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I’m sure this question has been asked lots of times before, so please indulge me. Is it true that you can’t convert a P320 9mm, .40,357 to a .45 ACP?
 

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From what I understand, yes, that is true. Based on the posts I've seen, this tends to be a hot button among P320 45 owners, since SIG at some point promised compatibility.
 

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This seems to be unique to the P320, it's not an issue with the P250. My four P250 FCUs were born from the factory as P250C-22-BAS (.22 LR). They're 100% X-Changeable.

This brings about the question, do have you have to make sure the mag safety tab on a P320 80%er is .45 ACP mag compatible?
 

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It can be done, but doing so would

1-void your warranty
2-potentially make your FCU into a paperweight if not done carefully.

I built my 80% to accept all calibers...

First you would need to trim down the ejector to somewhere between .470 and .495. Doesn’t seem to be too critical...
Second, you would need to trim down the takedown safety lever (note the difference circled in blue) I recommend buying a second one as doing so would defeat its purpose when converted as 9mm as the .45 takedown safety lever does not require the 9mm magazine to be removed when rotated....hope that makes sense....

I don’t recommend trying this on a factory Sig FCU. It is best done on an 80%....
 

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I call b***! I took nfcu for a P320 design for 40 caliber, 357, and 9 mm. Sick told me it could not be done, like I said I call b***. I modified the takedown lever, I modified the extractor and got a different hand module along with a 45 ACP magazine. 500 rounds later oh, I am a happy dude!
 

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I already did a build that way. You didn't mention the upper. Just in case some one was planning to do same thing I just bought it up. Although I wondered if there is a way to fit .45 cal barrel to a 9mm upper. It probably could be done with machining the slide. I doubt it would be practical and strength of slide could be compromised.
 

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I already did a build that way. You didn't mention the upper. Just in case some one was planning to do same thing I just bought it up. Although I wondered if there is a way to fit .45 cal barrel to a 9mm upper. It probably could be done with machining the slide. I doubt it would be practical and strength of slide could be compromised.
Machining the slide would be impractical as ypu would need to machine the breech face larger, along with the breech where the barrel locks up as well as the muzzle end of the slide. The slightest mistake would ruin the slide. Even when done it is likely to not work properly as the extractor was positioned for 9mm....

Just buy a 45 slide.
 
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