I own a pair of M&P 340's. The first one came off the first production run (I was told by someone at the factory, when I ordered it). The second one was when they started producing them without the ILS (lock). I thought it would be interesting to own one of each version.
Both have been used for a fair amount of range work, but the first one became my regular 'range beater' J-frame, allowing me to spare my pair of 642-1's for most of the range work. It's seen a lot of off-duty, and now retirement, carry. It also became my 'practice' revolver after my revolver armorer class. It's acquired some nicks, scratches, dings and rub marks (although not nearly to the extent of the one Mas carries
).
While I ran some boxes of .357MAG through the first one to become acclimated to it, I found I much prefer using +P loads, so that's what I use for the bulk of my range work (quals & drills) and carry. I'll often finish a range session with a cylinder load or two of Magnum loads, just to assess controllability after tiring a bit over the course of a range session.
I didn't buy either of the M&P 340's because they were chambered in .357MAG, but because they were produced with a Scandium-alloyed aluminum frame, had a PVD blackened stainless cylinder and a XS front night sight. I'd have bought them even if they'd only been chambered in .38SPL (and rated for +P). The nicely visible front NS and the rear sight channel are practical and useful, for someone who understands the 'big dot' sighting system (I've owned a set of the old Ashley Big Dot sights on a CS45 for many years).
I ended up replacing the original Bantam grips on both of my M&P 340's with older UM Boot Grips, which actually adds close to an ounce of weight.
Although both of my 340's have benefited from armorer-level inspections and deburring, the first one (with the ILS) has a very smooth and nice trigger, after all of the range use it's seen. I've even replaced the extractor a couple of times, just to practice using the extractor-cutting tool to fit a couple new ones (part of the revolver armorer tool kit). While it didn't need it, I also replaced the ILS locking arm and torque lock spring, just for practice, since we only did it once in the class. It's seen quite a number of cases of rounds fired through it since '05, and some initial dry-fire, all of which contributes to a very smooth trigger action.
I like to think of the M&P 340's as 'improved' 642's. Better sights, black finish and a slightly stronger frame.
Not fun to use to shoot Magnum loads, and even +P loads can eventually cause the trigger guard to whip upward and hammer the bottom edge of your index finger's distal knuckle enough times to make it tender.
