AR-15 Magazines

To my understanding in CA it is legal if it is welded to 10.

To my knowledge, it depends on the state.
Some specify how the magazine is now, some may specify how it was originally made, and in most with any restrictions you can't bring it in at all to work on yourself.

Hello fellow New Jerseyan. Here in our wonderful state of glee, we must have our magazines permanently (Read again: permanently) blocked at 15 rds. This can not be done in state to my knowledge; having a magazine that can hold more than 15rds in general is a no go so you wouldn't have any to modify. My suggestion is to check out http://midwestpx.com/index.php?cPath=15 they have a variety of 15rd options. I like the 20rd body so I have something to hold onto. The Magpul's also have a dot matrix that you can use a silver Sharpie to mark as 15rd (Although little good that'll do you if anyone challenges it)

The floorplates are pinned in place on mine, but there are options for magazines cut to 15rd size, which can be disassembled for cleaning if desired.

However, to answer your question, no it would not be legal to only install a limiter. It would however if the limiter were in place and the floorplate permanently attached via welding. Basically the mag can't be disassembled so you can't rebuild it at a higher capacity.

One possible solution, if your employment is close enough to allow this, is to move just across the PA border.
You can buy all the 30 rounders there you can afford.

It was never challenged anywhere, but one of my shooting buds who'd go shoot high power matches in Jersey took some 20 rounders and pop-riveted the bodies on some to make them not accept more than 10.

The limiter would have to be permanently installed. Also you would have to do the limiting outside the state since you would still be in possession of a standard-cap mag before you modify it.

One possible way for you though is to buy a mag "parts kit" those are just magazines disassembled into their individual parts. Order it to yourself in NJ, modify, then assemble into a working 15rd mag.

Most places will ship the parts kits anywhere you want since they're not "magazines". They're "parts".

Though I don't know about the exact legality of ordering a "parts kit". Wether it's truly legal or just "legal" due to being unenforceable.