Death of a Trigger Pack: Timney Tavor Bites the Dust

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This is a sad story. During the last 3-Gun of the season, a team match, I was having a whale of a time blasting away with my Tavor. I dropped into prone to start ringing 200 yard gongs, and got a click with no bang. Cycle the gun manually, squeeze again, same result! I cycle twice more before I give up, pick up my partner’s AR-15, and finish the stage. It sucked.

Upon disassembly the cause was pretty darn obvious: something was rattling inside the gun, never a good sign. The hammer from my Timney Trigger pack had sheared clean off during the stage. You might remember my review from early last year.

Now, I have a theory as to why this catastrophic failure happened, but I’ll save that for after the gory photos. Scroll down, and see if you reach the same conclusion I do. Perhaps someone with more metallurgical knowledge than me can see some indicators in the break.

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The two marks inside the body of the trigger pack say to me that the hammer was over traveling and impacting the inside housing. And clearly it wasn’t built to take that kind of stress.

My working theory as to why this pack failed comes from the fact that I’m shooting it in a TAR-21 rather than a SAR-21 rifle. You see, Canadian Tavors are still built on a semi-auto receiver, but they are 100% Israeli made.

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As a result, our bolt carrier groups look a little different from the SAR-21 family.

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If you look closely, there are two flanges on the bottom of a TAR-21 bolt carrier group, which would normally engage the auto sear on the IDF select-fire version of the rifle. Like an AR-15, this full auto BCG is only a small part of actual automatic fire, but it was removed from the US rifles. I suspect these flanges are applying pressure to the Timney Trigger pack, forcing it deeper into the housing than was intended.

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It’s the kind of problem you’d never see until you put the pack into a different rifle, but it’s still disappointing to see a fancy bit of gear fail like that, particularly when the clock is running.

A spot of good news? With the Giessele lightning bow installed, and my factory IWI trigger pack, I get a crisp, consistent 5.5lb single stage pull. That’ll do for me.

I also recently had the opportunity to gather 20 Canadian Tavor owners together for an IDF Tavor course and survey a few different trigger packs. We couldn’t find similar impact marks in the Super Sabra and Shooting Sight trigger packs, but many of those rifles had seen less than 1000 rounds.

For Tavor owners outside the USA, I’d encourage a regular check on your after-market trigger pack to avoid a disappointing click and no-bang.

Update: Thanks to everyone who mailed me theories on what happened? This one seemed particularly well put together…

“Fatigue originating from the corners of the thin webs at the back of the hammer.

The two cracks grew towards the front and merged, creating the step front and center. The initiation of two independent cracks at separate locations with similar geometry make the idea of any material flaw quite unlikely. Instead it is highly probable that the geometry is the problem, creating a high stress location that just begs to initiate cracks.

The observation that the hammer seems to be over-travelling and hitting the housing on its backstroke is significant, as that action would be expected to impart a bending moment on the hammer that would put the back edge of the hammer in tension, while striking the firing pin would stress the hammer in the opposite direction, putting the back edge of the hammer in compression. The hammer would be much less likely to crack from the backside without that contact with the housing. Also fatigue where you have reversing loads is much more severe than simply having loading in one direction only, which helps explain why all this happened in only a couple thousand rounds.

I don’t see anything that strongly suggests how the part was made, and the dimple-textured surface on unmachined areas could be the result of investment casting, forging or shot blasting/peening.

I am not a 5th mechanical engineer, but I do have this here metallurgical engineering degree, and did spend about a decade doing failure analysis. I hope that counts for something.”

 



Edward O

Edward is a Canadian gun owner and target shooter with a Bachelor’s Degree in Journalism. Crawling over mountains with tactical gear is his idea of fun. He blogs at TV-Presspass and tweets @TV_PressPass.


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  • bull

    it seems that the hammer might be hardened a bit too much too…

  • Nicholas Chen

    Yikes! What a way to find out.

    • DIR911911 .

      better at the range than possibly defending the house

  • David

    There’s competition triggers and there are durable triggers. Choose wisely

  • thedonn007

    Did you contact Timney? I am sure that they would send you a replacement.

    • JamesRPatrick

      Wouldn’t do him much good, but a refund or credit would be nice.

    • I’ve dealt with Timney before, and they’re definitely willing to look after their products and customers! I waited 60 days from contacting them to publish this, and haven’t heard back as of writing. The problem is just like James says below: I’m not sure if a replacement would actually fix the issue.

      • thedonn007

        I am really suprised that they have not contacted you about this issue yet. I have had good experience with their customer service.

        • kgallerno

          I’m sure after reading this article on TFB, Timney will start checking their garbage can on their computer to find Edward’s email to resolve the issue now.

        • I’ve had great experience with their customer service too! I did a tour of their facility back in 2014 that was fantastic: (http://www.thefirearmblog.com/blog/2014/11/21/a-look-inside-timney-trigger-manufacturing/)

          In this case I’m sure if I’d needed a repair or replacement I could have had that happen very quickly with either a phone call or a follow up email.

          But the closer I look at this issue, it could just be that their trigger isn’t going to be compatible with my rifle. I’m not butt hurt about that.

          I’m sure they’d fix it, but if this really is a compatibility issue that will continue I don’t think it would be good for them or for me to come back every six to eight months asking for a replacement trigger over and over and over!

