Blaster paint problems

[BDR78]

Hey all

So I just spray painted my scout blaster with a spray can.

I had given the thing 2 coats of primer beforehand. It all looks great apart from the trigger guard which is aluminium started to blister immediately. Any idea why and how to fix this?

Thanks

[Chunk]

Sand the trigger guard, & wash with soapy water then rinse good. Mask everything off except the trigger guard & repaint.