What size grip module comes standard on SIg p320X Compact? I feel like I need to get a larger grip. Their site shows SM, Med, large. The issue I am still having is that sometimes the slide lock back while rounds are in magazine. I change slide release to a lower profile one. Still happens.

The Medium comes standard on the gun.

As 12131 said, the X-Compact comes with a "Medium" size grip from the factory. I bought the Large size X-Compact grip frame and honestly couldn't tell much difference in size. I ended up buying the Wilson Combat X-Compact grip frame and I am happy with the larger size.

Don't know anything about the X and whether this applies. Will post anyway.

I have a P320C with the standard Sig OEM M grip size. Bought a WC Carry to replace it. The circumference is smaller, but the contours are far better (IMO). Feels like it was made for my hand.

I "measure" circumference by where my thumb tip positions in relation to the middle finger. Thumb tip farther forward on middle finger = smaller. Farther back = larger.

Have a P365 XL WC grip also. All I can say is that the Wilson grip appear to be designed by shooters. Hard to verbalize, need to actually try/shoot one.

OP, any chance your thumb is hitting the Slide Release Lever? Have somebody observe/video you and/or try shooting with left hand. Defective SLR? Might not be a grip size issue.