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

Monday, September 12, 2011

Note: This blog on installing the Marauder HDD is broken into two parts. Part I covers the disassembly of the Marauder prior to installation. Part II will cover the installation of the HDD itself.

Virtually all airguns that store gas under pressure (such as pre-charged pneumatics, multi-stroke pneumatics, and CO2 guns) and use a knock-open valve suffer from hammer bounce. When the airgunner triggers the shot, the hammer hits the valve and knocks it open, allowing gas to rush into the breech, propel the pellet down the barrel, and out the muzzle. So far, so good. The very next thing that happens is that the compressed gas inside the reservoir acts like a spring and pushes the valve shut, often with enough force to drive the hammer off the valve. The hammer then slams back down on the valve (this is hammer bounce) and pops the valve open again. When this happens, the gun wastes air (or CO2) and makes a louder report than necessary. Even worse, hammer bounce contributes absolutely nothing to the propulsion of the pellet downrange, since the pellet has already left the barrel before the hammer bounce occurs.

To prevent hammer bounce, a hammer debounce device (HDD) is needed to prevent the hammer from rebounding off the valve and needlessly opening the valve again. The result of installing an HDD is a flatter shot curve with more shots per fill, as shown by the diagram below.

To install the Marauder HDD, engineered by Steve Woodward and offered by Airguns of Arizona, you will need to print this Marauder Parts Diagram from Crosman Corporation:

You will also need a flat-blade screwdriver, pliers, needle nose pliers, a 3/32” allen wrench, and a 9/64” allen wrench. A small flashlight will also be helpful. Note: you don’t have to remove the action from the stock, but you can if you want to.

The HDD kit (shown below) includes the HDD itself (right) and a vinyl installation tube.

Okay, let’s get started.
1. SAFETY FIRST!   First, remove the magazine or single-shot tray, and degas (depressurize) rifle. You will be working with the rifle cocked (see below), and if you inadvertently trigger a shot with the rifle pressurized, you could (as Steve Woodward put it) “send the transfer port parts to the fourth dimension.”

2. Set the safety and cock the rifle.

3. Remove Plunger #7. This is a screw assembly at the extreme back edge of the receiver.

You’ll need the flat blade screwdriver for this.

Here’s what the assembly you are removing looks like:

Next, remove Screw #26 and Bushing #24 that is attached to it. You’ll need the 9/64 allen wrench for this, and you’ll find the screw on the lefthand side of the receiver, just aft of the magazine slot.

BIG NOTE: There is a bushing around the shaft of screw #26, and it will want to fall into the innards of the gun if it doesn’t stay attached to the screw as the screw is removed – so try to tilt the gun so that the screw and its bushing want to fall out of the gun as you are unscrewing it.

With screw #26 and its associated bushing removed, you can slide the bolt #9 completely out of the back of the breech.

4. Next, remove Screw #31. This requires sliding the 3/32 allen wrench into the hole from which you removed Plunger #7. I found I had to use pliers on the end of the allen wrench to get the screw to break free.

Next remove (both) Screws #36 using the 3/32 allen wrench. These are located on either side of the breech forward of the magazine slot. 

With screw #31 and both screws #36 removed, you can lift the breech #8 free of Tube #1. If it is easier for you at this point, you can also slide the barrel out of the barrel band, completely freeing the breech and barrel assembly from the rest of the Marauder’s air tube assembly.

We are now done disassembling the Marauder breech in preparation to installing the HDD. Next time, we’ll go through the actual installation of the HDD.

Til next time, aim true and shoot straight.

–          Jock Elliott


  1. Karl Brohan says:

    Regarding the hammer debounce device, I pulled up the hammer mod pdf from the Crosman site. It appears to only apply
    to .177 and .22 Marauders and not the .25 Marauder.
    Is this a correct assessment on my part or did Crosman merely forget to include the .25 Marauder?

    1. Jock Elliott says:


      Steve tells me the HDD works with all MRod calibers.

  2. C Peterson says:

    You and Ted do a wonderful job of informing us to good modifications to our Air rifles. Is this mod. helpful on other Crosman products such as their nitro piston models, and are there benifits or just on the precharged. I plan on purchasing this for my Discovery model.

    1. Jock Elliott says:

      C Peterson,

      An HDD provides no benefit to a spring-piston or nitro-piston powerplant.

  3. Marcelle Nel says:

    Thank you for this great invention Steve, and Jock for hosting it on this blog. I do not actually own a Marauder yet, I’m going to import it from AoA some time soon. Just battling with all the import permits and police clearence (to prove I’m not a criminal trying to import a weapon). Anyhow, the HDD is definitely coming as well. Oh and I’m in South Africa 🙂

    Thanks again for everything!

    1. Jock Elliott says:


      Thanks for the kind words!

  4. lee wildasin says:

    i installed the hdd on my .25 maraurder,now the bolt wont catch so i cant cock the worked at first but i had to keep pulling back on yhe bolt till it would finally catch,after 6 shots it wont catch and cock.what is wrong?

  5. jacob says:

    Thanks for this HDD it is awesome what it does with the rifle.

  6. Geoff says:

    can this be done on the airarms s410

    1. Jock Elliott says:


      It probably can be done, but each hammer debounce device is airgun-specific. I don’t know if anyone is making an HDD for the AirArms 410.

  7. stephen ragsdale says:

    I purchased a synthetic stock marauder and noticed several changes made to the receiver on the on the new models.Will the HDD mod work the same on the new marauders?

    1. Jock Elliott says:

      The current HDD fits only the woodstocked Marauders. A revised HDD design is in development.

  8. says:

    want to buy HDD

    1. Jock Elliott says:


      Contact the good folks at

  9. Dustin says:

    I’m checking to see how the HDD is coming for the synthetic marauder is going. I just bought a marauder and at the time only the synthetic was available. the noise of the hammer is a little annoying but I could live with it. but I would like to make it less of a air hog if I could. I hope to hear from you soon on this. thanks for your time.

    1. Jock Elliott says:


      I am told by Steve, the creator of the HDD, that “We have a new prototype HDD for the SynRod undergoing testing right now. “

      1. Dustin says:

        thank you for the response and I hope to see it soon.

  10. mark says:

    Do I need the HDD on my new M-rod .177 synthetic?

    1. Jock Elliott says:


      The HDD will give you a flatter and more consistent shot curve.

  11. Dean Sensui says:

    I noticed that the most recent version of the .25 Marauder has a “de-pinger” installed.

    Does this perform the same function as the HDD?

    1. Jock Elliott says:


      According to Steve, the designer of the HDD, “A “de-pinger” is an acoustic baffle placed inside the air tube to lessen the bell-like tone (“ping”) sound created by resonance of the high density air column in the tube when a shot is fired and that some shooters find annoying. Unlike the AoA HDDs (Hammer Debounce Devices), a de-pinger does nothing to make the gun more efficient, increase shot count without reducing power, or reduce muzzle blast. It just reduces ping.”

  12. STEVE says:


    1. Jock Elliott says:



Leave a Reply

3 + two =