For those that own a 9mm 2011, what problems are there in procuring and using the magazines that are needed in NJ?

For some models, they seem to ship with 126mm magazines, and for those I know that you can purchase 10 round 126mm magazines. For other models that come equipped with magwells, they ship with 140mm magazines. Would the 126mm work? Would you have to buy extended basepads? Or would you have to find a source for altered 140mm magazines?

Ideally, I would love to find a source for 15rd, 126mm and 140mm mags, but not sure if thats realistic.

Try calling RTSP or World Class Steel.  Both are STI vendors!

Contact Brazos as they do custom work with STI guns. Or, contact STI itself.

In general, the 126mm, 10 round mags function fine with the stock STI magwell. The only issue is that they don't protrude from the magwell so positive seating means recessing them into the magwell. You can get base pads that will extend the length but you have to be careful on what you buy. There are some extended length, no extra capacity options like the STI "international" pad - its a simple wedge shape that makes it somewhat flush with the mag well. On the other hand, there are extended length, ADDED capacity pads that can be used, (such as the Dawson tool-less pads) but you have to address the added capacity thing. Not so much for legal limits, but for functionality. They add much more length for positive seating, however, the cavity inside that would normally add capacity is going to be a nuisance for this style of mag. The 10 round mags are essentially a single stack design and so you cannot use the double stack mag springs which leaves the original spring a little short for the added capacity inside the extension. Folks will often fill the void with something (epoxy, polymer block or even 6 9mm cases stacked up neatly - im not kidding!). This will allow the spring to seat in its normal base position for tension purposes, and prevent the follower from going down inside the base pad cavity.

Dawson makes base pad extensions that are not capacity increasing. They work nicely with the STI mag well. 

 

http://www.dawsonprecision.com/ProductDetail.jsp?LISTID=8000005B-1388517800

 

I have several. If you need them live with silver. I have had black ones on back order for well over a year now.