Air Venturi What might this mean - if anything?

[Aslap]

I had my Avenge X 25 out today for some testing at 50 yards. That turned out to be one of those some good; some bad stories.

When I got back home, I filled the gun up and hooked up the chrony. I was using my Apolo cheap 25 grain pellets. I wanted to see just how the regulator was performing over a full shot string. Here is what that looked like.

Number one is that the regulator seems, to me, to not be doing a very good job of regulating. Granted, the taper off is kind of small but I'd expect to see a much straighter line up to the fall off point. But that isn't the interesting thing. Look at the velocity staying relatively constant while the regulator pressure is dropping. So I then plotted the FPS/Reg P and got this.

This is showing graphically that I'm getting more velocity at lower reg pressures. I'm wondering what this means. It looks to me like if I back the hammer spring off a bit, that the tilt in this graph may be turned into a straighter line. It almost looks like at the higher pressures I'm hitting valve lock with the current hammer spring setting and as the pressure drops, the valve lock eases up so I get the same kind of velocity. Isn't that what an unregulated gun does? That stupid low SD on this data is telling me that there is an extremely strong interplay here between the pressure and the speed. Any data that plots a line like this with relatively equal excursions at the front and back end with a fairly straight connection between the two will give a very low SD.

Is there anything in this that would point to whether or not a system is in a nice state of balance in terms of pressure and valve operation? Any opinions on the performance of the regulator? I should also mention that 2 days ago with the same pellet and the same reg set point, the speed was averaging 905 FPS and I had a smaller SD on the velocity that I see here. Why this would change is unknown to me. If this sounds like the ramblings of a confused man, it should, I am a confused man at this point.

Tony

 

[nervoustrig]

The ~10 bar decline in the regulated pressure is not an impediment so don't get too hung up on that aspect. It's actually pretty good for a regulator experiencing a reservoir swing of 150 bar (300 bar fill down to a 150 bar setpoint).

Regarding the tendency for the average velocity to climb a bit as the pressure falls...to help level it off, what you would want to do to is increase hammer spring tension a smidge to overcome the partial valve lock occurring at higher pressure. That will reduce the frequency of dips in the first half of the shot string, bringing up the average velocity in that region.

 

[Aslap]

Nervous,

OK! That makes sense. I’ll give that a try tomorrow and rerun the test. Good news on the regulator then. I can put that aside.

Tony

 

[PumaCarl]

Also, I know you don't want to hear this, but, I would suggest not filling to 300bar. Yes, you can, but you get problems like you are having too. In the long run, it's not worth it, just fill to 260b tops. Life is smoother when you're not under so much pressure. Just because it is designed to handle it, that doesn't mean that is where it works the best.

 

[blackdog899]

Also, I know you don't want to hear this, but, I would suggest not filling to 300bar. Yes, you can, but you get problems like you are having too. In the long run, it's not worth it, just fill to 260b tops. Life is smoother when you're not under so much pressure. Just because it is designed to handle it, that doesn't mean that is where it works the best.

Carl, I know you’re right totally BUT there’s something in me that prevents common sense. I mean I have the 9 liter right there at my bench yet I still have to fill to the point of blowing o rings or burst discs.
I just posted filling my 9 liter and look at the gauges. I honestly think you registered with me tonight.

 

[PumaCarl]

YOLO, ... YODO too! Nah, it's not that extreme, but when the burst disc blows the first time you're standing over it, just make sure you didn't hold off going to the bathroom!

 

[Aslap]

Carl,

Also a good thing to try. Since this rifle will basically be a 25 yard backyard plinker/target shooter, the ultimate shot count on a fill doesn’t much matter to me as long as it gets more than, say, ten. I could see where lowering the fill pressure would help to even out the regulator action. Perhaps a lower fill pressure would also work to mitigate the partial valve lock situation at the start of a string?

Good suggestions and thanks for the help!

Tony

 

[Aslap]

I did a tremendous amount of testing today using the tips given here and will post results later. In the meantime, is there a minimum pressure recommended the the Avenge X regulator? That is, is there a pressure below which the regulator will perform poorly or not at all?

Tony

 

[mercado]

Try to use AEA pellets.. when I tested my gun with jsb I was very disappointed spread was to much I thought that the regulator was bad . Change to AEA and my spread go from 10 to 20+ fps to 4 to 5 .. the jsb wasn't to good.

 

[Aslap]

I started off using Carl's advice with the lower fill setting. of 250B. The reg pressure was like it was at around 155B.
Hammer spring as it was with 250B fill.

Little bump on the hammer spring by 1/8 of a turn in.

Starting yo look better I though. Another 1/8 turn in on the spring for a 1/4 turn in.

I found this interesting. A kind of different look to the tilt of the reg pressure curve. This is the best SD I have seen on the gun so far. Gave it one more 1/8 turn in for a 3/8 turn in total. Funny that the FPS dropped some.

When I saw the huge jump in FPS I was kind of surprised. I thought I had gotten things to the point where I had peaked out the HS at this reg pressure. I was wrong. I spent time giving it more hammer spring and I wound up at almost 970 FPS on the 25 grain cheapo pellets.

I figured I need to get the reg pressure down so I set it right around 130B and I worked the hammer spring until I peaked it out. The results were poor and that led to my earlier question about the lower adjustment limit on the Avenge X regulator. AT 130 bar, the FPS is clearly tracking what's happening in the tube. I have more work to do but I am in agreement with Carl that the lower fill pressure really cuts the total reg pressure deviation over a shot string.

Tony

 

[Aslap]

Mercado,

Agreed on the cheapo pellets probably giving me issues. I have a few AEA 25 grain (probably enough for a couple of runs. I'll try those. Here are a couple of shots of the AEA 25's at 50 yards yesterday. % shot groups. I was having rest issues so I also got a bunch of extremely poor groups. These three were shot one after another. The aiming dot is 0.29" diameter. I had worked them using OnTarget TDS but didn't save the statistics. The first two are around .26 CTC and that last one was something like .17 CTC.

Tony

 

[Aslap]

Also, the graph at the beginning of the thread was using the same reg set point and the same hammer spring adjustment as the first test today at a 250 bar fill pressure. At 300 bar fill, I was seeing 940 FPS. At the 250 bar setting, the average was 895. Where did the extra. 45 FPS go? Overall the reg pressures were pretty much the same over both strings.

Tony