N/A 😳 What's wrong with my gun? — Look at this shot string!

[JungleShooter]

What's wrong with my gun? — Look at this shot string!​

● Gun: RTI Prophet 2 Compact Performance .25cal
● Pellet: .25cal — JSB Dome 25.39
● Balanced valve️
● HST: About 1/4 turn further in than the setting where velocity drops off rapidly.


Start conditions:
▪ AIR pressure in 240cc bottle 290bar
▪ REGulator 145bar


Observations:
The velocity spread of nearby shots is very small (good!).

The first two shots are extremely low (the gun sat for 5 days). ➧ Horror for hunting!

After 25 shots, the regulator pressure gauge shows a decline of 10 bar.
And the MV shows a decline by about 20fps.
This decline continues.
➧ Very ungood.



Shot String:
The worrysome numbers are in bold.

——AIR 290 | REG 145
637fps
729
967
965
971
——AIR 275 | REG 140
974
970
973
974
973
——AIR 250 | REG 140
967
966
970
970
963
——AIR 235 | REG 140
<EDIT: I'm so sorry, I failed to enter the following 5 shots, now corrected! Thanks nervoustrig!>
962
963
964
963
959
——AIR 220 | REG 137
954
951
954
955
952
——AIR 195 | REG 135
953
950
944
949
953
——AIR 180 | REG 130
947
944
941
945
946
——AIR 160 | REG 130
944
940
943
939
949
——AIR 142 | REG 128
938
943
944
943
942
——AIR 130 | REG 128
938
937
931
934
923
——AIR 120 | REG 121
925
916
911
904
894
——AIR 113 | REG 113



I appreciate your comments and suggestions.
THANKS!

Matthias

 

[L.Leon]

After the first five shots all the rest are below the 145 BAR regulator set point. Your regulator is descending along with your shot strings. Throwing out those first two shots. You’re showing a 23 shot string with an ES of 21, which isn’t bad. But a descending regulator set point…? Hope @nervoustrig will chime in, he is very knowledgeable in these matters.

After the first five shots your reg.dropped 5 BAR

After 20 shots another 5 BAR

After 25 shots another 5 BAR

So a 15 BAR drop in the regulation? I thought regulators going below their set point could only happen if the supply side was below said set point? Am subscribing to this thread.

P.S.: Maybe lower the reg set point, could be it need not be set that high for your gun? You seem to be getting good consistent numbers at the 135 BAR shot strings that you show.

 

[weevil]

What reg pressure was used to set the HST? Obviously your reg follows the tank pressure to some extent, as many do. Tuning the HST at median tank/reg pressure can mitigate the effect. It’s asking a lot of a reg to operate between near 300 and 130bar. As for the slow first shots, that sounds like some balanced valve hijinks.

 

[JungleShooter]

The gun has a balanced valve.
My first experience with this....

The HST was about 1/4 turn *in* after the point where the velocity drops off.

Matthias

 

[weevil]

The gun has a balanced valve.
My first experience with this....

The HST was about 1/4 turn *in* after the point where the velocity drops off.

Matthias

If reg pressure varies with tank pressure then so will the optimal HST setting. In that case, setting the HST at the median tank pressure (210 bar) should provide the best buffer against variation. Alternatively, you can take a suck it and see approach, running strings at slightly higher and lower HST settings and honing in on the most stable setting.

 

[nervoustrig]

My first impressions track pretty well with weevil's. But there's one thing that really jumps out at me, and that is the rate of air consumption is wildly inconsistent.

In the portion pasted below, the first 5 shots drop the reservoir by 40 bar while the subsequent 5 shots drop it by only 15 bar. That makes absolutely no sense unless the valve is borderline sticking open at times and dumping a tremendous amount of air, and other times sips air. A discrepancy this large should be something you can hear in the muzzle report. Can you comment?

——AIR 235 | REG 140
954
951
954
955
952
——AIR 195 | REG 135 <- reservoir dropped 40 bar
953
950
944
949
953
——AIR 180 | REG 130 <- reservoir dropped only 15 bar

Otherwise the character of the gradually descending string that tracks with the regulator's descending pressure suggests the hammer strike is set a little too strongly.

 

[L.Leon]

My first impressions track pretty well with weevil's. But there's one thing that really jumps out at me, and that is that the rate of air consumption is wildly inconsistent.

In the portion pasted below, the first 5 shots drop the reservoir by 40 bar while the subsequent 5 shots drop it by only 15 bar. That makes absolutely no sense unless the valve is borderline sticking open at times and dumping a tremendous amount of air, and other times sips air. A discrepancy this large should be something you can hear in the muzzle report. Can you comment?

——AIR 235 | REG 140
954
951
954
955
952
——AIR 195 | REG 135 <- reservoir dropped 40 bar
953
950
944
949
953
——AIR 180 | REG 130 <- reservoir dropped only 15 bar

Otherwise the character of the gradually descending string that tracks with the regulator's descending pressure suggests the hammer strike is set a little too strongly.

