S&W Internal Lock - technical thread.


April 27, 2009, 06:12 PM
Please go to one of the many other threads if your interest is in complaining about S&W, legal ramifications, etc. We GET IT. Now, for those of us who have an IL S&W revolver...

Here are my questions (and I'm sure I'm not alone):

1. How exactly does the S&W internal lock engage itself?

2. Any thoughts about how to prevent any problems without removing it?

3. Would a dab or two of Loc-Tite or some sort of goop in the right places work to keep the lock from rotating without force applied using the key? What places?

4. What about removing the lock flag? How hard is that to do without boogering up the revolver?

5. Any other thoughts or information of a technical nature about keeping the lock from engaging at the wrong times?

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April 27, 2009, 07:22 PM
Good luck with keeping it on the straight and narrow.

Even I'll confuse the issue but I think it's in the vein you're looking for:
1. How exactly does the S&W internal lock engage itself?
Not really clear and what makes it less clear is that my sensei, one Old Fuff has essentially said that the "flagship" S&W lock failure pictured on Wiki is, in fact, bogus because hammers don't rebound as described.

Towards the end:
Partial Lock Failure The hammer rebounded from the recoil of a magnum load and the internal lock pin impinged enough to freeze it in place

The "rebounding hammer", however, was a substantial percentage of total claimed failures and I believe M. Bane's was similar if not identical.

I've heard (3 degrees of separation) of locked revolvers tieing up due to chrome flaking off other parts and getting wedged into the lock channel - this may not be a lock failure per se but it wouldn't have happened if the lock wasn't there so it could presumably be laid at the lock's doorstep.

2. Any thoughts about how to prevent any problems without removing it?
Yes. Grant Cunningham has given us a large clue-bat in his response to Tamara's "Lock mess monster" post.
Second, the problem is not the surface finish of the MIM parts - which are on the whole superior to a machined part. The problem is one of inertia: the flag, which is the part which actually locks the hammer, is shaped in such a way as to distribute its mass toward the greatest distance from its fulcrum. This translates to a moment of inertia which easily overwhelms the very weak return spring, allowing the flag to move into the locked position.

In addition, the return spring's fulcrum is very close to the pivot point of the flag, reducing its leverage advantage dramatically.

The number of time the lock has been engaged appears to play no part in the failures. The difficulty of engaging the locks when new comes not from the movement of the flag, but rather a) friction of the tumbler inside the frame hole and b) friction of the mating cam surfaces on the tumbler & flag.

I've done a bit of experimentation with reducing the mass of the flag in an attempt to reduce its moment of inertia, and initial results are promising. Of course, the option of disabling the flag's locking portion or of removing it altogether may be more appealing to many people.
Bold mine. So far as I know, nobody else is experimenting along the lines described by Mr. Cunningham. His notes are from May of '08 so it's not exactly "hot off the presses".

3.: I think so. But...

4.: Sounds like what Cunningham has experimented with. And

5.: I like Grant C's line of research - if it works it would probably be something gunsmiths would do without getting a case of clenched sphincter as the the thing is left intact albeit with reduced mass in some areas.

Note also Grant's remark about "overwhelms the very weak return spring...". There is unsubstantiated internet back chatter which holds that S&W has "slip streamed" a heavier spring into the product. I'm one of the conspiracy theorists that believes this to be plausible. I've got a copy of the S&W forum "lock" thread ratholed somewhere and the reports seemed to be disproportionally represented in earlier years. Sheer speculation, though.

April 27, 2009, 10:57 PM
On the S&W Forum, there is a very nicely done thread (with pictures) on how to remove, disable and nearly remove any evidence of the prior presence of the dreaded Lock. And it's all reversible, nothing permanent.

April 28, 2009, 03:17 AM
I hear S&W is supposed to be phasing the lock out.

April 28, 2009, 07:29 AM
I hear S&W is supposed to be phasing the lock out.

I heard that too. It was based on an article that was never written by an author who said it never happened.

