Fractured sear on a new 640 Pro

[Old_Blue]

Hello, all. New member here, but not new to S&W firearms. Finally have something noteworthy to contribute, after reading this forum for years.

Today I was dry-firing my 640 Pro, bought new less than a month ago, when the trigger jammed to the rear. There were no visible obstructions to the action externally, so I opened up the gun.

The sear mechanism was stuck in a position that prevented the trigger from returning. The sear wouldn't pivot on the spring-loaded hinge that holds it onto the hammer. When I shook it a little, a metal fragment fell out of the gun.

It appears that this little wedge-shaped bit of metal, about 1 x 1.5 x 3 mm, had broken off the sear. The metal has a granular appearance at the fracture point; it looks like the kind of failure I've seen in weak, brittle metal in various products of all kinds during my lifetime.

The revolver is headed back to S&W tomorrow. Hopefully for a reasonably fast turnaround. I understand defects happen; thankfully this failure didn't happen in an emergency. The followup from customer service is what will make or break my lasting impression.

 

[L-2]

Disappointing news. Great photos and description of the problem. I'll look forward to hearing back from you (Old_Blue) on this thread. I estimate ~3 weeks.

 

[OLDSTER]

I'm certain S&W will make your 640 good. What will be interesting is their explanation for the defect ? BTW, welcome to the forum from North Dakota .

 

[muddocktor]

Mmm, looks like a MIM part that didn't cook quite right. Disappointing. I'm sure S&W will make it right for you.

 

[Wishbone]

Sorry about your troubles. I hear about more problems with the 640 pro than anything else for some reason. I wonder if that part can be replaced with non mim?

 

[scooter123]

Mmm, looks like a MIM part that didn't cook quite right. Disappointing. I'm sure S&W will make it right for you.

Actually it's an MIM part that was mis-handled. The compacted form prior to Firing is EXTREMELY FRAGILE and if mis-handled at all can crack. What we are seeing is the result when a partially cracked "green" part is then fired. A very weak part that can crack at any time because it already has a "built in crack".

 

[steelslaver]

Yes that is some huge grain structure. Should not look like that at all. Something went wrong i the process somewhere.

Before the MIM haters start in, think about this.

I purchased 6 2'x3' pieces of high grade German D2 tool steel 3/16" thick. This was rolled sheet so it had been "forged" repeatedly in the process from taking it from a billet to sheet. I had 2 sheets of it water jet cut to a pattern I use to make my standard hunting knife. On one of the blades after grinding the bevels and working to 400 grit sanding there was a small line that would not sand out. I took it back to the belt sander and it still remained after hitting that area again. Put it in a vise and applied side pressure. Snap and at the break an inclusion was visible. Forged is not immune to failure either. This was a steel that was poured into a billet from an inert atmosphere, induction oven, before being hit with the hammers and rollers to reduce it. Top shelf processes by people who pride themselves in their abilities.

 

[Old_Blue]

The revolver shipped out from S&W today, 13 days after they received it. Looks like it will be a 17-day turnaround.

 

[F75gunslinger]

SO my two questions are,

"What did they say?" and

" Were you using some type of snap cap?"

 

[HamHands]

Hello, all. New member here, but not new to S&W firearms. Finally have something noteworthy to contribute, after reading this forum for years.

Today I was dry-firing my 640 Pro, bought new less than a month ago, when the trigger jammed to the rear. There were no visible obstructions to the action externally, so I opened up the gun.

The sear mechanism was stuck in a position that prevented the trigger from returning. The sear wouldn't pivot on the spring-loaded hinge that holds it onto the hammer. When I shook it a little, a metal fragment fell out of the gun.

It appears that this little wedge-shaped bit of metal, about 1 x 1.5 x 3 mm, had broken off the sear. The metal has a granular appearance at the fracture point; it looks like the kind of failure I've seen in weak, brittle metal in various products of all kinds during my lifetime.

