Howdy! Well if you are reading this, then I take it you or someone you know has a SIG P320 that may be using the P320 21 round magazines for their pistol? Then hello there fellow SIG fan! Great choice in a gun, if you don’t mind me saying!
So on to the meat and potatoes.. If you are still reading this then I assume you read the title and you have an interest in participating in a USPSA match possibly with your P320, or perhaps you switched to these particular magazines in which I am sure you are excited about the reduction of reloads you will experience in the upcoming matches, but which has led you to stumble across this question.. “Are my 21 round magazines compliant?”…
The short answer… “maybe”?
I know this may not be what you want to hear.. “Marcee just tell me already!” Well I don’t know for sure if your mags will fit the USPSA length gauge which is what will be checked prior to starting the match. Your 21 round mags might vary slightly then mine, and then can also vary slightly from your friend who has the same factory magazines. So the best answer to know is you will need to test your magazines in an Official USPSA Mag Length Gauge. You can either measure these at your next USPSA match (I don’t really recommend this unless you bring back-ups just in case), borrow a friend’s gauge (if someone you know has one), or you can just purchase one yourself! I obtained my very reasonably priced Official Mag Length Gauge from Dawson Precision here. What better way to rest easy knowing if your mags are USPSA complaint then to test the lengths yourself!
As you can see in the photo above, my mags didn’t fit the gauge exactly flush to where they needed to be. The baseplate lip forced a raise on the left side up just so slightly that it did not seat flush in the gauge, until I modified the baseplates enough to have them fit. If you wish to modify yours like how I did as well, all you need is a sander or Dremel and take off a few millimeters from the lip of the baseplates. By the way, ladies, if you would like further video instruction on this, take a peak at our Ballistic B.O.S. Women’s Brigade of Shooters Community Group here where I show the ladies in the group exactly how to shave off their own baseplates to help fit the gauge.
If you do not want to modify your baseplates this way, you do have other options like removing the factory baseplates completely and replacing them with new machined, compliant baseplates such as the ones from Springer Precision that can be found here. Springer Precision makes high quality parts and accessories with the shooter in mind. I highly recommend you take a look at what they have to offer.
If you do not wish to modify nor switch out your baseplates, you could simply use the SIG P320 17 round magazines, since in most all cases, these will also fit your P320 and of course will fit the mag gauge with no issues. You may need to reload more often with the 17 round mags, but with sufficient reload practice, this can still create a smooth and fast match outcome. (Pssst… ladies.. we also have a whole “Reload Retreat” in our ladies community. Super valuable info available right at your fingertips!)
To circle back to our main question.. seek your answer by measuring your mags properly and proceeding with whichever direction makes the most sense for you. I found shaving the baseplates was the easiest, quickest and at really no expense for me. If you choose this route too, let me know and if you have any questions, please do not hesitate to reach out!
Happy shooting my friends!