I have several of the Glock 40SW LEO turn ins (GT Distributors, AIM Surplus, etc). They perform fine with 9MM conversion barrels and magazines.
I was thinking about picking up a SW M&P LEO trade in and of course a 9MM barrel will be one of the first accessories bought.
In the Forum’s experience, how do the M&Ps handle the conversion barrels?
I am assuming these are M&P 1.0 pistols, NOT the 2.0 version.

A few thoughts-

These guns will do fine converted to fire 9mm. For range/plinking, you can get away with just dropping a 9mm barrel in and rolling on. I'll be reliable and accurate enough.

Me myself personally.........I would not drop a barrel in and try to carry it or use it for anything my life depends on. And I say that knowing full well that most likely it will function without any issues.

If I were going to convert ANY .40 caliber pistol to 9mm for carry, I would have a proper conversion barrel fit by a gunsmith.

With all that being said, as cheap as M&Ps are right now, why bother. I'd watch places like Palmetto and just catch a 2.0 on sale.

Hope this helps.

Not as a carry gun, just to dip my toe into that series of pistols.
I don’t carry my converted GLOCKs either.
I understand the differences involved in measurements regarding breech faces, extractors, ejectors, etc.

I tried the switch with a factory 9mm barrel in my M&P40c 1.0. It works very well for play and range, but failed to extract (to be expected) just enough (about 1 in every 100) that there's no way I'd trust it for serious work.

Later, after I'd done quite a bit of research, I bought an Apex conversion barrel for my 5" M&P PC 1.0. I had a gunsmith fit it and that thing flat works. As of now, I've put a few hundred rounds of HST and about a thousand of pot luck FMJ's without any trouble. It shoots a such tight groups that I'm using it in a local bullseye competition.

Still, like Jerry said above, it might not be worth all the trouble when M&P 2.0's are going so cheap nowadays.

I got a Storm Lake 9mm convo barrel for my 40FS about five years ago, and have about a thousand rounds thru it so far with zero issues.

Just today I put my Storm Lake conversion barrel in my old 357M&P and went through 5 mags fairly quickly. I had about 8 FTEs... This surprised me because when I first got that barrel, it worked quite reliably [IIRC].

I'll give the extractor hook area thorough cleaning and try to figure out if something else is up.

Now that I'm retired and no longer have a connection for cheap 40S&W ammo I'm planning to shoot a lot more 9mm...good thing I just scored a 9mm X-Change kit for my 40 cal P226...

I'm using Storm Lake 40-9 conversion barrel. No issues with mine.

You can get your hands on brand new M&P 2.0 pistols for sub $400. With conversion barrels running around $150, it's hard to see the value in buying a used one and barrel. Especially since the 2.0 is truly a better gun than the 1.0 that makes up almost all of the used M&P market.

Y’all convinced me. I’ll probably just wait on a 2.0 M&P.
In the mean time I can save up for all the ancillary costs...holsters, mag pouches, etc.