Why chip with acrylic paint over acrylic base coat?

Have you tried salt chipping by chance ? 

Thank you Bish.  It certainly needs practice to get the scale and shape right so it doesn't look painted, plus knowing when to stop. Chipping fluid is great but not the same control or ability to vary the intensity of the scratches (a lighter shade of the base coat/primer/bare metal)

I think its mainly down the the colour options. When useing oils for weathering they do not need to be colour specific. But the chips require a certain colour to show through, such as the bare metal or a previous colour or primer underneath. I don't add chips often but when i do i use acrylics or enamels depending on what colour i need.

Depending on your subject, i would not worry to much about chipping as IMHO its largely over done and more of an artistic effect, unless of course an artistic finish is what you are after.