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Air Venturi Avenger Bullpup precharged rifle: Part 4

Avenger bullpup
Air Venturi Avenger Bullpup.

Part 1
Part 2
Part 3

This report covers:

  • Adjustments
  • Today’s test
  • Adjustments are very accurate
  • Shot count
  • Discussion
  • Summary

Today we take a second look at the velocity of the .25-caliber Air Venturi Avenger Bullpup that I’m testing. Remember, this one is the .25 — not the .177 that 45Bravo told us about last week. We haven’t seen this one since January 12.

After the stunning success of yesterday’s accuracy test with the TX200 Mark III tuned with Tony Leach’s 22mm piston kit I dreaded today’s report. In fact adjustability is what makes all these modern PCPs difficult to test. I could spend a lot of time tweaking this and that and always wonder whether I hit the sweet spot. And, despite what you hear on YouTube, the sweet spot is not always in the same place from rifle to rifle. In other words — dialing an airgun in by somebody else’s directions doesn’t always work — even when I am the one giving them!


The Avenger Bullpup has a user-adjustable regulator and also a user-adjustable hammer spring. Which one do I tweak first and how much? Well, there are infinite answers to that question, so I picked a place and started there.

In Part 2 I tested the rifle as it came from the factory. That was with the regulator set at 2900 psi. I got 30 shots that averaged 788 f.p.s., which with the test pellets produces 46.82 foot-pounds. The high was 799 f.p.s. and the low was 779 f.p.s.

In Part 3 I adjusted the Avenger regulator as low as it would go, which on the onboard gauge read 1800 psi. I left the hammer spring alone. And what were the results? I shot JSB Exact King Heavy pellets, which in .25 caliber weigh 33.95-grains. My fastest shot with this setting was 769 f.p.s. I shot a long string of shot and the slowest one was on shot 52 where the pellet went out at 710 f.p.s. That’s a total spread of 59 f.p.s.

With the long string in this test you can pick the start and stop points you want. And the average changes as you do, but I called it 732 f.p.s. and that’s good for an energy of 40.4 foot-pounds.

Today’s test

Today I set the reg pressure at 2600 psi. You can’t lower the reg pressure with air in the reservoir, but you can raise it. So I filled to 4350 psi and slowly adjusted the reg pressure screw until the gauge showed 2600 psi. Do this slowly because the pressure take a little time to change.

Avenger bullpup reg gauge
After adjustment the regulator gauge read 2600 psi.

Now I adjusted the hammer spring to have more tension. Every three shots I adjusted the spring a half-turn tighter, starting from where it was set from the factory.

1…………….786 4350 psi remaining

Half turn up

Half turn up (one full turn from the start)

Half turn up (1.5 turns from the start)
12……………807 3100 psi remaining

At this point I could see that the rifle was using air rapidly. And the power increases were not very large. So I went back down to the point where the velocity was in the 790s. That was one full turn down.

One turn down (a half turn up from the start)
15……………791 3000 psi remaining

Adjustments are very accurate

Notice that when I adjusted down a whole turn I went back to where I had been two half-turns upward previously. Those numbers were 794, 795 and 790 and now going back to the same setting the numbers are 792, 789 and 791 f.p.s. So the Avenger Bullpup power adjustment is consistent.

Shot count

At this point I left the adjustments alone and just shot the rifle over and over. I watched the reservoir pressure and the regulator pressure which still read 2600 psi as of shot 15.

18…………….789 2950 psi remaining
21…………….790 2800 psi remaining
24…………….784 2650 psi remaining. Reg says 2400 psi

After shot 24 I noted that the regulator pressure gauge now read 2400 psi.

27…………….793 2500 psi remaining. Reg says 2400 psi.
30…………….786 2400 psi remaining. Reg says 2200 psi.

After shot 30 I noted that the reg pressure gauge dropped to 2200 psi. Shot number 31 was telling.

31…………….778 Off the regulator

The rifle has fallen off the regulator at shot 31. Were I to continue to shoot. the velocity would drop in a linear fashion.

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If I had left the hammer spring at a half turn up for the entire test there might have been one or even two more shots before the rifle fell off the regulator. 

