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Discussion Starter · #1 ·
Hey folks. I just bought a Glock 31 .357 caliber for a carbine MCK conversion kit. I’m wanting to have an extended magazine. I’m having a difficult time confirming whether or not I can just buy a 40 caliber extended magazine. One of my armorers at work says it should be fine. Just wondering…..thanks for your help.
 

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I'm pretty sure a .357 and a .40 are not interchangeable.

The .357 Sig and .40 are more inclined to work together, I believe the followers are different, for each caliber.

For fun it would be worth trying, for personal protection, I would use the appropriate mag for the caliber.
 

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Discussion Starter · #3 ·
I'm pretty sure a .357 and a .40 are not interchangeable.

The .357 Sig and .40 are more inclined to work together, I believe the followers are different, for each caliber.

For fun it would be worth trying, for personal protection, I would use the appropriate mag for the caliber.


Thanks. My problem is I can’t seem to find an extended mag for the .357 of more than 15 rounds. With this carbine setup I’d like to have a little more. Appreciate your response.
 

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A .40S&W mag should work but I would swap the follower for a .357sig follower.

What I don’t know is the space between the mag lips - I think they are the same but I don’t have a 357sig anymore to measure.


Sent from my iPhone using Tapatalk
 

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I have both but no time to mike them right now.

Is not the .357Sig case just a bottle necked .40 cal case ?

I did read that the .357sig have a tendency to nose dive when feeding, that is why the follower should be changed out, although one point is that once the first round is fed, the remaining ones ride on the case of the one below it, until the last one.
 
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