I suspected the HS was set to strong. But a question for you… A regulator that descends with the shot string doesn’t seem right. For example the regulator on my Pathfinder stays at 150 BAR and only goes below that when there’s not enough HPA in the bottle. I thought that was where the term “falling off the regulator” came from, not enough HPA from the supply side to keep the set point of the reg.

 

[nervoustrig]

But a question for you… A regulator that descends with the shot string doesn’t seem right.

Yeah, a decline from 145 bar down to 130 bar seems like a lot, a change of 10%. It may be that the initial 145 reading was the product of creep and the actual amount is more like 140 down to 130, or a change of 7%. That's not great but as weevil mentioned, it's being asked to do a lot to cover an input : output ratio of well over 2:1 (from 290 bar down to 130 bar).

This behavior is termed input regulation, and all regulators will exhibit it to some extent but of course some are worse than others. For example, those designed for fast recovery tend to be more susceptible. The condition of the valve seat will also influence it to some extent, meaning it will change over the service life of the regulator.

Anyway the gun's sensitivity to this gradual pressure decline is likely exacerbated by the balanced valve. A conventional knock-open valve will usually handle a 7 - 10% pressure change no problem, just as a decent unregulated PCP will hold a stable velocity over a wide pressure range in and around the top of its bell curve.

 

[Vetmx]

My P2 does the same thing. I commented about it in a Prophet topic. A couple things though. I almost never go near my regs set point before I refill my guns so I don’t know if my drop is as bad as yours. It also seems like my gun doesn’t do it as noticeably as before now that I have a lot of shots through it. When my gun had too much hammer spring tension according to us taking other peoples word for it on how to tune an assisted valve prophet, I never had a slow first shot. Now I have one slow one, then it’s normal. Lastly, a descending shot string with the type of valve we have is a reg issue. Ironically my Priest ll exhibited the same behavior without a balance valve and I had a chat with Nervoustrig about it. It was the reg. And I had a Huma on it.

 

[Vetmx]

I forgot to add. I have quite a few 300b guns. I never fill them to 300b. That’s just asking too much out of those tiny regs seat.

 

[L.Leon]

Yeah, a decline from 145 bar down to 130 bar seems like a lot, a change of 10%. It may be that the initial 145 reading was the product of creep and the actual amount is more like 140 down to 130, or a change of 7%. That's not great but as weevil mentioned, it's being asked to do a lot to cover an input : output ratio of well over 2:1 (from 290 bar down to 130 bar).

This behavior is termed input regulation, and all regulators will exhibit it to some extent but of course some are worse than others. For example, those designed for fast recovery tend to be more susceptible. The condition of the valve seat will also influence it to some extent, meaning it will change over the service life of the regulator.

Anyway the gun's sensitivity to this gradual pressure decline is likely exacerbated by the balanced valve. A conventional knock-open valve will usually handle a 7 - 10% pressure change no problem, just as a decent unregulated PCP will hold a stable velocity over a wide pressure range in and around the top of its bell curve.

I initially, also thought “creep” but @JungleShooter stated it was his regulator set point. But agree as to it likely being creep from a 140 BAR set point. Thank you for responding.

 

[JungleShooter]

Thanks for all your helpful comments!!


First of all, I'm so sorry for a data entry mistake — Jason of course caught it....
➧ The "inconsistent air consumption of 40bar per 5 shots" — does actually not exist : I messed up, and simply skipped to enter 5 shots. (The OP is now corrected — showing the consumption to be fairly even.)


You dislike the decreasing REG pressure as much as I do.
➧ I will try another shot string with a different HST setting.
➧ And I don't need to be a Prophet nor Priest to see in my not too distant future an email to RTI requesting a replacement regulator....


Some of you suggest the HST might be set too strong.
➧ "Too strong" means the hammer spring is set "too tighly", thus making the hammer hit the valve "too hard" — am I undestanding that right?

➧ I fail to find any indications in either the manual or the Tube as in which direction I need to turn the HST to decrease the spring tension.
➧ To decrease HST I assume I need to turn the screw OUT — which means to turn it counter clockwise — right??
(Note that I am only about 1/4 turn HST away from getting a 200fps drop in MV.)


Some blame the first two very weak shots on the "high" 300bar in the bottle.
➧ Sorry, the Compact only comes with a spoonfull of HPA, so I need to carry all the air I can cram into that baby bottle of 240cc.

Some blame the weak shots on an HST set too weakly.
➧ Well, I'll mess with the HST today again.



In any case, I will report back.

Matthias

 

[orion]

Matthias, that regulator moving all over doesn't seem right. If the gun is new I recommend not filling all the way to 300 yet until the regular settles, at least this is what I do when new. Fill to 250 max and tube from there.

Tightened the screw in the back increases the HS tension. I recommend you loose it all the way to begin your tune.

