Don't get it sand blasted go for ball peening, ball polishing or tumbling.
Tumbling will give a beautiful flat polished surface.
The alloy is very very poor quality and will not anodise in any colour you like unless you want a very washed out look.
Some rifle reloaders will have a tumbler big enough for your chassis.
Also be careful of powder coating the inside of the inletting as the action may not fit as the tolerances are close and powder coating is a filler of gaps.....
If you need help getting it tumbled let me know