If we take shot 30 as the final shot in this string and if we disregard the shots fired at a lower or higher hammer spring tension (shots 1-3 and 7-12), the spread goes from a low of 784 to a high of 795, a difference of 11 f.p.s. Let’s call 790 f.p.s. the average. At that speed this pellet produces 47.06 foot-pounds at the muzzle. That’s good enough for me.

It does seem that the .25-caliber pellet does use more air. Thirty good shots on a fill seems reasonable at the power level we are getting, and I now know how many shots I have before needing to refill during accuracy testing.


What we have learned is that the Avenger in .25 caliber needs its regulator pressure set higher, not lower. If that’s done it gets a good number of shots on a fill.

We have also learned that the regulator and the hammer spring tension both adjust in fine increments and that they return to the same place when adjusted back.

Next will be accuracy testing of this rifle.

31 thoughts on “Air Venturi Avenger Bullpup precharged rifle: Part 4”

  1. If the cocking lever had been up with the trigger, I might have been tempted. Well, I cannot say that either. As nice as the Avenger platform is, it just does not grab me. The Maximus does. Mine needs a regulator. I think they went a little too far with the Fortitude. What do I know?

        • Sorry RR,

          That was quite a while ago and don’t remember what I set the reg to but I did reduce it a bit from the factory setting.

          I read a good suggestion (somewhere) to attach a tether to the reg so you can easily retrieve it from the bottom of the reservoir for adjustments (did that).

          The reg reduces the volume of the reservoir a bit but also allows for a higher fill pressure so the shot count is still pretty good.

          All in all I like the Maximus, it’s light weight and I don’t worry too much about the plastic stock. I use it mostly as a pesting rifle that I drag around with me when I’m out working in the bush. It’s great for doing a bit of plinking when I take a break.


          • Hank,

            Thanks anyway. The idea of the tether is a good thing to keep in mind. I am guessing that you pulled the gauge block out?

            I am seriously considering increasing the size of the plenum for the regulator. I have installed an adjustable hammer spring on mine to allow fine tuning.

            I really need to find a machine shop close to me. I have a couple of mods I would like to do that require some lathe work.

        • RR,

          There was a couple of options for the gauge. I left the block in, it just reads the reg setting and only moves when the reservoir pressure drops below the reg set point. I considered removing it to maximize my shot count.

          I did look up a hammer spring adjuster/de-bouncer but have misplaced my round-tuit. That’s another project somewhere on the list. Do you have a link to the one you made that you could share?

          Hear you about making parts. I grew up with a complete machine shop in the basement (had to stand on a foot-stool to use the lathe LOL!) and missed that when I moved away. I’ve managed to cobble together a pretty decent wood/metal shop over the years. Dad bought me one of those combination lathe/milling machines a few years ago and it sees a lot of use. It’s not a high-precision machine but it’s great for what I need.

          IIRC, the HuMa plenum is just a piece of pipe so it sould be easy to try different volumes. The stock size seems to be OK, I’d be curious to hear what you discover about it.

          Maybe you could write a guest blog about your experiences with the Maximus.

    • RR, A lot of people say that about the Avenger bull pup Side lever.
      Even I said that before I bought one.

      But a lot of mainstream bullpups have the same configuration, FXdreamline bullpup, at $1029 more than the avenger
      The Benjamin Akela, an unregulated bullpup, and it cost $229 more than the avenger.
      And many others.

      I do like the stocks on those rifles, but I wouldn’t trade the accuracy and feature set the avenger offers just for a better looking stock.

      I now have about 500 pellets through mine, and while I would like to have a forward cocking lever, it’s not a deal breaker.


      • Ian,

        For me, the lever location is a deal breaker. I have shot a few ‘pups with the lever at my shoulder and just do not care for such. I have been shooting for over sixty years with the charging handle located above my right hand. I do not need to learn to be a contortionist now. 😉

    • Yogi,

      FIDDLY as if! But not an unexpected Yogi reaction…LOL!
      “PCPs are boringly accurate.”
      I thought ONLY accurate airguns were interesting?
      Why bother with the 98% of spring piston airguns that are inaccurate?

      Wisdom of those that have seen the POWER OF THE DARKSIDE.


