I have left my 9mm 2.0 in Condition One for months. Not going to the range due to ammo shortage. Does it harm the pistol, mag, rounds etc to stay in One indefinitely? Thanks!

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It may get jealous of your other hobbies and run off with someone who will shoot it more.

I would say no, but like any gun with a self defense role (I'm assuming that because you said you left it loaded), it should be inspected, cleaned, and lubed periodically. I like to clean my self defense guns at least every 1-2 months if I don't shoot them for that long, and do a superficial cleaning to wipe off any dust accumulations as well as check to see if it needs lube every couple of weeks or so.

Also, dry fire practice is a good way to maintain skills if you can't get to the range. It's also a good way to do a basic function check to make sure everything's still working the way it's supposed to.

Just my opinion.

I agree with others. No, it won't harm any part of the firearm or ammo...
but...
It's a good practice to do the dry fire with the firearm, so additionally to your training, you also keep your firearm in working condition.

Please remember - shooting is a perishable skill...

NO, it doesn’t hurt anything. ContinentalOp does like many others and what I have done for many, many years (inspect, function test, clean and lube periodically). I do mine every 3 months if not carried and monthly if carried (sometimes more frequently if carried in hot, humid or cold weather).
I also try to have 4 mags for each gun that I carry concealed and rotate 2 mags every 6 months (No particular reason other than it makes me feel better to do it) and I always carry a spare mag.

Be SAFE and Shoot Often !

As long as you have absolute security of the loaded gun, I can’t see the harm. In my own case, I don’t like to leave auto pistols lying around fully loaded - just as a matter of principle, but I think you’re asking about mechanics, not principles. My young people are both old enough and knowledgeable enough to leave a loaded gun anywhere in my home or vehicles, but I still don’t do it. I hope I haven’t been too much of a bore with my mini-sermon.

An unloaded gun is not very useful IMHO.

Leaving the pistol loaded is not going to hurt anything, but as others have said, a routine cleaning to prevent corrosion is a good idea, maybe do that once a month, more often if in an area of high humidity or salt water environment.

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VCDL, GOA, NRA

The only thing I can add is... With striker fired guns that are loaded and chambered (especially ones without a manual safety), I like to keep them in a holster. Just a reminder that it is loaded and chambered when I pick it up.

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Centennial Every Day

The two pistols in the lockbox under our bed, the one in my shop tool box, and the one in the locked drawer of my desk all sit for many months fully loaded including a round in the chamber. No problems.

Condition 1?
Your M&P has a thumb safety, then?
Cooper Conditions only apply to pistols with manual safeties like 1911.

If your's doesn't (like mine) then there is no Cooper Condition, it is loaded or it is not.

Jeff Cooper didn’t “invent” the condition designations for the 1911, but the system can be applied to modern striker-fired pistols that are fully loaded and have no manual safety. That would be condition zero (basically). The gun WILL fire with no user-action other than pulling the trigger.

Cooper might have “invented” the idea of actually carrying the 92F in Condition Zero. He had some interesting ideas that many rejected out of hand, without even thinking about them. I, for one, miss him.

I carry my S&W M&P9 M2.0 5" with a round chamber all of the time. I go to the range at least twice a month. Dry firing several times a week. After 3.5 years, everything is working fine.

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O L James III
CPT Army Ret FA

Carried fully loaded, one in the chamber from adoption/issue in early 2006 until retirement in late 2015. No issues. However, our armorers did the 5 year/5K rounds mag and recoil spring replacement as scheduled.