Unfortunately, this is seemingly a rather contentious subject ...
The locking arm is held in its downward position by the tension exerted on it by the torque lock spring.
When the lock is engaged by the user a tab rotates and lifts the locking arm upwards against the tension of the spring, holding it in position for the arm's post to prevent movement of the hammer.
The torque lock spring is anchored in the bottom of the locking arm and the bottom leg of the spring slips over and down under a recessed shelf in the frame. The left side of the bolt seems to help keep the spring leg in place.
If the revolver is detail-stripped and the bolt removed, tipping the revolver onto its right side can easily cause the locking arm and its torque lock spring to fall free of the gun. This is one of several good reasons why a detailed disassembly shouldn't be done by someone who isn't trained and familiar with properly working on the guns.
When I've spoken to various customer service reps, technicians and the armorer instructor about the reason for some of the instances of reported failures of the ILS I've been given some different answers over the last few years.
It seems that not very many revolvers which have been returned for 'lock problems/failures' have actually turned out to have involved a 'failure' of the lock. Some number of them involved repairs to other parts. Some seemed as though they might have been related to improper installation of the ILS during initial production (although the way it was said it seemed to have have been a limited number of instances). I was told that in at least a few instances it was wondered if some potential owner-related actions may have been involved (as anyone who browses forums like this is aware, there are seemingly some curious folks who can't seem to resist getting inside their firearms).
I was told that a few early issues had been encountered and addressed with the ILS early during production, and the X-frame guns were mentioned at least once.
In my armorer class the ILS didn't seem to be a favorite design with the revolver enthusiasts in the class, although interestingly enough, nobody who had been using the ILS-equipped guns had any problems to report. One fellow claimed to have fired hundreds of Magnum rounds through his 360PD (
) without a single problem and he said his next purchase was going to be a M&P 340, through which he said he planned to exclusively use Magnum loads. More power to him on the exclusive diet of Magnum ammunition in one of those lightweight J-frames.
I prefer to use +P loads in mine. The point is that he had no problems to report when shooting Magnum loads through his Airlite Magnum J-frame.
The armorer instructor, when asked specifically about the ILS and any student reports of problems, told me that he hadn't received any reports about ILS failures among his LE armorer class students, nor had he heard of any. It just wasn't a hot topic among LE users of the popular little J-frames. While removal and replacement of the locking arm and spring was briefly discussed during the class, it wasn't a 'hot topic'. (BTW, we were told that removal of the remaining 3 parts of the ILS from the frame - the lock tab, fork and coil spring - was not recommended under normal conditions because of how it was press fit into the frame during production.)
FWIW, I've handled and used several of these little ILS-equipped J-frames, and know several other folks who own them for use as secondary (back up) and off-duty weapons. One of my J-frames has the ILS.
Neither myself nor anyone I personally know have experienced any issues related to the ILS unintentionally engaging. Some of the other typical revolver issues have arisen from time to time, but nothing with the ILS itself.
When I've ordered some spare parts at different times I have noticed that the torque lock spring has been listed as a revised part. Nobody has been able to tell me what that means. Lots of parts are constantly being revised on S&W pistols, though (as with a number of other firearm manufacturers).
Now, while I also wish S&W would change their ILS to one which wasn't as visible (cosmetic issue for many folks) and functioned in a different manner (using only spring tension to resist undesired movement of part of the locking mechanism under recoil), it doesn't seem to be a huge problem from what I've heard and experienced.
Other folks certainly seem to have their own opinions on this matter.
Yes, I've also heard an unsubstantiated rumor to the effect that S&W may be considering adopting a different lock design. Nobody I've personally asked about this claims to have any inside information, however, and the source is at best second-hand. Maybe. Maybe not. Time will tell.
I think the limited production runs made from some older pre-ILS J-frame parts inventory has spawned a number of rumors, too.
Just my thoughts.
