Magnum small pistol primers in .40 cal?

[NW-GSP]

I grabbed them by mistake and primered about 300 cases and then noticed my mistake.
I have not loaded any of them yet due to worrying about something bad happening.
Can I just lower the powder charge by a grain or will that not be enough?
I am using blue dot powder and 180gr jacketed hollow points

[Ash]

Go back to starting load levels. I would avoid using them with quick burning powders, like TiteGroup and it's likes. Blue Dot should be OK. You should be fine, other than having to redevelop your load.