While we are straying off-topic, I would agree that the number is well into the hundreds of millions. Even the onerous 1994 federal ban still allowed possession and transfer of existing standard capacity magazines. Unconstitutional state level restrictions notwithstanding, there is no way for the federal government to practically outright ban standard capacity magazines.
And remember, we have none other than the late William Ruger to thank for the arbitrary “no honest man needs more than 10 rounds” mentality among the hoplophobes.
Sometimes we are our own worst enemies.