Let’s Tune The Air Venturi Avenger – Part One
As we already know, the manufacturer is very keen for us to tune the AirVenturi Avenger air rifle. So, in this second part of HAM’s Avenger review, we’ll take the first steps towards tuning it.
Before starting the tune, we need a Chronograph. If you don’t have one, buy one. It’s an essential piece of equipment!
But what tune to create? The plan for this multi-part HAM review is to create two tunes for this .22 caliber Avenger:
One is a “maximum power” tune based on filling the HPA tube to its maximum 4350 PSI (300 Bar). This will work for anyone with an HPA compressor, but probably not for others. We’ll try this first.
The second is a tune that gives the best combination of shot count and power with a fill pressure of 3,000 PSI (207 Bar). This will be for the rest of us, who are filling from a hand pump or tank.
Establish A Baseline – Pressure
Before starting to tune the Air Venturi Avenger, it makes a ton of sense to understand how the gun performs in “as received” condition from the factory. Otherwise, how do we know if we have made any improvement with the tune?
So I filled it up with 4350 PSI of High Pressure Air. This was measured based on the pressure gauge of HAM’s Omega Super Charger compressor. This is a large gauge and has given very accurate pressures on test.
Why is this important? Well, we have two pressure gauges on the Avenger – one for fill pressure, the other for regulator pressure.
It’s important to appreciate that these tiny pressure gauges will have a degree of inaccuracy. If they are accurate to better than +/- 10%, that would be pretty good!
So take the pressures on these gauges as an approximation of the pressures in the gun. They are very unlikely to be 100% accurate.
Please note that this is NOT a slam on the Avenger. This is true for any airgun pressure gauge, especially ones fitted to value-priced PCPs. Any gauge of any type will have a tolerance range and small, cheap gauges are likely to be less accurate than big, expensive ones.
Here’s how the fill pressure gauge on this Avenger reads…
Clearly it’s reading 4,000 PSI for the fill reading 4,350 on the compressor gauge. That’s within reasonable tolerance for a gauge of this type.
And while we’re talking pressure gauges, note this really good feature of the Avenger’s pressure gauges. Not only do they have a green section on the gauge plate to indicate acceptable pressures, but the gauges on either side of the gun are different!
The regulator pressure gauge (below) has a green section running from 1,160 to 2,900 PSI, which is the regulator pressure setting range.
As you can see, the regulator gauge shows 2,900 PSI. So the regulator was set to the maximum set pressure – or very near it – at the factory.
Establish a Baseline – Muzzle Velocity
Having filled the Avenger with HPA, the next step was to shoot it in factory configuration. We chose to use 14.66 Grain H&N Field Target Trophy pellets as these are popular pellets of average weight with excellent manufacturing consistency.
Here’s what we found when shooting over a Chronograph…
As we can see, the Muzzle Velocity started-out around 925 FPS. It then increased steadily to about 950 FPS by shot 58. That’s in the 28 – 29 Ft/Lbs range for each shot. Pretty good!
After this, the regulator set pressure was reached and the Muzzle Velocity rose by another 25 FPS before declining.
Regular HAM readers will probably not be surprised by this graph. Bob Sterne showed just such an example in his article on “Tuning Regulated PCPs“.
Here it is below, with the appropriate line indicated. Note that Bob’s graph was based on theoretical, rather than actual data. That’s why it looks a lot cleaner than my practical results!
We’ll aim to flatten-out this shot curve by using the hammer spring tension adjuster – as indicated in the Avenger owner’s guide.
Note that this is the result when shooting with 14.66 Grain pellets. It’s likely to be different – possibly very different – when shooting pellets of a different weight.
So the final element of our efforts to tune the Air Venturi Avenger will be to select an appropriate pellet to match the regulator and hammer spring settings.
Now We’re Ready To Start
So now we understand how our Air Venturi Avenger performs in factory condition. We also have a feel for the accuracy of the gauges fitted to the gun.
Armed with this information, we can start our first tune. Check back for progress in the near future!
Here’s the Full Power tune.