Hey, shill, remember how all those other firearm restrictions implemented in the US were immediately enforced with no grandfathering? Like when the Clinton AWB was passed and they suddenly required everyone to turn in all the "eeevul black rifles", standard capacity mags, and so on?
Oh wait, no, they grandfathered everything in circulation because Feinstein (who through stereotypical liberal hypocrisy has a CCW permit for herself), et al, couldn't summon the votes for a retroactive ban.
Same thing applies here: what's in circulation will be allowed to be sold.
What, are you 12? I presume you can grok the implication of a forward ban. Hell, you probably bought the ammo with the intention of scalping it once the supply dries up.