned from experience guys.
I'm going to give it a try in a week or two.
I will post pictures of my results, good or bad.

Remember that aluminum when exposed to air immediately begins to oxidize which will prevent the Norells from adhering well. Bead blasting followed by cleaning followed by spraying in as short a time as possible will improve your results. My experience though is that edges  always  chip exposing white metal. I love Norells for tinting already anodized or parkerized surfaces and the tuffness of phosphate is enhanced by the moly spray. Even though you are considering weathering the parts the end result will never be or look as good as anodizing.

Somewhere there is an echo of a Dad saying: Any job worth doing...

Yep, the Norrell's doesn't stick to bare aluminum nearly as well as it does to anodizing.
The lower for my XM177E2 likes to chip around the pin holes, even after sanding, scuffing, and degreasing the area right before spraying.

I ended up mixing some flat grey modeling paint to match the Norrell's for touch up. My receivers that were already anodized before being sprayed have yet to chip, even on the corners.

For my next build, I will be having the lower clear anodized prior to spraying on the Norrell's.