The revolver is headed back to S&W tomorrow. Hopefully for a reasonably fast turnaround. I understand defects happen; thankfully this failure didn't happen in an emergency. The followup from customer service is what will make or break my lasting impression.

Smith will fix it, on their dime as well as shipping both ways with a quick turnaround. The only caveat is... they will replace that sear with one from the parts bin that was made the same way the broken one was made. Hopefully, the sear that broke had a serious defect or heat treatment during the sintering process how they make them and this IS a freak accident. If it happens again I'd swap that part with an aftermarket sear that is forged.

I'm swapping in an Original Precision "Steel Unlocking Bolt" in my 625-5 Mountain Back Packer I'm now starting to carry a lot in place of my M29-3 for the Woods and at night walking the dogs... I'm 90% sure the MBP currently has an MIM unlocking bolt but haven't had the sideplate off to confirm yet. However, when installing Original Precision Lock Deletes on my M629 Talo and M625 (both now sold to my little brother), you have to take the Bolt out as it's in the way. Upon looking at the factory bolt more closely, scrutinizing it's heavy flashing at the MIM seams; and more alarming, the smaller radius where the pivot stud attaches to the bolt... It "appears" to be a rather fragile part. I'm ordering it today... and if my 2000' manufactured M629-5 has the same Bolt my 625 and "Talo" has/had... It will be swapped. If it doesn't have the MIM bolt I'll put it in the stock bin.

 

[HamHands]

The revolver shipped out from S&W today, 13 days after they received it. Looks like it will be a 17-day turnaround.

Not the fasted turnaround I've ever heard of but that isn't really bad!

 

[HamHands]

Yes that is some huge grain structure. Should not look like that at all. Something went wrong i the process somewhere.

Before the MIM haters start in, think about this.

I purchased 6 2'x3' pieces of high grade German D2 tool steel 3/16" thick. This was rolled sheet so it had been "forged" repeatedly in the process from taking it from a billet to sheet. I had 2 sheets of it water jet cut to a pattern I use to make my standard hunting knife. On one of the blades after grinding the bevels and working to 400 grit sanding there was a small line that would not sand out. I took it back to the belt sander and it still remained after hitting that area again. Put it in a vise and applied side pressure. Snap and at the break an inclusion was visible. Forged is not immune to failure either. This was a steel that was poured into a billet from an inert atmosphere, induction oven, before being hit with the hammers and rollers to reduce it. Top shelf processes by people who pride themselves in their abilities.

Solid post and I fully agree that forgings are not immune to improper manufacturing. I don't hate all MIM parts at all. But situations like in the OP's is exactly why I put 250 full house loads thru my new or new to me revolvers and at least 500 thru any semiauto before strapping it on my side. I like to get 500 or so dry fires as well (using AZoom snap caps ofcourse), thru any new to me pistol/revolver! If anything is going to break or hiccup it's probably going to happen during the above break in. Sounds like the OP was on his way to doing exactly what I do in regards to dry-firing.

 

[Tom S.]

Yes that is some huge grain structure. Should not look like that at all. Something went wrong i the process somewhere.

Before the MIM haters start in, think about this.

I purchased 6 2'x3' pieces of high grade German D2 tool steel 3/16" thick. This was rolled sheet so it had been "forged" repeatedly in the process from taking it from a billet to sheet. I had 2 sheets of it water jet cut to a pattern I use to make my standard hunting knife. On one of the blades after grinding the bevels and working to 400 grit sanding there was a small line that would not sand out. I took it back to the belt sander and it still remained after hitting that area again. Put it in a vise and applied side pressure. Snap and at the break an inclusion was visible. Forged is not immune to failure either. This was a steel that was poured into a billet from an inert atmosphere, induction oven, before being hit with the hammers and rollers to reduce it. Top shelf processes by people who pride themselves in their abilities.

Any one with a nominal gear head background will be able to regurgitate stories about failed cranks and rods that were forged. Anything man made can fail - forged, MIM, billet or cast - it doesn't matter. It's too bad records haven't been kept but I'd bet that MIM part failure and forged part failure numbers would be pretty close to being even.

