"I have a full size Witness 10mm. My question is, will the full size 40 cal mags work in this gun? How about the CZ mags? Any info will be helpful, thanks!"
I'm not sure from your post but it sounds like you may not be aware of the difference between the two frame sizes vs the two frame styles. If I'm out of line here then just smack me. But it looked like a good spot for a quick refresher clinic now that this post has grown so much. Greybeards of the clone board please correct me where I'm wrong, but keep in mind I am making this general, I'll point out some exceptions at the end.
There are two basic styles, usually called full-size and compact. There are also polymer and all-steel versions of both. For mags this isn't a big concern so we won't go into the polymers here.
There are also two frame sizes, usually referred to as large frame and small frame.
The small frame shoots (basically) 9mm and 40 S&W only. It is available in both styles, full-size and compact.
The large frame shoots (basically) 38 super, 10mm and 45. It is available in both styles, full-size and compact. They can also be converted to other calibers, including the ones used by the small frame version. This will muddy the water some as we'll see later.
Magazines intended for the large frame will not interchange with those intended for the small frame. Period.
Magazines for the compact will not fit a full size frame style(obviously because they are too short). However magazines for the full size frames will fit the compact style, just stick out a little on the bottom. More on that later.
Now, within the lineups, there is another thing to remember; the caliber of the magazine. For all intents and purposes, there are three basic "calibers" of magazines, and they roughly correspond to the boltface on the slide, which is geared to the diameter of the bullet rim. For the small frame there are two, 9mm and 40. On the large frame there are three, 38 super, 10mm and 45. The magazine has to match the shell diameter to feed properly. No matter what the magazine is marked, it is one of three basic sizes, 9mm/38, 10mm/40, and 45.
Now, to put all this together and answer your question about 40 mags in a 10mm, we'll walk through the basic questions you have to be able to answer to order the correct ones.
1) Is your gun style the compact or the full size? If it is the full size you can't use the compact mags, if it is the compact then you have to decide if you want a larger magazine that protrudes from the bottom or not.
2) Is your gun the small frame or the large frame? This is important and i can't stress this enough, it goes right over some people's heads. CURRENT CALIBER DOES NOT NECESSARILY MATTER, ONLY THE FRAME SIZE!!!. So many people ask things like "Will a 40 mag work in a 10mm?" and get ticked off when the answer is "maybe, it depends". I don't have my calipers or my pistols handy to give measurements but one way you might tell is if you know what caliber it came in from EAA. If it shoots 38 super, 45 or 10mm you have the large frame. The reverse is not always true though. If it shoots 9mm or 40 S&W, it is likely a small frame, BUT it could be a large frame set up to shoot one of these calibers.
3) You've determined the length of the magazine you want (compact or full size) and the frame size (large or small) but you aren't sure what caliber. This gets to be more important in large frame conversions to other calibers. 9mm and 38super have the same shell diameter, so yes, one should feed the other. 40 and 10mm, 357 sig share the same shell size. 45 is all by its lonesome unless you really get into the wildcats like 9x25. If you get this far, you shouldn't be looking at this post for answers though
Polymer notes: I don't have experience with the witness P, but I think all the rules above apply. The unique thing about the polymer full size large frame mags is that they have a little rubber spacer doodad on them that makes them fit really well in the compact model. I don't know if there is one for the full size small frame magazines. I assume so.
Non-witness mag notes: That is the other half of the story and a lot of what this sticky was originally about. This post is just for the witness alone.
41AE notes: This is an oddball caliber. It uses the boltface and slide of the 9mm, but it has its own magazine. The only ones I've seen are for the small frame model, and they are of an older style baseplate. They will fit in the full size and the compact, but they aren't real comfortable to hold in the compact. The reason these were popular is that they were available at one time cheap, were high capacity and they seemed to cycle reasonably well with 40S&W, which is almost the same size. Back when hi-cap 40 mags were scarce, these were a cheap easy way to fit your 40 cal witness with a hi-cap mag legally. In reality though, if you have one it is worth more as a collectible than anything, they don't work well enough and totally suck in the compact for anything outside the range. If you also have a 41AE barrel then keep both as an accessory or see if you can find a buyer. I personally wouldn't mind scoring another barrel, and I bet there are those who wouldn't mind having the mag.
Newer frame note: I'm still not sure I gather what EAA is doing but I believe all their imports are now on the large frame. I have been out of commission for awhile so I am just catching up. The above should still apply because there are still plenty of the small frames out there NIB on jobber's shelves judging from the last gun show I went to.
