http://www.fbi.gov/about-us/cjis/nics/reports/total-nics-background-checks-1998_2013_monthly_yearly_totals-033113.pdfIt shows that there were 169,984,008 background checks since November of 1998, and 73,219,367 since Pres. Obama took office in 2008. Checks reached a peak in December of last year, at 2,783,765.
For this year the checks seem to be slowing down, which fairs well for ammo shortages:
Year Jan Feb March April
2013 2,495,440 2,309,393 2,209,407 1,714,433