How much difference in size is there between a
3913 and a CS9 I have a 3913 and would like to get
a CS9 to EDC also.

IIRC about a 1/2 inch on both grip and slide......

but the CS9 has a "finger rest" on it's 7round mag..... which makes it as tall as a 3913 if you can find a flush fit 7 round mag. (yes they do exist) vs the more common 8rd magazine that also extend below the 3913 grip frame. (note the flat base 8rd mag is shorter then the one with the finger rest..... about 1/4 vs 1/2 inch)

I have several 7rd flush fit magazines and carry IWB so I found 0 sum gain in getting a CS9 ...... so I passed when they first came out.

As some around here say YMMV...."Your mileage may vary"

The flat base from the 8 round 3913 mags will fit the CS9 magazines. When I had a CS9, I found that the finger rest would hook my shirt and risk exposing my gun. Which is one reason I went to a pre rail 3913TSW.

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Can open, worms everywhere.

What would be the smallest gen3

The CS9....... remember the slide/barrel is 1/2 inch shorter than the 39xx guns......and per GaryS you can shorten the butt a bit with the flat mag base....... FWIW the 7rd steel base flush fit 39xx magazines are scarce and will be hard to find.

I own and carry examples of both. And the CS9 fills the niche of a deep concealment carry or BUG. Fills it very well too.

They both have their place and compliment each other. Get one of both models. You will be glad you did. Regards 18DAI

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7 +1 Rounds of hope & change

The CS9 (and CS45) are excellent guns IMHO.

I found the grip on the CS9 just a little too short to comfortably get a 3 finger grip. My pinky was half on/half off using the finger extention magazine base. The 3913 is perfect for a 3 finger grip.
My CS9 was very accurate and I probably should have kept it, but went to 3913/14's for the better fit in my hand.
A Google image search of CS9 vs 3913 may turn up some side by side comparisons.

Can't go wrong with either. Yeah the 3913 feels a bit better in the hand but something about that CS-9 for the cargo shorts works for me.

I'll second this sentiment!
I have a couple of each and I love them all equally. The key is to keep buying these gems and never sell one. 😉

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Kirk / Spock 2020

I will be the voice of dissent. I found i did not care for the CS9 factory rubber grips at all. Like a fist full of play-dough. And aftermarket grips (big dog) were over $100. Calculate that into your cost. Fwiw: the 9 round 3906 mags with a kahr mk9 mag sleeve worked for a reload. But i still sold the CS9. If i need to go smaller than the 3913 i grab a j-frame.