As Roberts has frequently said, the M&P series excels with both the 9mm and .40, so which you choose will depend on your needs. If you are looking wanting a caliber that is more barrier blind, such as shooting through windshields/doors/barricades, then the .40 is a better load. Since the M&P is optimized around the .40, the only real disadvantage you can put your finger on to the caliber is the price of training ammunition. Now days, you can get cheap brassed cased 9mm for around $.20 a shot if you buy in 1000rd cases. The .40 is around $.30 a shot by the case, and the .45acp is around $.34 a shot by the case. So what you go with depends on your budget, how much ammo you go through in training, and if you are concerned with shooting through barriers.
Oh great, a caliber debate. Do some poking around on here, especially the terminal ballistics section, and make an informed decision on caliber. Looking at your targets I’d say buy a 9mm, a bunch of ammo, and some competent training. Focus on learning how to group first.
Conversion barrels don’t run well in my experience, though I’ve only used them with Glocks and drop in fit barrels. A smith fit barrel might be a different story but for the price you’re almost better off just getting another gun. I did the conversion barrel thing with Glocks a few years ago before I realized that I had no reason to own or shoot .40 S&W. I got rid of all my .40s and now just shoot 9mm and am very satisfied with that decision. I look at 9mm as a perfect self defense round in terms of effectiveness, shootability, and cost. In my eyes .40 S&W is a cop round for shooting through windshields and whatnot. For a private citizen I don’t think it’s worth the hassle.
I’d choose 9mm. I don’t generally like .40 polymer guns personally. Todays ammo, terminal ballistics difference is minimal*, less recoil/faster follow up shots with 9mm, more $$$ for ammo and training (unless your job supplies it), higher cap, etc.
IDPA: if you are competing in IDPA to simply enjoy and work on your own shooting, shoot what you will carry and be happy. If competing to compete against other shooters, you will be in SSP. That means you will compete against shooters shooting 9mm guns, and high level competitors in IDPA in SSP (almost) universally shoot 9mm, because of the reduced recoil, faster follow up shots.
If I was going to get a M&P in a larger caliber then 9mm, I go .45 ACP at that point, but that’s me. 
- however, see docs comments on issues of intermediate barriers, etc
My thoughts exactly.
Go with 9mm simply for the savings, you won’t be shorted on terminal performance. These days with the right loads you are splitting hairs between 9mm/.40/.45.
And you will be eaten for lunch by those shooting 9mm in IDPA (the comp he mentioned specifically). He will be in Standard Service Pistol (SSP) with that M&P. There are steel targets in IDPA, but vast majority of the time, it’s IDPA targets. Yes, steel needs a better placed shot with 9mm, but it’s not offset by the other 90% of the time the time lost with IDPA targets shooting a polymer .40.
If the shooter is there to simply enjoy competing against themselves and improve their own shooting skills, shoot what you carry and drive on.
If looking to be competitive against other shooters in your ranking and division, you’ll find 9mm tends to rule.
I shot CDP for a long time as it’s .45 ACP 1911, and I enjoyed that too.
Accuracy, and accuracy under time, are two very different issues. If I put a timer on you, and make you push your time, you will either take longer to stay as accurate, or your accuracy will suffer, compared to 9mm.
To truly be as accurate with a .40 (all things being equal) vs 9mm, takes a lot of range time and ammo, and I personally only know a few people that are truly able to do it. Now, one can of course debate the slight increase in time lost is offset by the slightly larger hole made and so forth, and that’s all valid discussion, but shear accuracy comparisons without time factor added, is not (in my view…) useful info if discussing SD issues with different calibers and so forth.
No. No more POA/POI shift than changing load in the same caliber (40 S&W 155 gr to 180 gr) Most of my handgun shooting is 25 yds and in. Sometimes we set USPSA, IDPA or steel targets out to 60 yds, but very seldom. No issues.
Glad I don’t shoot at your matches! 
Not matches, 5 to 10 of us get together every Friday and practice. Every once in a while someone will set up a long shot or two in order to force the shooter to slow down…
Our matches follow USPSA and IDPA rules, obviously depending on the discipline hosting the match.
Well that makes more sense. Don’t think I have ever seen a target past 25 yards at an IDPA match, but I could be wrong there.
What is this slow down of which you speak?
From the IDPA rule book:
Course of Fire 2. Seventy-five percent of all shots required in a match
must be fifteen (15) yards or less. Occasional targets out to
thirty-five (35) yards are to be encouraged.
Most IDPA matches I have shot stick with the 15 yards or less.
This wasn’t meant as a “caliber debate”, it was meant as a conversation. You know like you would have sitting at the bar after an afternoon of shooting with a bunch of guys just spitballing about a future weapons purchase. Since most of my friends and family don’t know jack shit about guns I came here.
+1
When the OP asks if he should go 9mm or .40, then there will be some element of a caliber debate going on.
Which is not the worst thing in the world if we don’t devolve into shit-flinging rednecks hollerin’ about STOPPIN POWER and how THEY ALL FALL TO HARDBALL…
In that case, it must be 10mm!
Never seen a target yet at 35 yards* at IDPA in this area, but ranges around here rarely have distances like that for handgun that would fit into their range size/design, etc, so probably as much a factor as any you just don’t see that in my area. On rare occasion, a 25 yard target.
It would be fun to shoot IDPA in states with much more open space and friendlier gun laws, like AZ (assuming by your name that’s where you are) and the ilk.
*= which does not mean they don’t exist around here, but not at any matches I have attended to date.
Will,
Touche on that man and better advice than what i gave out.For some reason I missed the IDPA part. My apologies on that one!
-Jax
None required, just adding the 411 where my limited brain power allows. :jester:
I shoot USPSA Production and a ton more Multigun. I use the M&P Pro 5inch 9mm for both. I’m running a Bladetech holster for both, but just put a Raven holster on order, which will be my new holster.
My carry gun is the standard M&P 9mm and I run it in either. Crossbreed IWB or a Raven LCH.