What size drill for autogun barrels?

[Space Truckin]

Any suggestions?

 

I would like to drill out the barrels of my DV Cultists and I'm not sure what drill size to order.  

No hobby shop here so I have to order online.

 

 The one I use for bolters (1mm diameter) is going to be way too big.

 

Thanks in advance!

 

EDIT ->  ok after more searching on the internets  it looks like .4mm is the way to go!