Greschner,
Do you understand anything about our legal system?
Are you able right now, not tonight or after you run to the bank, to prove that you own your car? Can you prove you are in your home lawfully? How do the police know you have a right to be in your home? Seriously. The obvious answer is that you don't have to.
Our legal system is based on some pretty basic principles. Here are a couple.
1) if an activity is not explicitly prohibited, then it is allowed. - Think about this the next time someone on a gun forum says something like "Show me where it says that you can. . . . ". In that case, there probably isn't anything saying you can do something. Its the absence of something saying you can NOT do something that is relevant.
2) It is NEVER your responsibility to prove that something you have is legal. It is the prosecutor's responsibility to prove that what you have is ILLEGAL.
If you are at a point in your dealings with the Police where they are investigating the capacity of your magazine, then you have already been arrested or have been involved in a defensive shooting. To this end, the U notch mags make sense for carry. There is no debating their legality. Everyone knows this. Including prosecutors.
So you can carry your 10 round Glock 17 if you'd like. But don't give people bad advice.
If you own a Glock for self defense, either in the home or outside the home. There is NO reason not to own U notch high cap mags.
Have you ever been directly involved in a criminal case - either has a plaintiff or defendent? If you have, then you haven't learned a thing about what really transpires in "our legal system".
So as an example (which has cited before), let's say the police, fire department, and EMT is summoned to your house after a 911 call because (hypothetically) your wife is having a potential heart attack. They all get to the upstairs bedroom to address your wifes needs and - low and behold - the police officer (who always hated your bother - your entire family for that matter) sees a glock unattended (not properly secured) on the nightstand with a large mag protruding and asks:
Officer: I'll overlook the fact that firearm was not properly stored with all th excitement, but I noticed that firearm has a magazine that is carrying more than the 10 rounds. You realize the maximum allowable number of rounds is 10.
Husband: Well .. actually Officer, that magazine is considered "preban", so actually it's legal here in MA.
Officer: And how do I know it's preban"? You certainly must have records, receipts, or the mag itself must have permanent markings displaying as such.
Husband: Like most prebans, they don't have distinguishing characteristics, but you certainly can tell by the "wear and tear" that's it's pre 1994.
Officer: So let me get this straight, you have a magazine holding 15 rounds and the only proof of its legality is that it looks old? I'll tell you what, I'm going to take this into evidence (along with all your other firearms and accessories) and make our own determination. And, my advice, for good measure, would be to consult with an attorney. Oh, and, good luck with your wife, the cardiac catherization lab is fantastic.
So, yes, after 9 months of anxiety, loss of work revenue, and 30k of legal expenses you have been exonerated.