Sig recently redesigned the slide catch lever and grip shell for the P320 and P250.
The new slide catch lever works with old grip shells but the old slide catch lever does not work on new grip shells.
Sig is shipping new P320's and P250's with the new style grip shell and slide catch lever. New Caliber X-Change kits are also shipping with the updated parts. We're seeing many new grip shells (but not all yet) coming in with the updated design. The updated grip shells do include the slide catch lever.
Download the installation instruction: http://www.osagecountyguns.com/media/ocg-sig-slide-catch-lever.pdf
Sig is not updating part numbers on grip shells, Caliber X-Change Kits, or firearms to designate that they are shipping with the updated parts. As a result, it is extremely difficult to segregate inventory in our store and warehouse. If you really want one or the other I suggest calling and speaking with our sales staff. We cannot guarantee you'll receive one or the other but we will try our best to accommodate your needs. I expect that once the inventory on the old style parts sells out we won't see that style anymore.
Below is our video showing the difference in the parts and comparison photos are below too.
See and order Sig's grip shells in our store.