Air Venturi Avenge X .177 readings - are these normal?

[Maxgasmekl]

As per my earlier posts my Avenge X has been somewhat inconsistent in its shooting behaviour. I ended up cleaning the barrel with a soft piece of cloth pullet througt the barrel from the breech side and out and also tightened every set screw down. I bought some JST Exact Heavy Diabolo 10.34 gr pellets and these were a gamechanger. For a short while. Because after a few 100 pellets the gun returned to its previous stage and became inconsistent with a lot of poi shifting. The scope is tight and level. The screws are tight. So then I bought a cheap china chrono that should be pretty acurate and these were my first readings:

JSB Exact Heavy Diabolo 10.34 gr pressure from 4000psi down to 2500 psi, reg 1800 psi and HS all the way out
942.8 942.8 951.0 959.4 955.2 955.2 955.2 951.0 951.0 942.8 938.8 934.8 934.8 942.8 942.8 942.8 938.8 938.8 946.9 938.8 915.2 911.4 911.4 900.2 915.2 907.6 900.2 900.2 911.4 903.9 919.1 911.4 907.6 911.4 911.4 907.6 911.4 900.2 907.6 911.4 889.2 892.8 885.6 875.0 864.6 892.8 900.2 896.5 889.2 892.8 915.2 915.2 915.2 903.9 907.6 900.2 903.9 907.6 907.6 900.2

There is a lot of inconsistency and as the hammerspring is turned all the way out, I dont know what to adjust other than the reg to get the fps down to a sub 900 level. I would like some advice on how i can improve/tune this. Here is a picture of my “groups” from 22 m (indoor)

Thanks

 

[Ranchibi]

By the fps numbers, either the tune is way off or your regulator needs some work or both.

 

[Maxgasmekl]

By the fps numbers, either the tune is way off or your regulator needs some work or both.

I havent done any tuning yet:/

 

[nervoustrig]

The first step for a typical regulated PCP is to dial the hammer spring tension up until the velocity no longer increases. Then back it off until the velocity falls by 3 - 5%.

If your Avenger is like mine, the hammer spring adjustment doesn't have enough range when the regulator is set below 2000psi or so. I had to shorten the hammer spring a little. Things improved considerably.

Air Venturi - Multiple Air Venturi Avengers with Regulator Creep

Hey all, I'm pretty new to airguns, and this is my first PCP. I've had it for 2 days and am noticing a weird issue. When I fill the gun to the 4200 PSI and set the regulator at 1800 PSI, as it sits the main tank pressure will drop to about 4100 PSI and the regulator pressure will climb to...

www.airgunnation.com

 

[Maxgasmekl]

The first step for a typical regulated PCP is to dial the hammer spring tension up until the velocity no longer increases. Then back it off until the velocity falls by 3 - 5%.

If your Avenger is like mine, the hammer spring adjustment doesn't have enough range when the regulator is set below 2000psi or so. I had to shorten the hammer spring a little. Things improved considerably.

Air Venturi - Multiple Air Venturi Avengers with Regulator Creep

Hey all, I'm pretty new to airguns, and this is my first PCP. I've had it for 2 days and am noticing a weird issue. When I fill the gun to the 4200 PSI and set the regulator at 1800 PSI, as it sits the main tank pressure will drop to about 4100 PSI and the regulator pressure will climb to...

www.airgunnation.com

Ok, so either I should increase the reg to 2000psi or increase hammer tension even more, although its alteady shooting way above the 900 fps range ( most of the time)

 

[nervoustrig]

You would not want to increase hammer spring tension even more…the gradual declining velocity suggests it is already too high. Also, a rough calculation of the efficiency shows it to be fairly low (1.06fpe/ci) which is another clue it is wasting air.

The options are either increase the regulator setpoint or shorten the hammer spring. Which one is better in this situation? Well if it’s grouping the 10.3gr pellets nicely, I wouldn’t recommend increasing the regulator pressure because that will likely push the velocity up to 1000fps or higher where accuracy usually diminishes. So that makes the hammer spring the better candidate. Either shorten it (e.g. remove half a coil and re-test) or replace it with a weaker or shorter one. Ideally what you want is the ability to max out the velocity just before you run out of travel on the hammer spring adjuster, and then back it off so the velocity drops to about 97% of the maximum.

