I forgot to post a while back that there have been reports of the Bul Armory SAS II UL’s recoil spring assembly (RSA) failing. The rod usually comes apart.
There’s a fix. Folks have been buying 3rd party RSAs as standby RSAs for when/if the OEM RSAs fail. The 3rd party part is the EGW Colt Defender guide rod assembly, made by EGW.
Another option is the Kimber 3″ Ultra 9mm Recoil Spring Assembly – part number 4000466.
I bought the Kimber RSA, but have yet to test it by shooting. I’ve test-fitted it and it fits without issue.