Well, I found a suitable replacement spring for my extractor. I ended up getting a "rear pin detent spring" off of an AR-15. These springs have a similar diameter, but are stiffer and longer. I simply cut a chunk off that I felt was the right length and then stretched it out a bit and sanded the ends down flat. It's seems to be working perfectly fine for now. You can find these springs almost anywhere. I got mine at a local gun shop for $1, and it's long enough to make 3, or even 4 Chiappa extractor springs out of it. Now back to the extended mag...
The mag seems to work fairly well. I can put in a total of 20 rounds at the moment using two of the stock 10 round springs. You can not however insert the mag while the bolt is closed (there isn't enough spring compression space left after 20 rounds in there). So for now, insert the mag with the bolt open. Second thing, I had a few times where the first couple rounds would nose dive into the base of the breech and cause a jam (the nose wasn't properly aligning with the chamber). I was actually able to remedy this by tightening the mag well set screw in a little bit. Which is weird, I figured I would have to loosen the screw to make the mag fit more snug, but all that did was cause more jams. The mag ran 99% more reliably when I tightened the screw in and ran the mag sloppier. I noticed that the mags are coming out 200-400 microns too small on the body dimensions, (compared to my stock mag). So I'm going to re-size my model and do some testing before I release an updated file. Maybe you can just increase the overall size by .5%? I'm not sure how this would affect the mags performance and reliability though. But overall for an "EXPERIMENTAL" extended mag, I'd say it's working pretty darn good! I'll update again when I get new springs, and redesign the mag slightly for a higher capacity, and possibly better feeding reliability.
I split the model into two pieces so it can be printed more easily on printers with lower z axis ceilings. I was able to squeeze 19 rounds tightly into this mag by using two of the 10 round mag springs butted up against each other. (spring to spring, nothing in between)
It's seems apparent that after doing this that two springs may be just to long for this mag, and a shorter spring would allow another 1-3 rounds. Looks like the mag will hold 23 rounds with some modifications made to the follower, springs, and the spring plug. I was gonna test this mag out for reliability, but I was having extraction issues when dry cycling the rounds. Then I noticed my extractor spring had wiggled its way out and was long gone! That spring is so tiny, I doubt that I'll ever find it. So I can't do any testing until I get a suitable replacement. I made a few changes to the lip I complained about earlier in the middle of the mag, but after I printed mine, everything seemed perfect. No lip, and no problems. I went with 4 shells (a little over-kill) and 3 base and top layers with a 45% honeycomb infill printed in PLA at .100 microns. After doing this I would suggest upping the base and top layer to maybe 5+. Or simply increase your infill %. Once again, I just used the guts from the 10 round mag I have uploaded on thingiverse found here: https://www.thingiverse.com/thing:2403229 and you'll have to use supports for under the 3rd lug. I'll update as soon as I get the extractor fixed.
"EXPERIMENTAL" extended magazine for the Chiappa M1-22. I modeled the magazine after the Seymour type III mags. (excluding the holes on the body) I don't really know what the holes were for on the carbine mags. I'm guessing drainage for water and mud. But I left them out of the design for now. Also included is the 3rd lug on the side. Seeing how the M1-22 has the extended arm on the mag release for the 3rd lug, it only seemed right to add it. I have no idea what orientation to print this in. My printer (Flashforge Dreamer) isn't tall enough. So I might have to try printing it on it's back with supports. For the internals, please try using the parts for the 10 round mag I already uploaded. For the spring, you may be able to "double up" two 10 round springs and add a connector in the middle to keep them together. I have no idea how the other parts will interact with this body, and I have no idea how many rounds this thing will truly hold. I'm hoping between 20 and 25. This is why I call it "EXPERIMENTAL". Please comment on your experiences with this mag, I would love to perfect it over time.
NOTE I noticed that where I extended the 10 round mag to make this one, there is a small .08mm lip that "may" cause problems with the follower. This is because the bottom portion of the mag has a different curve in the follower groove than the top does. This had to be done to keep the dimensional accuracy of the M1 Seymour mag. If anyone has a problem with this lip, let me know so I can address it.
your choice, but .100 is probably best
I haven't tried printing it yet, so I have nothing to report here at this time.