 

[Breakaway500]

Excuses and MIM parts seem to go together. Same thing with castings and PMPs (powdered metal parts)

I'll stick to forged internals on my race motors and in my firearms,if given the choice. 45 years turning wrenches have taught me a few things..

 

[GerSan69]

I'm no scientist, but I've read a lot about MIM, Forged parts, etc., and it seems like there is just a whole lot of misinformation running around about metallurgy on this internet (Like probably 100% of all topics discussed, right?)
Bottom line to me is that other than tradition, there's just no reason to think forged is "better." A nice case-hardened trigger or hammer is prettier than MIM, but the MIM will have a more consistent, uniform finish right out of the mold with little to no hand finishing required.
Since my guns aren't sitting around in picture frames, I don't care about pretty triggers. As long as it's got the S&W monogram, I'm happy. Thanks for reading!

 

[Old_Blue]

I've been a serious user of snap caps, for obvious reasons, since acquiring my 686-3 and 29-5 a few decades back. That habit carried over to the 640 Pro for the proverbial thousand-dry-fire "trigger job." After that was finished, I double-checked S&W's online FAQ to see if they were absolutely sure that their new revolvers could handle dry-firing without any stated limitations. That's what they said, so I decided to give it a shot. The day the sear broke, I wasn't using snap caps.

For comparison, some of my other revolvers:
LCR No. 1 -- 1,000+ dry fires, no snap caps, no problems
LCR No. 2 -- 1,000+ dry fires, no snap caps, no problems
Super Redhawk -- Hundreds of dry fires, no snap caps, no problems.

I would be reluctant to assume S&W is wrong about the ability of its revolvers to withstand dry-firing without snap caps, when my LCRs, whose internal parts seem less solidly built than the 640 Pro's, can handle it without concern. If the paperwork that arrives with the gun lacks details, I'll be calling Springfield to find out whether they have any theories beyond chalking it up to a random defect.

 

[F75gunslinger]

I look at snap caps as cheap insurance. Why beat up the firing pin and internals when you can get a set of snap caps for less than $30 in most cases. No different than not letting the slide slam closed on a semi-auto with the slide release when there is no magazine. It just beats up the internals. Can it be done ? Sure. Will it damage anything ? Not occasionally. But do it enough and you're putting undue wear on things that are easily avoided.

 

[Ribwizzard]

It does seem funny the the 640 pro has more than its share of problems.
I looked at one in a LGS, action was completely locked up with trigger stuck back and hammer stuck down. Owner offered it to me for $500 but said that I would have to send it off myself for the warranty work. I passed

 

[Old_Blue]

The revolver is back. Here are the results of my inspection and an eye-opening follow-up talk with S&W customer service.

The sear and its spring were replaced. The gun was returned clean and well-packaged. The action was fine, except that the trigger return was a little sticky. Some lubrication and dry-firing -- with snap caps -- cleared that up.

Now to the really interesting part. I phoned customer service for any details or advice about the sear failure. I spoke with a fellow who said that although he was relatively new to the customer service side, he had come there from a job in the factory.

When I described the circumstances of the sear failure, he told me he was trained to advise customers to NEVER DRY-FIRE WITHOUT SNAP CAPS.

I pointed him to this, from S&W's online FAQ:

"Can I dry-fire my Smith & Wesson?

"Yes, except for the .22 caliber pistols [and] .22 caliber revolvers. . . ."

. . . with no mention of the need for snap caps.

He seemed genuinely surprised. Slightly appalled might be a better term.

Anyway, I left it at that. It was a polite discussion, and I came away convinced that the dry-firing was responsible for the breakage.

Beware of online FAQ's. Or trust but verify.

 

[muddocktor]

Old_Blue, looking at the pic of the fractured sear you posted, I can be pretty certain that your problem was not caused by dry firing. That part was defective, for whatever reason. I would hazard a guess that any breakage caused by dry firing would be related to the floating firing pin or spring, not the other internals.