I've occasionally experienced, and have seen (revolvers of other's), S&W revolvers seize during live fire ... but none of them have involved the ILS (lock). Various other mechanical problems were involved.
One of them was really interesting, and a problem I'd never seen or even heard of before, in a NIB M617. The owner brought to us at the range (since a couple of range staff were S&W revolver armorers). The trigger and hammer were sluggish and difficult to function using the trigger, and it finally completely seized while I was checking )not shooting) it.
When I opened the side plate, I was kinda amazed to see that the spring for the hammer sear had come out of its spot, and had somehow dropped down low enough to have become entangled in the area of the hammer, trigger and rebound slide. It had become "cut" apart when it was caught up in the movement of those parts. How weird is that, right? (The repair was a new hammer sear spring for the MIM hammer.)
During my revolver armorer class I had a chance to ask other armorers in the class, from a number of agencies, about any "lock" failures they experienced or reported (confirmed). The answer was none. The guy teaching the class told me that he'd not yet had anyone in a revolver class report experiencing a ILS failure, either.
Looking at the way the itty bitty torque lock spring (installed on the locking arm) is supposed to be positioned and installed in the recess within the channel of the bolt (pretty much held in place by the presence of the bolt), it looked pretty secure.
However, then we saw that if someone opened the gun and removed the hammer and bolt, and then tipped the gun onto its (right) side, the weight of the locking arm could easily cause the spring to drop out, or just slip out, of the then-exposed recess. If the spring leg was no longer anchored within its intended recess, it couldn't hold the locking arm down.
This started to make some sense when it came to an occasional internet report of how a new model S&W revolver (with the ILS) might've experienced a lock failure after it had been opened up and worked on. Obviously, it also made me wonder if a moment's inattention during production assembly might've resulted in someone not properly installing the little dog leg of that torque lock spring.
Many years ago I used to have conversations with different folks at the factory, when calling and asking questions as an armorer for their various models. At various times I heard (from different guys) how a few very early problems with the ILS had been caught early on. One of the guys said those were identified early during the X-frame development (due to the significant recoil forces).
A revolver tech told me that he'd received a few warranty returns from owners claiming lock problems, but none of the guns involved had actually experienced lock problems. Instead, they involved other fitting issues that required repair, like DA sear stubbing and fit. (In the revolver class we were told that 90% of the hammer DA sears were dropping in new guns and working without any fitting, but the other 10% still required fitting.)
I know when I got my only J-frame that had a ILS (first production run of the then-new M&P 340), I looked at it with a bit of a suspicious eye. I checked the parts list and saw that a revision of the torque lock spring was listed, but didn't know which it had happened. Afterward, when I came back from my armorer class and was anxious to practice my new revolver armorer skills, I ordered a few extra torque lock springs and locking arms for the J's. (The springs had to be installed in the locking arms for installation, and they're small, as is the little slot in the locking arm, and there's a nub in the recess, past which one end of the spring's legs has to be forced. Let's just say young eyes, or a magnifying lens lamp, are handy.)
Even though my year old M&P 340 hadn't exhibited any issues with the ILS (lock) with all of the Magnum, +P and normal .38 loads I'd been using (a lot), I assembled and installed that new locking arm & spring for practice.
Many years later, and a respectable number of cases of various ammo later, I still haven't had any issue with the lock.
I've seen quite a few new style J's come through our range since the ILS was integrated in the guns, and none of them have caused issues for the owners, either, and most of those have been in the hands of cops using them for of-duty weapons. I've seen some CCW licensess's use them for range quals over the years, too, and no problems from them, either.
I've asked S&W's LE sales management folks about sales of J's to LE agencies and cops. I think it was NM State Police who buying and issuing new model M637's as secondary and off-duty weapons. I was told nobody was aware of any reported complaints from LE agencies at that time (mid 2000's).
Now, only one of my several J's have the ILS, and I'll acknowledge I tend to prefer the aesthetics of the smooth frame side versus that of the hole for the ILS.
I even ordered one of the newer model M&P 340's that was finally offered without the ILS, just to have one of each (any excuse to own a pair of them
).
That said, guess which M&P 340 it is I mostly carry and prefer to shoot? It's the one with the LOCK. Why? Well, it's never failed me in 13 years ... and I did a fair amount of shooting with it when the ammo was stocked in our range inventory. It's acquired a fair number of scratches, nicks and an unexplained dent (in the trigger guard, of which I have no memory of how it got there). It's been my normal "range beater" and my frequent daily off-duty and retirement carry weapon for some years. During that time & use, its acquired a pretty smooth trigger pull, too.
From what I've heard now and again, as long as the revolver has an exposed hammer that can be cocked into single action, the corporate legal folks at the company aren't going to recommend ditching the lock.
Just my thoughts. Everyone's got 'em.
