I have a 10mm compact, but I'll guess that you have the same problem I had. First of all, my extractor also has absolutely no tension (something I need to fix) but I think that might not be your problem.
this goes for every 12rnd magazine I have. If I loaded the magazine to capacity and than strip every round by hand, every once in a while the follower would bind up and the cartridge would nose dive, hit the front wall of the magazine, and jam up. I imagine that the slide has enough brute force to jump the wall and send the nose straight up, causing a ftf.
It appears that Tanfoglio did not redesign the spring for a compact, but are cutting their full size springs to size. Since their springs are staggered and each coil is smaller than the last, cutting the spring from the bottom leaves a bottom coil that is to small to fit over the hump in the floor plate and properly seat.
I suggest that you take one magazine apart, and take a look. Also notice if the top coils in your spring are narrower than the bottom coils. If the coils are the same size, you probably have an aftermarket spring, and things just got more complicated.
First take the spring, and bend the tail of the bottom coil back up to be even with the wire on the other side. (That was my clue that full size springs are cut instead of a dedicated design)
Second, push the.bottom coil over the hump in the floor plate, and under the small ridges on the sides of that hump, it should be a tight fit, and the floor plate will be securely held. (An aftermarket spring will most likely not fit over that centering hump.)
Now, holding your thumbs under the floor plate with your fingers compress a few bottom coils onto the floor plate. If you have the same problem I had, the remaining coils are to small to slide over the hump, leaving 1/4inch space in the back, and tilting the spring forward.
I believe that this forced tilt binds the bottom half of the spring. The top half has enough compression to feed a few rounds, than the follower stops pushing, the next stripped round nose dives, the case catches the front wall of the magazine and the brute force of the slide catapults the nose straight up causing a jam. When you clear the jam, the vibration and extra room unbinds the spring, and the gun fires with no other issues.
Than again, I'm not a gunsmith, not even an experienced shooter, so all of this could be BS.
To fix the problem I guess I could get a full length spring and cut it from the top instead of the bottom, but one of my followers is black, and needs the small coils to fit properly. Not sure if wider coils would cause any problems with the red followers, I didn't try it.
I took a dremel with a sanding drum, starting light in the middle and going heavier towards the back of the hump (flat part of the floor plate) I sanded the hump down enough just so the first coil had something to grab on to, and I didn't damage the ridges on the sides of the hump that hold the spring down.
The remaining coils still don't go over the back of the hump, but there is very little of the hump left to cause any problems, and the spring tracks straight. I left the front of the hump alone since it didn't seem to cause any problems, and the coils slid all the way down.
5% wolf springs were a bit more complicated. The coils are small and same size all the way down. On one magazine I sanded most of the hump flat, just leaving the first 1/4 ( which also had to be sanded on the sides to match the width of the coil) for indexing of the spring.
So far none of my magazines are binding any longer. I am running one magazine with a black follower and stock spring, one magazine with 5% wolf spring and red follower, and 3 magazines with red followers and stock springs.
This worked for me. Your mileage might vary.
As I said before. I am not a gunsmith and have a very small sample to work with. And I'm not suggesting that you should modify the magazine in any way. My witness is a range toy. I shoot it, and I take the risk. I would not modify any defensive firearms my self.
I noticed that the witness is a bit sloppy, next on the list is tuning the extractor tension, and a Henning guide rod. Once that is complete, I can respring it, and finally tune the ejector.
Edit: got the new extractor in mail today and it also did not put any tension on the cartridge. The extractor stop was at 0.052, I filed it down to 0.043 before it applied any tension in my pistol. Extractor was marked .40
I'm curious if all LF witnesses in .40/10mm have such loose extractors