So for example if it maxes out at 980fps, you would then back off to 980 * 0.97 = 950fps. When adjusted in this manner, it will produce a more consistent velocity and give you a bump in shot count, and likely improve accuracy a bit.

 

[Bramezy]

Where is the transfer port set? I was able to tune mine in 177 down to 10.3 at 900ish on low and then turn to high for 13/16gr. Turn transfer port to low and tune it there.

 

[Maxgasmekl]

You would not want to increase hammer spring tension even more…the gradual declining velocity suggests it is already too high. Also, a rough calculation of the efficiency shows it to be fairly low (1.06fpe/ci) which is another clue it is wasting air.

The options are either increase the regulator setpoint or shorten the hammer spring. Which one is better in this situation? Well if it’s grouping the 10.3gr pellets nicely, I wouldn’t recommend increasing the regulator pressure because that will likely push the velocity up to 1000fps or higher where accuracy usually diminishes. So that makes the hammer spring the better candidate. Either shorten it (e.g. remove half a coil and re-test) or replace it with a weaker or shorter one. Ideally what you want is the ability to max out the velocity just before you run out of travel on the hammer spring adjuster, and then back it off so the velocity drops to about 97% of the maximum.

So for example if it maxes out at 980fps, you would then back off to 980 * 0.97 = 950fps. When adjusted in this manner, it will produce a more consistent velocity and give you a bump in shot count, and likely improve accuracy a bit.

Ok, thank you But isnt it hard to tune that way when the fps goes up and down as the listed numbers are showing? How is it loosing air?

 

[nervoustrig]

isn’t it hard to tune that way when the fps goes up and down

I see what you’re saying…if the velocity is inconsistent, how can you expect to tune it to a particular velocity? But what happens is, when you follow the process of gradually adding hammer spring tension until the velocity maxes out, and then back off a little, what you will find is it will produce a more consistent velocity. Not 950, 950, 950, 950, but something more like 952, 948, 954, 945, 959.

That’s not to say it’s a magic wand. There could be something else causing the inconsistency but step #1 for a regulated PCP is get the hammer spring tension set in harmony with the regulated pressure. Then re-evaluate how it’s doing.

How is it loosing air?

Not losing air, wasting air. Meaning using more air per shot than it should.

Oh and Bramezy made a good point. I was thinking of the original Avenger but you have the Avenge X which a transfer port adjuster. In that case you may want to try simply increasing the reg setpoint and then see whether the hammer spring adjuster will operate in a useful manner. If the resulting velocity is too high for the 10.3gr, move the transfer port setting to Low and check.

 

[Maxgasmekl]

I see what you’re saying…if the velocity is inconsistent, how can you expect to tune it to a particular velocity? But what happens is, when you follow the process of gradually adding hammer spring tension until the velocity maxes out, and then back off a little, what you will find is it will produce a more consistent velocity. Not 950, 950, 950, 950, but something more like 952, 948, 954, 945, 959.

That’s not to say it’s a magic wand. There could be something else causing the inconsistency but step #1 for a regulated PCP is get the hammer spring tension set in harmony with the regulated pressure. Then re-evaluate how it’s doing.



Not losing air, wasting air. Meaning using more air per shot than it should.

Oh and Bramezy made a good point. I was thinking of the original Avenger but you have the Avenge X which a transfer port adjuster. In that case you may want to try simply increasing the reg setpoint and then see whether the hammer spring adjuster will operate in a useful manner. If the resulting velocity is too high for the 10.3gr, move the transfer port setting to Low and check.

Thank you for clarifying. If i move the transfer port to low as it is now - it will be in the 750 fps range. And that is a bit to low. Would you recommend trying the hammerspring adjust first and then maybe the reg adjust? It wouldnt help just to lower the reg pressure to 1600 psi to get the gun to shoot in the high 800s? What could else cause the inconsistency?