Shortening the bullet count in a magazine isn't going to stop someone from shooting up the next school. A gun is a one hit one kill in real life, this isn't a video game where you need to empty 1/4 of the magazine into someone to kill someone. You can carry an extremely powerful handgun too such as a .44. Assault rifles only differ from pistols due to the fact they're fully automatic and can carry a larger magazine (standard.) Even then this doesn't stop a pistol from becoming automatic or burst.
This doesn't stop people from owning assault rifles anyways, if you have a decent amount of money, you can buy them from a non-official vender. Illegal but it's not like you're going to buy them from someone walking off the street.
Congress, House of Representatives & The President can't assume that 10-round magazines will stop someone from killing someone else, even if you ban those (which would most likely start a national protest), people will resort to melee or bows/crossbows.
If congress were to vote the executive orders into law I will hate this country more than I do now.