Hatsan Bully – Hammer Spring Tension Screw adjustment (7 photos)

Forums PCP Airguns Hatsan Bully – Hammer Spring Tension Screw adjustment (7 photos)

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    Rich7777
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    I’ve been meaning to create a “How To” adjust the Hammer Spring Tension (HST) screw on a Hatsan Bully, but have been having fun on the range at IndainaAirguns.com :)
    Anyway, I thought I better do it now or I won’t get a chance for a while. 

    Cliff Note: You have to separate the stock from the action (gun) to access the locking grub screw for the HST screw and the HST screw. 

    Step 1
    Safety first.
    Always keep the muzzle of the airgun pointed in a safe direction. Unload the magazine from the Bully. Ensure there is not a pellet chambered. Ensure the Bully is uncocked. Put the safety on. 
    I actually shot mine down to empty. There’s no pressure in the gun. I did this so I can tear it apart and see if I can get a regulator in it. You don’t have to empty the air from the cylinder. 

    Step 2
    I recommend you tilt the Hatsan Bully on its side as shown in photo below. If you don’t, you’ll be hunting for springs in just a minute … not that this would happen to me ;)
    Press the cheek weld adjustment button in and simultaneously pull the cheek weld completely out.

    Step 3
    Remove the Cheek Weld adjustment button carefully. There are 2 springs underneath it (see arrows in photo below). Remove and store the springs in a safe place.

    Step 4
    Turn the rifle upside down. Locate the first of two stock screws. The first is next to the manometer. It’s a 4.5mm hex screw. See photo below. Remove this screw.

    Step 5
    Locate the second stock screw right behind the magazine storage compartment. It’s a 4.5mm hex screw. See photo below. Remove this screw.

    Step 6
    Take your time, and slowly rock the stock loose from the action. (see below). The first couple of times, it’s tight. I’ve done it so many time now, I have no problems getting it on and off.

    Step 7
    The Hammer Spring Tension (HST) screw is locked into place by a 2.5mm hex grub screw on the side of the gun (see arrow in photo below). This grub screw has to be backed almost all the way out in order to allow the HST screw to be adjusted. If you’re trying to to adjust the HST screw and it won’t turn … this is most likely why.

    Step 8
    Looking at the back of the gun, there are 3 holes. The HST screw is the bottom hole (see photo below).
    Clockwise will increase hammer spring tension pre-load, which will increase your velocity / FPS
    Counter clockwise will decrease hammer spring tension pre-load, which will decrease your velocity / FPS
    I believe this is opposite of older Hatsan airgun models. 

    Step 9
    I use a caliper to measure the depth from the back of the gun to the top of the hammer spring tension screw. I’ve been careful not to fall into the slot of the screw. Record your depth with your shot string results for future reference. 

    Step 10
    Re-assemble in reverse order. 

    -Rich
     

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    cootertwo
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    Thanks for the tip. I’ve got a Bully in 35 cal. Still tinkering.

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    ironlion269
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    @rich7777, very good use of graphics to point out the details of your instructions.  Some day instruction “booklets” will instead be flash drives or some other digital doodad that will provide both text and video to buyers.  Seeing the operation is so much better than just reading about it and then trying your hand at the screws.  Nice job!

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    Rich7777
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    “cootertwo”Thanks for the tip. I’ve got a Bully in 35 cal. Still tinkering.


    Bully in 35 cal. I bet that thing hits like a freight train. Looking forward to hearing about your experiences.

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    Rich7777
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    “ironlion269”@rich7777, very good use of graphics to point out the details of your instructions.  Some day instruction “booklets” will instead be flash drives or some other digital doodad that will provide both text and video to buyers.  Seeing the operation is so much better than just reading about it and then trying your hand at the screws.  Nice job!

    Thank you ironlion269. I appreciate the feedback! I think you’re right about the electronic doodad, whatever form that may take. I know I would appreciate it. 

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    E30_S50
    Participant
    Member

    Thanks Rich. This info is very helpful. 

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    Rich7777
    Participant
    Member

    “E30_S50”Thanks Rich. This info is very helpful. 

    Anytime, glad to help.

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    PelletPusher
    Participant
    Member

    “ironlion269”@rich7777, very good use of graphics to point out the details of your instructions.  Some day instruction “booklets” will instead be flash drives or some other digital doodad that will provide both text and video to buyers.  Seeing the operation is so much better than just reading about it and then trying your hand at the screws.  Nice job!

    
YouTube how-to videos have replaced all books and manuals for me.  

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    Imold
    Participant
    Member

    Thanks for the info Rich, much appreciated.

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    PelletPusher
    Participant
    Member

    How is the Bully shooting for you Rich?  Please share some photos and thoughts! 

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    Rich7777
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    Next time I get out to the range, I’ll take some photos. Might be tough this weekend with Father’s day.
     

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    Bigragu
    Participant
    Member

    Hey, Rich, I’m curious as to the effects on velocity that hammer screw does for say, 1 whole turn CC, or even half a turn? Also, if backed all the way out, will the spring pop out should one want to try different springs?

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    Rich7777
    Participant
    Member

    On my .25 cal Bully, I ended up backing the Hammer Spring Tension (HST) screw out almost 1/2". I don't know about the power impacts by measuring turns. To set the power where I wanted it, I set my pressure to 3000 psi (just a little above 1/2 the shot pressure range) and started shooting and adjusting the HST screw until I got the FPS where I wanted the top of the shot curve. I was careful to keep the pressure between 2800 and 3000 psi. while I made the adjustments.   

    Side note: The HST screw is notched to allow the locking grub screw to seat into one of the notches. If you don't have one of the notches on the HST screw aligned to the locking grub screw, the grub screw won't fully seat. The grub screw will stick out from the side of the action and you won't be able to get the stock back on. 

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    RIng
    Participant
    Member

    Thanks what are your thoughts on a regulator ?

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    E30_S50
    Participant
    Member

    I backed mine out 8 full turns and got many more shots per fill. It pushes a 25grain pellet at about 1000fps at this setting…so I could probably still back it out quite a bit more. 

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