The intent of my statement was, I thought clear. I did reverse the caliber swap in my original post, but that was not intentional. I have corrected my original post.

What is amazing to me is that the reader who wanted to criticize MP1SG could not discern (1) that it was my quote and not that of MP1SG and (2) that I meant to say .40 to 9mm, since going from 9mm to .40 is clearly not an option as the breech face is too small

It should be OBVIOUS to all concerned that you CANNOT go from 9mm to .40 by changing the barrel and magazine as the larger case head of the .40 will not work in the 9mm breech face.

As I said in my original post, going from .40 to 9mm MAY work, but it is a bad idea as the larger dimensions of the breech face of the .40 do not properly hold the 9mm, and the extractor will not grip the 9mm case head properly. While this may work some of the time, or even most of the time, it is ABSOLUTELY not to be trusted for carry or self-defense. In addition, inevitable malfunctions will reduce confidence in the weapon as you will never quite be sure if it is JUST the wrong size ammo or if the extractor has been truly damaged by this practice, which will undoubtedly put stress on the extractor that was not intended by the designers.

I stand by what MP1SG says and by my original post (except for the mistaken 9mm to .40, which has now been corrected to .40 to 9mm.

These amateurish caliber conversions in pistols not intended for it are a BAD idea at best and perhaps dangerous at worst.

Since it is apparent by the number of questions and discussions that seem to repeatedly crop up on this topic, it seems that either folks have no idea how to use the search function, or they simply do not wish to hear the truth, looking instead for some kind of validation for their bad ideas.

If you want to shoot 9mm, what is wrong with just buying a 9mm?

Thank you MP1SG for lending some common sense to this thread.