This is what I think is happening, you start with 300 bar and a creep is setting your reg to a higher pressure but your regulator value is actually lower is the creep that is moving the needle, then you tune for that high pressure and when the bottle pressure decreases then your regulator is back to the original pressure with no creep and then you are out of tune.

I know the bottle is tiny. I'll send you a picture of the bottle I'm using, I got this from China and it's working really well for me, it gives me more shots, something to consider for later.

For now just fill max 250 and tune, use the gun a monitor the creep it should get better over time is it doesn't then reach out RTI because the regulators are working really good nowadays

 

[weevil]

Thanks for all your helpful comments!!


First of all, I'm so sorry for a data entry mistake — Jason of course caught it....
➧ The "inconsistent air consumption of 40bar per 5 shots" — does actually not exist : I messed up, and simply skipped to enter 5 shots. (The OP is now corrected — showing the consumption to be fairly even.)


You dislike the decreasing REG pressure as much as I do.
➧ I will try another shot string with a different HST setting.
➧ And I don't need to be a Prophet nor Priest to see in my not too distant future an email to RTI requesting a replacement regulator....


Some of you suggest the HST might be set too strong.
➧ "Too strong" means the hammer spring is set "too tighly", thus making the hammer hit the valve "too hard" — am I undestanding that right?

➧ I fail to find any indications in either the manual or the Tube as in which direction I need to turn the HST to decrease the spring tension.
➧ To decrease HST I assume I need to turn the screw OUT — which means to turn it counter clockwise — right??
(Note that I am only about 1/4 turn HST away from getting a 200fps drop in MV.)


Some blame the first two very weak shots on the "high" 300bar in the bottle.
➧ Sorry, the Compact only comes with a spoonfull of HPA, so I need to carry all the air I can cram into that baby bottle of 240cc.

Some blame the weak shots on an HST set too weakly.
➧ Well, I'll mess with the HST today again.



In any case, I will report back.

Matthias

Matthias, I wouldn’t demand a new reg yet! Dry fire the gun a couple hundred times from 250-150 fills to settle it in, then tune at 210-190bar fill and see if things improve.

 

[orion]

This is the bottle I'm using

 

[JungleShooter]

Erlis and Colin,

the gun isn't new — as I usually need to buy used guns to indulge my performance cravings within the budget I have.

I will do some more testing today and report back.


And that larger bottle, Erlis, yes, I'd love to have a link to AliExpress for that....

Matthias


PS: What a great community we have. So much help, so quickly!

 

[darylm]

Swap it out with this one and never look back

https://www.airgunsofarizona.com/regulators/huma-regulator-for-rti-priest-prophet-and-prophet-ii/

 

[c_m_shooter]

First, the Regulator doesn't seem right. It should not decsend with the tank pressure until below the set point.

 

[JungleShooter]

Swap it out with this one and never look back

https://www.airgunsofarizona.com/regulators/huma-regulator-for-rti-priest-prophet-and-prophet-ii/

Thanks for throwing out that option.
It really shouldn't have to come to this... — considering this is an expensive gun to start with...!

I will keep this in mind.


However, reading from the Huma website*:
➊ I see this regulator only adjust to 170bar (vs. RTI: 200 or at least 180bar, there's conflicting info).

➋ "The maximum working pressure of this model is 250 Bar."
➔ Do I understand this correctly to mean I can only fill my air bottle to 250bar, not RTI's 300 bar...?

➌ The real killer is that this regulator is not externally adjustable, at least not unless I dump all the air every time I adjust the reg — that's what I gather from the following Huma statement:
"For testing and adjusting your regulator we recommend you our simple Testing Tool what makes it very easy to adjust your regulator without the need of emptying your pressure bottle with every adjustment."


Matthias




*Huma website:

RTI Prophet Adjustable Tuning Regulator By Huma-Air

Huma-Air adjustable pressure regulator for the RTI Prophet. Suitable for all RTI Pries models

www.huma-air.com

 

[orion]

Alsafe Hot Sale Matting Mini Pcp Paintball Gas Cylinder 0.3l 0.48l 0.58l 0.7l 4500psi 300bar Carbon Fiber Air Tanks - Buy 4500psi Cylinder For Pcp 300bar Paintball Gas Cylinder Carbon Fiber Tank For Paintball Carbon Fiber Tank 4500psi Pcp,4500psi Car

Alsafe Hot Sale Matting Mini Pcp Paintball Gas Cylinder 0.3l 0.48l 0.58l 0.7l 4500psi 300bar Carbon Fiber Air Tanks - Buy 4500psi Cylinder For Pcp 300bar Paintball Gas Cylinder Carbon Fiber Tank For Paintball Carbon Fiber Tank 4500psi Pcp,4500psi Carbon Fiber Air Tank Cylinder For Pcp 4500psi...

www.alibaba.com

The 0.3L bottle

You can just order 1 bottle from them