    • JSmath

      I am more than certain that given the circumstances, Timney would be willing to try and re-engineer a drop-in unit so that it works with either the different or both designs.

  • George Herbert

    Can you take a closeup of the broken off piece at the fracture line? And the remaining part?

    I’m not a metallurgist but had most of a ME degree in college including materials science. It looks like a brittle fracture. So, over hard and too many impacts, or way over hard. Most gun materials should yield some. That looks just cracked…

    • George Herbert

      Also… What’s the exact normal point of contact with the firing pin? Can you mark that?

    • OBlamo Binlyen

      Having spent 35 years in the machining trade and having seen some bad heat treat and stress fractures that was my thought when I saw that one photo.

  • Oldtrader3

    The hammer is obviously a MIMS part and it does appear that the hammer is being struck from behind by something. Also, I think, that part of the problem is part design as well? The hammer could have larger radii in the bottom corners which would relieve stress risers on the inside of the part which is where the part failed.

    • Along the same line as my though. When something is machined to a perfect square corner the corner is usually the stress point that will fracture.

    • Rick5555

      That’s not a MIM part. It’s not forged either. It’s from billet. What type steel hard to say. The hammer was over harden and probably not stressed relieved.

  • Thomas Gomez

    The only after markets I will use are ALG or Geissele.

    • phacops

      Geissele is having broken hammer problems too. It’s sad that for the price these companies charge that they would ever let such a critical part get out of their QA department. And why in the world are they not having a recall – this is a critical part. I only have the trigger bow but if I had a trigger pack – I would demand a swap. Looks like the plain stock $99 trigger is a lot more dependable than a $350 one. Sad.

  • Jim

    Many years ago I worked for Westinghouse Research doing destructive testing. This is a failure of either metal selection or heat treatment. There are at least 4 fracture cycles in the one photo. What I can’t tell from the photo is there any discolorations (even a small line) that would indicate a crack that grew over time.
    If there is no discoloration the selected metal is most likely to hard and the crack grew that very day as any solvent from cleaning would would leave marks in the forming cracks.
    If there is no discoloration, the two fracture lines along the top (curved profile) would seem to indicate either flame hardening or to short of time in the oven. Both cause a hard outer surface that would produce the very small initial fracture lines.
    Jim

  • Misa Miodrag

    I wonder what would happen if you use a stock SAR trigger in a Canadian TAR21, if it too could snap like this.

  • K R

    I originally came to the conclusion that the metal was over hardened as well, but the reverse forces of the hammer striking forward whilst being pushed rearwards when striking the firing pin makes just as much stress probably even if the metal was not over hardened. The conclusion above that you chose makes the most sense I think. Hopefully they will make an adjustment to their trigger for our neighbors to the north.

  • Hyok Kim

    A chance one takes whenever one uses aftermarket parts.

  • Ryan Jennings

    Well before the failure, while running properly…. Do you prefer the Timney or Geissele ? Unbiased answer now knowing the Timneys breaking points. I ran a Timney 3.5lb in my MK12 . I switched to a Geissele 2 stage ssa-e . I like the Geissele but dropped the Timney back in the MK12 , and used the ssa-e in another rifle all purpose is why I’m asking.

  • 10x25mm

    Crack is definitely a fatigue fracture. Crack travel path was from the top surface (when the hammer is cocked in the unit), downwards. Dual initiation sites extremely rare in fatigue cracking and not in evidence here. Suggests high tensile stresses were created by dry firing / live firing contact of the hammer impact face with the rear of the carrier, not any downward pushing effect by the auto sear trip flanges on the carrier.

    Not possible to recommend corrective actions without more information on the metallurgical processing of the part, but it would certainly benefit from improved section transition radii. Hammer has an inset boss which suggests it was fabricated by MIM. If so, debinderizing and sintering practices are critical in these shock loading applications.

    This kind of crack is easily found before failure by dye penetrant inspection (ASNT Code: PT). Simple PT test kits are readily available at industrial suppliers, but you can achieve the same effect with a high penetrating oil (I use red dyed penetrating oil sold to loosen rusted nuts) and chalk or talcum powder. Just wipe down the hammer in the area where a crack is suspected with the penetrating oil. Vigorously wipe the excess oil off the surface with the fluffy, absorbent side of dry bore patches. Dust with chalk or talcum powder and set it aside for 30 minutes. Then examine the dusted surfaces. If you see an oily line in the dust, your hammer is cracked under the oily line. This method was known as ‘oil and whiting’ when it was developed back in the 19th Century. Still useful today.

  • BigFED

    The AR-180 had a similar problem with folks who would “fire” their rifle with it hinged open or the upper/lower separated. If the trigger was pulled while the upper/lower were NOT in closed, the hammer would hit the last round bolt open lever and after enough times that lever break/fail. One of the first things I used to tell the owners of any AR-180 was to NOT PULL THE TRIGGER WHEN THEY HAD THE RIFLE HINGED OR SEPARATED. It wasn’t a matter of “if” it was going to fail but, when!

  • l2a3

    Let me understand this: You took a mechanical device made for a different firearm and used it in the not designed for firearm and it broke.

    The way the title reads is that “Timney trigger pack” is going out of production, not that you discovered/found out that the SAR 21 trigger pack may fail if used in the TAR 21 Rifle.

    The article is interesting but the title need rewording/correcting, because it leads the reader to a different understanding before the article is read.