The primer WILL knock the media out of the 'flash hole' with no problem when shot. This has been discussed and cussed on most every reloading forum out there.
Now then why not get the 20/40 grit media so as to not have the problem in the first place. You can have it shipped to your nearest Grainger for free and pick it up their. It also available from Zoro tools.
http://cart.zorotools.com/s.nl?sc=3&c=1326902&n=1&ext=T
http://www.grainger.com/product/ECON...26s_pp%3Dfalse