Enforce What?

[JMBD2112]

If doing this before 01JUL13 - NO
Not unless you drove through a state that has them banned (such as NY; note- I'm not implying that you might go through NY, just using it as an example).

If doing this on/after 01JUL13 - YES
The bill also says you must own and maintain continuous possession of the mags being grandfathered in.
Note: Continuous Possession is not defined in the bill
In a case where you own them, and they are located in TENN, and you try to bring them back after 01JUL13, you MAY have not satisfied the "maintain continuous possession" clause.

That's what I was getting at, but unless they catch it in transit, they couldn't prove it other wise