Just curious if anyone blasts an AR lower/upper with ALO3 before anodizing as a regular part of their process.

I just did a lower blasting at 40psi with 120gr to mat the surface and it seemed to make more uniform the black smutting when it was in the NaOH. I noticed on 3 earlier lowers the smutting was not very uniform. I made sure to degrease  with Greased Lightning, dish soap and a soak in acetone before and after blasting. It could also be because I used acetone this time and not previously as well.

I'm going to Gunkote and my goal is to have a good surface for the Gunkote to stick to. I don't use a die or seal in a hot water bath to keep the pores open.

It's interesting to see how the metal seems stained and the smutting process did not remove it. I noticed similar with the other 3 lowers but not as pronounced as this one. They are from Tactical Machining made from 7075. Anyone have similar staining on their Al pieces after anodizing? Maybe I'm not smutting long enough. I leave it in for 2-3 minutes.

I've seen similar striations in several lowers after anodizing. It's not your process, it's the forging. I etch for less than 1 minute and same for desmut (unless tanks really cold). I blast with 80 grit Al Ox. Makes a surface indistinguishable from type III mil spec commercial lowers/uppers. I've used glass bead but it comes out far too smooth.

It does look like material flow producing a grain in the metal.

Finished with Gunkote