I have several grips from when the P320 was first released and a current generation P320X. I tried putting the FCU into one of the older grip modules but it didn’t quite want to fit, primarily when I was trying to insert the takedown lever. It just wouldn’t quite seat all the way. Should this be working or is it a no go? I prefer the small full-size older grip to the medium fullsize that came with the gun, plus, I have a lot of older mags that won’t seat in the new grip.

The FCUs should though sometimes they need a little finessing. I had to do some tappity tap tap with a little mallet to get it in right.
As for the magazine there are two different baseplate designs. The older ones with the words Sig Sauer and a round hole won’t fit new grip modules.
The new mags have the Sig logo and a square hole.

Make sure you push the FCU all the way back (towards the grip), and then push it down in the front (adjacent to the Take Down Lever bore) in order to fully seat it in the Grip Module. Some times the FCU will kinda 'snap in' the tighter Grip Modules when it fully seats.

I agree, I changed mine out to a Lima Grip with laser and it was tight.... I think I actually put it in a vise and forced it in, probably over kill. But I have no desire to try and remove it now and so that kind of defeats the idea of being able to move it from one frame to another.... which I never really got anyway other than being able to buy slide barrels and even the grips without dealing with an FFL.

quote:

Originally posted by nhracecraft:
Make sure you push the FCU all the way back (towards the grip), and then push it down in the front (adjacent to the Take Down Lever bore) in order to fully seat it in the Grip Module. Some times the FCU will kinda 'snap in' the tighter Grip Modules when it fully seats.

I think this was the problem. I took it back out and started over again and managed to get the take-down level to seat all the way through on the second attempt. It def is a little tighter than grip came with, and as mentioned by another poster, my old mags now work with the pistol while the grip is FAR more comfortable to me.

Function tested with 3 mags and I’m good to go.