Installing the Marauder Hammer Debounce Device (HDD) – Part II

Monday, September 19, 2011

Part I showed you how to disassemble the Marauder in preparation to installing the HDD. In Part II, you’ll learn how to install the HDD. The numbering of steps follows in sequence from Part I.

5. Now, insert the vinyl Installation Tube provided in HDD kit into Bolt hole at the rear of the Breech. You’ll notice that the tube has an asymmetrical flare on one end. Steve calls this the Retention Tab; I call it the “fish lip.” Insert the tube into the hole at the back of the breech so that the fish lip is protruding from the breech and pointed downward, per the picture below:

Next, using a screwdriver or allen wrench, push the vinyl tube forward until about 1/2″ emerges into magazine slot in the breech. Flip the breech over so that you can see the underside. You should be able to see the vinyl tube visible through a slot under the breech. With pliers or an allen wrench, pull the fish lip so that it sticks into the slot, roughly flush with the edge.

The picture below shows the fish lip in the slot, but the aft end of the tube should actually be about a half inch further toward the muzzle.

6. Remove Screw #25 from Hammer #40. This will require use of the 9/64 allen wrench. Screw #25 will not be reinstalled – the place it occupied will be used by the HDD. Set it aside in case you ever want to return the Marauder to factory trim.

Next, set HDD with its ball bearing fitting into hole exposed by the removal of screw #25, with HDD concave side facing toward the muzzle end of the Marauder.

7. At this point you need to hold the Marauder very steady because, as Steve puts it, “the only thing holding the HDD in its proper position at this moment are Happy Thoughts.” Of  course, once assembly is completed, the HDD will be securely captured and locked in position between hammer and bolt.  But for now, it’s a little precarious.  If you removed the barrel from the barrel band, slide the barrel back into position now. Next, very carefully, lower the breech onto the air tube, taking care that HDD enters the slot on the bottom of the breech, and the Transfer Port Sleeve #19 slides into its port in the breech. Make sure that both Breech Gaskets #29 are in their correct positions before completing this operation. While bringing the breech back down onto the air tube, I found it helpful to use a small flashlight to locate the hole that the transfer port sleeve should slide into. The Big Trick here is to complete this operation without knocking the HDD out of position.  Remember to keep thinking those “Happy Thoughts!”

8. Once you have the breech back on top of the air tube, replace Screws #31 and (both) #36 screws. Screw #31 tends to fall off the allen wrench, so insert the allen wrench as firmly as possible into the screw head before lowering the screw into position. Below is what the completed assembly should look like.

9. Gently slide the vinyl Installation Tube back until contact with the HDD is felt.  Apply gentle but firm finger pressure to end of Tube to hold HDD in position. The picture below shows the approximate position of the installation tube when it is touching the HDD.

10.  While holding the bolt handle in a vertical position, slide the Bolt #9 into Breech #8, so that Bolt passes over HDD and contacts Installation Tube.  While applying counterpressure on Installation Tube to hold HDD upright and in position, continue sliding Bolt so that Installation Tube fully emerges into the Magazine slot. Shine your flashlight on the vinyl tube in the magazine slot. If you see the bolt probe protruding into the vinyl tubing, you know that the bolt has passed over the HDD. (The function of the installation tube is simply to hold the HDD in position while reinserting the bolt into the Marauder.)

11. Using care not to damage the Bolt probe, with long-nose pliers or similar tool, pull the Installation Tube out and free of the Breech. I used a small screwdriver to tease the end of the tube out of the magazine slot and then grabbed it with needle nose pliers.

12.  Replace Plunger #7. Note: the plunger controls how easy to hard it is to rotate the bolt. You don’t want to tighten it as hard as you can. Tighten it a little, test the results, and retighten or loosen as needed. Next, replace Screw #26 and Bushing #24. If you keep the Marauder upright, you run the risk of the screw and/or bushing slipping off the allen wrench and disappearing into the innards of the gun. Instead, invert the gun so that you are inserting the screw upwards. That way, if it falls, it will fall out of the Marauder.

13.  Check your work. With the gun fully reassemble, slide the bolt all the way home. You’ll probably notice some friction as the bolt slides over the HDD. Since you cocked the Marauder when you started this installation, flip the safety off and pull the trigger. The gun should fire.

Next, cock the Marauder. (If it won’t cock at all, the HDD is probably out of proper position, and you need to retreat to step 7 and start again from there.) You may notice that the cocking effort is extremely high during the first dozen or so shots, but the effort drops noticeably as the HDD assembly wears in. Congratulations, you’re done! You now have a Marauder that will deliver more shots per fill because it wastes less compressed air, and it will shoot more consistent velocities as well.

Til next time, aim true and shoot straight.

–          Jock Elliott


  1. David Scott says:

    Thanks for the installation guide. I installed an HDD on a .177 and .25 Marauder with no problem. What I don’t understand it what the device does to prevent the hammer bounce. Is it simply friction against the bottom of the bolt?? If so, does that friction not reduce the hammer speed when firing?? Inquiring minds like to know.

    1. Jock Elliott says:


      Steve, the designer of the HDD, says: “On the forward stroke, the acceleration of the hammer flips the sprag back into its “free-wheeling” position, adding minimal resistance to the hammer’s motion. But when the hammer strikes and rebounds from the valve stem, the sprag flips forward and generates downward force in reaction to its contact with the bottom of the bolt. This forces the hammer against the bottom of the tube, creating friction that arrests hammer bounce. The action is basically the same as in a common sprag overrunning clutch on a starter motor.”

      1. David Scott says:

        Good explanation. Thanks a bunch.

  2. Mike says:

    I just installed the HDD on my .177 marauder, it was easy to do I got it right the first time and it works great. I would like to know if the HDD for the discovery that you sell works ask good?
    Thank you

    1. Jock Elliott says:


      The HDD for the Discovery provides similar benefits as the HDD for the Marauder.

  3. Jeff says:

    I would like to buy the HDD kit for a Marauder .25. Can you send me details on how to purchase please.
    Thanks, Jeff

    1. Jock Elliott says:


      Contact the folks at

  4. Bill says:

    The ball in mine just falls out. is this supposed to happen? Purchased it from AOA a while back and has been working very well. it just stopped working thought and this is what I found.

    1. Jock Elliott says:


      According to the inventor of the HDD, “When the HDD is out of the gun, the Pivot Ball is retained in its socket only by the precision of fit. If it comes out (which can happen and is perfectly normal), the fix is to simply reinsert it. Effectiveness will be unchanged – same as new. Adding a dab of thick lubricant (grease) will aid retention while the HDD is being handled. When the HDD is in place in the assembled breech, the ball is positively held in place by the hammer and can never escape.”

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