The upgrade they sent me for my .40 JR is a buffer tube extension, spring, and buffer, a white(compared to the old back) bumper and disk.
Interesting.
Also a feed ramp, mine had none but did have the cut out for this one to screw into.
They also sent me a new charging handle and a screw for it that I stripped.
I put 50rds through my .40, winchester 180grs factory stuff, and had no issues.