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Sanding Scratches showing through base coat

Here's the story:
Shot 3 coats of build primer on sandblasted parts.
Waited 36 hours and then guide coat and wet sand with 400 grit to remove guide coat.
Today I shot 3 coats of SPI Dark Red base and now it will sit overnight before clearing. Problem is I can see the 400 grit sanding scratches.
Normally I finish to 600 grit wet but since it was a solid color I thought the 400 would be fine.

What do think caused this?
Do you think the 400 grit under solid colors is not really failsafe?
Should I wet sand the base with 600 and then shoot another coat or two?
Not a pro, but sounds normal. I used epoxy reduced 50% as a sealer over 320 grit scratches, and I could see the scratches as well. They should disappear when you clear it.
If you blocked it like you would filler in a cross pattern those scratches seem to show more so then just sanding in straight lines. even with a 36hr dry time it can still be soft underneath causing the 400 to dig deeper leaving excessive marks. I will block the guide coat and shoot 1 or 2 more after allow that to dry and use a finer grit like 600. The first coats are still kicking off and tightening up the second layer of coats will help with hiding any shrinkage issues from showing.

If you did body work and primed once, blocked and painted in that time frame in about one month after the job is finished the likely hood of seeing sand scratches in the repaired area is pretty good. If you reprime and sand then paint you greatly reduce the likely hood of that happening.

As you sand the first coats you open the surface and allow it to breath out. It takes longer then 36hrs to truely fully cure out. If you sand it and can still smell fumes it is still doing it's thing. That is why if I'm doing something special I will prime something and forget about it for awhile and work on something else even if it means just taking a break.

You should be fine with a solid color but that would be up to you the smoother you can make the base the more pop you will have when cleared.
The only time this could possibly be an issue is if you were going to go with just two coats of clear, but I think you will probably do more, so those scratches will be just a memory soon enough.


Garage hack at night.....
Wouldn't worry about it with a solid color. With no sealer, base-coat will not fill 400 grit scratches if applied properly.....so that being said, you are good to go. Once you clear you wont see anything.
I just finished a 68 Camaro-hugger orange. I always finish with 600 but this time I decided 400 since everyone here says it's ok with a solid color. Shot the base coat and the sand scratches scared me ! but I stuck to what I read and shot 4 coats of clear....sand scratches gone !
on some parts I have blocked primer with 220. as long as its a med to darker color solid base then its all good when you clear it
Here's the part with a new emblem being test fitted.
Not sure if the SPI Dark Red base is making the emblem look orange or whether it is supposed to be orange?
Thinking I should paint the emblem to match the base but not sure. Any thoughts on that?
Don't paint it the same color! It should be more brick/adobe kind of red, at the very least there should be some contrast.

Come to think of it, blue might look cool if you are deviating from stock in other areas. If it should look original, there must be someone out there who knows what color they were when new.