I bought my P320 pretty early on and since then I've wanted a manual safety. (I'm not here to argue the merits please, but I'm a 1911 guy at heart, so there you go) Even though later versions were offered with this as a factory option, those FCG's are still tough to find in .45 ACP, and I really don't need another one or want the hassle of dealing with an FFL, and my local pistol licensing bureau, which would add more cost to already expensive FCU.
I came across AB Prototype, San Diego, CA, in another thread here, and figured I would give them a try. For 199.00 I could ship directly to them (with required documentation as they are an FFL) they would do the conversion using only Sig parts, and include shipping back to me directly, so no PITA FFL or fees. I am here to tell you guys, it's money well spent! Turn around time was about a week, from arrival at their location to return to me. It was explained to me that they usually do the FCU frame milling in batches, usually every other week, so I must have hit it just right, nice!
The fit and finish on the parts is excellent, and they perform flawlessly, as you would expect. The required milling on the grip module to accommodate the safety lever is also top notch. The grip I sent them is different than the one I tested the gun with as I'm still waiting on another vendor to finish my full sized slide milling for an optic. Modifying non-safety frames to accept a safety FCU is a piece of cake, and I did 2 grip modules in about 15 minutes.
Operation of the safety lever is firm in both directions, more so in the safety on operation (up), but both motions are firm, and tactile. It should be noted that with the safety on, the slide can be operated rearward, and a round chambered, which is nice.
I can't confirm that the factory FCU does this, as I don't have one, but I would imagine so. There was no vagueness or sloppiness in the operation of the controls, and the gun performed as it did before the conversion. I'm sorry I didn't scale my trigger pull prior to sending it out, but it doesn't feel any different to me.
If anyone is looking for the manual safety conversion, I would highly recommend the folks at AB Prototype. They do other gun smithing as well, so if I have a need that I can't handle myself, I wouldn't hesitate to contact Alex and the folks at AB.
Here are just a few pictures: