It would be a huge stretch for anyone to argue that a Glcok with a standard capacity magazine or an AR-15 with a 30-round magazine is not "in common use."
I agree 100% yet you have Millions if not tens of Millions of magazines and firearms set to be confiscated, destroyed or otherwise displaced if the SAFE act stands, or if other states like NJ, MA, CT, CA, OR, MN, CO etc pass bills that have recently been proposed.
What will happen if say the SCOTUS says the SAFE act is unconstitutional ? What happens if CT or another state pass laws stating that you have to turn in all "assault weapons' and "large capacity magazines" to be destroyed?
Hopefully you quickly find a federal court willing to issue an injunction until things are not sorted out, but that is not a sure thing. If not it is doubtful gun owners will ever be "made whole' through any sort of compensation.