    • Yogi,

      You can tune a PCP for power, economy or somewhere in between. I tune for best accuracy.

      Every airgun, regardless of power plant, has a (harmonic) sweet spot. With springers we search for a golden pellet, with PCPs there is the option of tuning to the pellet of choice.

      With PCPs, there’s an optimum balance between the pressure (regulator), and valve (hammer spring ) that needs to be found for a particular pellet and velocity. It’s not difficult to find, takes me about 5 minutes and 10-20 pellets to find the “ball park” setting for a velocity.

      My usual routine for a new pellet is to guesstimate the reg pressure setting, test at various velocities for group size and ES. Once I have identified a good (harmonic) velocity I’ll tweak the regulator/ hammer spring for best air consumption (and lowest noise) at that velocity then fine tune the hammer spring for best group size.

      With tuning, you are looking for the optimum spot on the power curve; the regulator sets the amplitude of the curve and the hammer spring is balanced to that power level.

      Tuning a PCP sounds more complicated than it is …it’s kinda like tuning a carburetor on an engine. It’s easy once you have done it a couple of times.

      Know that you are a springer-guy, I’m just trying to shed a bit of light on the dark side for you. 🙂


  2. B.B.,

    Given all the ways you noted that folks choose to “brew” their DarkSide coffee I believe your choice and order of steps was spot on.
    First the usual statement: without using a reliable CHRONOGRAPH trying to do this is like a dog barking up a tree.
    If some reader is wondering why set the regulator output first on the Avenger since it still has a hammer strike valve that valve still works just like an unregulated PCP’s powerplant. The benefit of the regulator is to deliver the same input pressure for each shot every time instead of the valve needing to deal with an ever decreasing input pressure on every subsequent shot. That may not seem like much of a difference but it allows the tune to be done for power (almost maximum; unregulated PCPs can get more absolute KE power) and efficiency (shot count) at stable Muzzle Velocity or something in between.

    Watch out for the folks who, unlike B.B., tell you to just set it up like their’s and that you won’t need a CHRONOGRAPH! You will need one as soon as you change pellets and/or pellet weight.


  3. Well it seems that with the regulator set to 1.8K output the spread is like an unregulated gun, but makes nearly the same velocity as when the regulator is set to a much higher output.
    The transfer port is the issue for the low regulated output readings IMHO. I think the gun is set up with a big port. The Marauder rifle has one of those, but not the externally adjustable reg. It would be nice to have a set of sized ports, cheaper than an FX too!

    • 1stblue,

      Interesting that you bring up sized transfer ports. Seems that most PCPs have fixed ports that the manufacturer has determined are best size.

      Only two of my PCPs feature port selection (Royal and Crown) and I’ve always viewed them as an adjustment made to compliment the tune (max for high power tune, min for low power tune, etc.) and set and forget them.

      Guess that a max-tuned rifle could benefit from minimum TP selection for plinking at lower power but it wouldn’t be efficient. I think changing the transfer port size seriously messes with the airflow (and the tune) which will affect accuracy.

      I prefer to use one setting rather than having too many variables. For that reason I’ve viewed multi-position transfer points as being a bit of a gimmick. Don’t know, never used them – they might be a great feature.

      Maybe someone could chime in on that.


      • See, without a chrono, how would I even know! Besides, hollowponts are a gimmick. They only work at very specific conditions. I had a 16v GTI but the 8v had much better low end. Port velocity. The Marauder ‘s transfer adjustment is for super precise tuning on top of the basic overall tune hammer spring and throw adjustments. plus you can just use a another port size. And the poppet spring. So, I agree, simpler has a good side to it.
        And with a regulator you can use a lighter hammer, So The Avenger should get allot more shots with the lower power tune, and a nice tight spread, at the cost of 4barrel, top end power. Oh wait, it’s sandals, spurs, buggy whips, carburetta’s, F.I., we’re up to F.I so far.

  4. BB,

    I was reading some of the older blogs and after reading the one about the Texan, I was curious about what you decided—upgrade it or leave it in its great shooting state? Also did you get to test it out at 100 yards?

    A related question; have you tried Nielsen bullets in the Texan? Or any other airgun you’ve used/tested?


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