Not sure how raising the price of ammo, by instituting a national tax, will make anyone "safer".
Make no mistake, the ammo tax would be used to make ammo so expensive that few can afford to buy it. Sure, at first the tax be low enough as to only have a small impact. Long term however, I have no doubt that tax would continue to increase until it put ammo out of range of most people.
They can't outlaw guns, but they can make them useless. Any step the anti's take is a step towards the endgame of banning all guns from the common people.
Without ammo, a gun is useless, and "safer". The antis are counting on people accepting a small tax as basically harmless until that tax now elimates the ability to purchase it.
If people can't afford to purchase it, stores stop selling it and then stop carrying it so even if you can afford it, you can't find it. No ammo makes your gun useless and thus "safer."