I know that we all test our EDC guns with the ammo we use in it at some level to determine reliability. For those that carry a P320 and who use different size grip modules depending on the situation. Do you go through the same rigorous testing with each grip module or do you ASSume that with the same FCU and slide that alls good?

One would think the performance would be the same, but they're not.

I have a number of P320's. I found that moving the same FCO between frames and uppers produced different results. In one case, I put the same FCU in a subcompact frame and upper, and tried it in a compact. In the compact it ran perfectly, but had numerous problems in the subcompact frame. I substituted other FCUs and could not duplicate the problem.

The original FCU did find and has exhibited no performance problems in a compact frame. The complete pistol went back to Sig for the upgrade, and has been 100% reliable without a hint of trouble since returning. My decision, despite the modularity, is to keep the components together and not switch them around. If something is working, I'll keep it that way.

I have yet to put carry ammo through my P320s for this very reason.

When SIG gets their thumbs out and sends me two Small Compact grip modules, I will run 350 rounds of hot ball followed by 150 rounds of JHP through both pistols and go from there.

I also have not switched slides and grip modules around from model to model. Darn caliber exchange kits are so hard to find and to expensive anyway.

While it may work, look good and be more CCW versatile, I think a specific model should probably stay in the configuration it was R&D for routine carry and functional reliability. It is tempting to experiment with however.

I have all three sizes. I switch them out. I don’t track one flu from another other than to know that they have been used in different configurations.

One flu, as a compact, had issues through the first hundred rounds. I assumed it was an upper issue more than an flu issue. I could be wrong. After that it hasn’t bobbled nor have my others.

I have the most rounds through the compacts and SC’s.

When I owned and carried a P320C 9MM for about 8 months, yes I tested it pretty extensively after changing from a Compact to Subcompact grip but I didn't start over.

The gun had been reliable for 500rds so I swapped to a SC grip, then ran another 250 or so rounds through it with it. Allows you to test the gun as well as get comfortable with the different configuration.

Then again, I don't like swapping anything on a carry gun without testing it before relying on it. I'll swap to a secondary gun until I can confirm function 100% with the pistol / rifle that has been worked on.

Weird things happen when swapping stuff out. Might be fine, might not. Don't want to find out at the wrong time.

I freely swap my parts around BUT I also fire the carry configuration every time I go to the range.

I have recently been playing (testing?) a .45ACP FCU in my Compact grip with my 9mm Subcompact slide. 150 rounds through it, including 30 Hornady Critical Duty 135gr +P. No failures of any sort at this point.

In fact the only feeding or cycling issues I have had with any of the 7 P320s I have or have had (sold a couple of FCU) have been with my X-Five and soft range ammo the first time out. Affter a hundred rounds or so though, no more problems with it.

When I decided to put a SC grip module on my 320 Compact for the summer months, all I did was take it to the range and run a box or two though it. No need to start from scratch after the initial 320C "testing".

Any issues would likely present itself in dry-firing the gun. The main issue I've heard/seen with the 320 and various grip modules is the grip frame rubbing against the trigger bar. My Team gun's original grip had to be slightly modified ever so slightly because of this.