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Thread: Hammerli 401 anti bear trap

  1. #1
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    Hammerli 401 anti bear trap

    Does anyone have a picture or parts drawing showing how the anti bear trap mechanism on a Hammerli 400 series side lever (401, 403, 420 etc) goes together? I have one or more bits missing as there's no engagement between the abt lever and the piston.

    Thanks

    Last edited by GR5688; 10-07-2024 at 09:47 AM. Reason: Add picture

  2. #2
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    Quote Originally Posted by GR5688 View Post
    Does anyone have a picture or parts drawing showing how the anti bear trap mechanism on a Hammerli 400 series side lever (401, 403, 420 etc) goes together? I have one or more bits missing as there's no engagement between the abt lever and the piston.

    Thanks

    I think so, I'll just dig them out and remind myself how to post them!

  3. #3
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    I bought a 401 and a 403 from the same guy in 2020 and they were among the first air rifles I worked on in 2021 during lockdown. They were particularly scary to work on as a novice! But having two essentially identical actions meant that I had a spare to refer to when working on the first.

    My edited notes on the 401: Took apart to service. Slightly worrying as I could find no online guide. Discovered the trigger block was held by 4 Allen screws [bolts], one of which was missing and the other barely gripped..... The trigger block is pretty temperamental. It needs to be just so... in relaxed form, off-gun, there needs to be sufficient pressure on the sear spring for the ABT pawl to be pushed down [I think I meant up] so as to engage. When [cocking] lever closed, this pushes the [ABT] lever on the trigger block forward which disengages the ABT pawl. But resist the temptation to play with it as its very easy to bend the spring which will mess everything up - and these springs really are no longer available in the UK! The trigger/ABT spring needs to be basically in a straight line when it is in place....

    That doesn't seem to make a lot of sense now, but hopefully the photos will help (they're small on this post, but click on them and they should go to a better size). Regarding the dodgy allen bolts, I had the bolt holes re-tapped to a larger size. The bolts engage the cylinder which really isn't very thick, so M3 bolts struggle as there's little thread for them to grab. Taking it to M4 did the trick but you must make sure they don't protrude into the cylinder itself or they'll snag the piston. I recall that the trigger unit bolts in both rifles had to be done up snugly against their spring washers, but not over-tightened or it just didn't work.

    When the cocking lever is pulled away from the action body, the little ABT lever on the side (which has been pushed forward slightly by the action of closing the cocking lever) rotates to the rear slightly, thanks to a long but small spring which is a combined ABT and sear spring. The ABT/sear spring is working on the underside of the ABT pawl (OR on the ABT lever - I can't remember which) inside the trigger unit, with the effect that the tooth of the ABT pawl rises as soon as the cocking lever is moved back slightly, and engages scallops in the bottom of the piston (like a TX200 has on the side of its piston) making a ratchet noise as the piston is drawn back. This is the anti bear trap. You can see the pawl sticking up (ie when the cocking lever pulled back, or when the trigger unit is removed from the action) in the centre of the photo below.



    When the cocking lever is closed, it pushes the ABT lever forward slightly as it meets the action body, and as the ABT lever rotates it disengages the ABT pawl from where it has engaged the piston, against the ABT/sear spring pressure. Then the bottom of the ABT pawl can be seen in the slot level-ish with the bottom of the trigger block where you have indicated with an arrow in your photo. Open the side lever a fraction, just so as to make the ABT lever move, and you should see the bottom of the ABT pawl move down slightly. If it does it suggests the ABT/sear spring is working. Don't push the ABT lever as far as I'm doing in this photo.



    (Shows the topside of the trigger block with the ABT pawl retracted when the cocking lever is closed)



    (Shows the underside of the trigger block and ABT pawl when the cocking lever is closed and the ABT lever is pushed way too far forward! DON'T DO THIS!!)

    Nooooo! That's too much! For goodness sake don't fiddle with the ABT lever and work it too enthusiastically - I did, and I bent the ABT/sear spring, and it took ages to work out what had gone wrong. The ABT lever is only meant to move very slightly - only a few degrees - when the cocking lever is closed, and you really don't want to move it more than that. The ABT/sear spring could be damaged in the same way if used to de-cock the rifle but as the rifle is a sidelever you'd need three hands to do this! [No, I'm wrong on that last point - there should be a little limiter thingie, held by one of the bolts holding the trigger block to the cylinder, to stop the ABT lever going to far when the rifle is assembled].



    The ABT/sear spring ISN'T meant to look like this!

    In the end I had to bend the ABT/sear spring back to more or less the right shape (see below), and get it back in (not an easy job first time) and then it worked.



    I hope this helps.

    I think your problem will most likely be with the ABT/sear spring being bent or broken.

    Apologies to anyone trying to read this as I've been editing it but I hope it makes more sense than when I started!
    Last edited by Mr Pusk; 10-07-2024 at 04:56 PM. Reason: I hope it makes more sense!

  4. #4
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    Thanks, that's brilliant. I definitely don't have all the bits then.

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    I need to take it apart again to have another look, but based on your pics I think I am missing both spring and pawl.

  6. #6
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    Quote Originally Posted by GR5688 View Post
    I need to take it apart again to have another look, but based on your pics I think I am missing both spring and pawl.
    Maybe a previous owner didn't like the noise of the ABT? Mind you, it's pretty quiet on mine.

    It may be just the pawl, because (and I haven't gone into this in my essay, mainly because I didn't look at that end at all) the other end of the ABT/sear spring bears on the end of a sear or something at the trigger end, so the spring probably needs to be there for the rifle to shoot at all.



    You should see easily enough whether the ABT/sear spring is present when you take the action out of the stock

    Last edited by Mr Pusk; 10-07-2024 at 08:37 PM.

  7. #7
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    So my gun has neither the pawl nor the spring. It cocks solidly and fires fine. I'm guessing the likelihood of sourcing the missing bits is very low, so I might as well remove the abt lever entirely.


  8. #8
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    I suppose so, though I guess keeping it would at least keep the rifle looking as it should externally, even if it doesn't actually do anything. Your call though. I guess that without the spring the ABT lever just flops about? And when the cocking lever's closed, you can't see it anyway. I take your point!

    For those unfamiliar with these rifles, they're taploaders, so the absence of an ABT shouldn't be any more of a safety issue than on, say, a Webley Mk3.

    Well I'm clearly wrong about the other end of the spring acting on a sear. I can see I'm going to have to take one of mine to bits again to work out what it actually does. Maybe it locks the trigger or something? Will report back for the sake of completeness when I've done so.

  9. #9
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    Yes, safety wise there's no reason to have any fingers in the way of the cocking lever, other than to release the abt itself which always seems a bit daft to me.

    Thanks again for the the info you have posted.

  10. #10
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    The daddy of the 400 series was the Model 3, this did not have a anti-beartrap on it. Because it was a pre-woke air-rifle.

    Then some idiots chopped their fingers and spoiled the fun.

    Its possible someone just de-trapped it, although the rifle can be decocked by holding the safety lever down. It's very important on these rifles to keep the trigger unit bolts nice and tight because if they loosen the sear won't engage far enough and it will go off on its own, either causing an involultary discharge or a dangerous beartrap incident.

    Trigger parts for these do come up on the auction site from time to time.

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