And the Wiki entry is still showing the bogus Mas Ayoob reference - and people wonder why I won't let my kids use Wikipedia as a primary citation.

April 28, 2009, 01:40 PM
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 ( :scrutiny: ) 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. :uhoh: 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.

April 28, 2009, 03:41 PM
I ground some holes inside the hammer body, to lighten the hammer. This was done to reduce the lock time and helped lower the DA pull.
It also removed the engaging area of for the lock to work.
This might be a problem for some who depend on the lock, as it could be twisted to the lock position, but not locked.

April 28, 2009, 03:50 PM
I ground some holes inside the hammer body, to lighten the hammer.

This can result in ignition problems if you get the hammer too light, result in getting a "click" instead of a "bang" when you pull the trigger. Not a good procedure to recommend for novices.:uhoh:

April 28, 2009, 05:57 PM
1. How exactly does the S&W internal lock engage itself?
Since I haven't seen anything definitive, time for some technical speculatin'.

In the case of airweight revolvers chambered for artillery rounds I pictured some massive rearward acceleration followed by the frame impacting someone's hand

- for a few microseconds we get a buttload of rearward "g" forces as rearward velocity is shed. "Back and up" I believe is where the flag and lug want to go to engage the lock. It overpowers the spring and, if the hammer is fully forward or nearly fully back, it goes into the corresponding hammer recess and ties up the works.

Even assuming we dismiss out of hand those cases where the hammer ties up in the rearward position it makes for a fine mystery (how did it get there?). If the hammer ties up fully forward we haven't violated any laws of physics.

I once made an effort to ascertain hammer position in "flag up" ILFs in the S&W forum thread but it wasn't clear in many cases.

The "classic" M. Bane report:
On the second round, the "flag" part of the locking system flew up and locked the gun up at almost a full cock.

I couldn't unlock it; I couldn't uncock it; I couldn't get it to fire.
Bold mine.
That hammer mystery is a killer. Reading the report makes me think "hammer rebound under recoil" but I'm guessing there's another explanation. Beats the slap out of me what it might be, though.

It should be noted that, though I would cheerfully trust Mr. Bane with the life of my firstborn, his specific 329PD had recently returned from a trip to Jim Stroh of Alpha Precision. As certain as I might personally be that Mr. Stroh put the lock back as he found it (or didn't touch it) it makes the most circulated of the lock self-engaging reports a bit less "clean" than it might otherwise be.

Naturally, the weaker the spring (or if it's missing for whatever reason) the less recoil would be needed to get the locking piece flopping about in there.

April 28, 2009, 06:50 PM
Even assuming we dismiss out of hand those cases where the hammer ties up in the rearward position it makes for a fine mystery

Some very experienced shooters have noted that the monster rounds in X-frames can cause the trigger finger to pull back on the DA trigger under recoil, causing the hammer to come back at least part of the way without any actual "rebound". This could be one explanation.

BTW thank you all for this great thread!

There are situations where I'd LIKE to use my locks, but only if they won't cause the gun to seize up.

Both my trail gun and my pocket gun have them. In my vicinity are various Federal lands, some administered by NPS. For that and other reasons, I find myself looking for a way to store a gun in the car in a "disabled" state.

This is easy enough with a bolt-action rifle, breakdown shotgun, single action revolver or semiauto. But a DA revolver is not so easy to do on an impromptu basis.

I don't plan not to carry, on the chance that I'll end up going for a hike at some point in my travels, on some NPS land. But I want to have easy access to CYA measures if need be.

April 28, 2009, 07:51 PM
I think the limited production runs made from some older pre-ILS J-frame parts inventory has spawned a number of rumors, too
Please understand that the 642 is now a standard catalog item without the lock. These are not older Pre-ILS frames: they are current production 642-2 frames without the ILS hole, and without the ILS internals (of course).

April 28, 2009, 08:13 PM
It is my understanding that the lock only engages itself on light guns with heavy recoil and even that is exceptionally rare.

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