Air Venturi Air Venturi AvengeX FPS Gets Slower

[Konohika]

This is my first post here. I have an Avenge X. Donny FL suppressor. I usually shoot 50 shots at a time over a Chrono. As I shoot those 50 shots, the FPS continues to decrease over those 50 shots. I am thinking I have something wrong with my regulator, but I know just enough to be dangerous. So I thought I would ask the folks with experience.

"Air Rifle Pellet, 18.1 gr"
#,SPEED (FPS),Δ AVG (FPS),KE (FT-LB),POWER FACTOR (KGR⋅FT/S),TIME,SHOT NOTES

1, 899.4, 35.9, 32.5, 16.3, 12:01:13,
2, 886.3, 22.7, 31.6, 16.0, 12:01:24,
3, 883.2, 19.6, 31.3, 16.0, 12:01:33,
4, 882.2, 18.7, 31.3, 16.0, 12:01:42,
5, 882.5, 19.0, 31.3, 16.0, 12:01:49,
6, 883.3, 19.7, 31.3, 16.0, 12:02:00,
7, 880.6, 17.1, 31.2, 15.9, 12:02:18,
8, 874.5, 11.0, 30.7, 15.8, 12:02:24,
9, 877.5, 13.9, 30.9, 15.9, 12:02:29,
10, 877.1, 13.6, 30.9, 15.9, 12:02:39,
11, 877.2, 13.7, 30.9, 15.9, 12:02:56,
12, 872.8, 9.3, 30.6, 15.8, 12:03:05,
13, 874.2, 10.6, 30.7, 15.8, 12:03:16,
14, 873.6, 10.1, 30.7, 15.8, 12:03:24,
15, 873.2, 9.7, 30.6, 15.8, 12:03:31,
16, 870.6, 7.1, 30.5, 15.8, 12:03:38,
17, 873.8, 10.3, 30.7, 15.8, 12:03:46,
18, 872.4, 8.8, 30.6, 15.8, 12:03:54,
19, 869.6, 6.1, 30.4, 15.7, 12:04:02,
20, 868.2, 4.6, 30.3, 15.7, 12:04:09,
21, 876.9, 13.4, 30.9, 15.9, 12:04:34,
22, 871.1, 7.5, 30.5, 15.8, 12:04:42,
23, 871.0, 7.5, 30.5, 15.8, 12:04:50,
24, 866.4, 2.9, 30.2, 15.7, 12:04:57,
25, 869.5, 6.0, 30.4, 15.7, 12:05:08,
26, 864.3, 0.8, 30.0, 15.6, 12:05:14,
27, 864.3, 0.7, 30.0, 15.6, 12:05:22,
28, 866.5, 3.0, 30.2, 15.7, 12:05:28,
29, 865.5, 2.0, 30.1, 15.7, 12:05:35,
30, 867.1, 3.5, 30.2, 15.7, 12:05:46,
31, 865.6, 2.1, 30.1, 15.7, 12:06:06,
32, 864.8, 1.3, 30.1, 15.7, 12:06:18,
33, 859.1, -4.4, 29.7, 15.6, 12:06:24,
34, 864.4, 0.8, 30.0, 15.6, 12:06:50,
35, 865.7, 2.2, 30.1, 15.7, 12:07:07,
36, 866.2, 2.7, 30.2, 15.7, 12:07:14,
37, 857.8, -5.7, 29.6, 15.5, 12:07:22,
38, 860.7, -2.8, 29.8, 15.6, 12:07:40,
39, 854.2, -9.4, 29.3, 15.5, 12:07:46,
40, 856.2, -7.3, 29.5, 15.5, 12:07:52,
41, 874.9, 11.3, 30.8, 15.8, 12:11:31,
42, 859.7, -3.8, 29.7, 15.6, 12:11:42,
43, 586.8, -276.7, 13.8, 10.6, 12:11:50,
44, 857.6, -5.9, 29.6, 15.5, 12:11:59,
45, 852.5, -11.0, 29.2, 15.4, 12:12:06,
46, 856.5, -7.0, 29.5, 15.5, 12:12:14,
47, 856.8, -6.7, 29.5, 15.5, 12:12:20,
48, 855.0, -8.6, 29.4, 15.5, 12:12:30,

AVERAGE SPEED,863.5,,,,,
STD DEV,41.5,,,,,
SPREAD,312.6,,,,,
AVERAGE POWER FACTOR,15.6,,,,,
PROJECTILE WEIGHT(GRAINS),18.1,,,,,
AVG KINETIC ENERGY,30.0,,,,,


SESSION NOTE,"",,,,,





-,,,,,,





DATE, "July 2, 2025 at 12:00",,,,,


All shots included in the calculations,,,,,

 

[Freddy J]

Looks like you loaded two pellets on shot 43. easy to do.

 

[nervoustrig]

This effect is usually indicative of having a little too much hammer spring tension. In other words, the gun is operating up on the velocity plateau and the velocity is highest when the reservoir pressure is highest, and gradually falls with the reservoir pressure.

If you haven't already, try adjusting it to the velocity knee and check the result.

Adjusting a regulated PCP

Potentially contributing to it is the condition of the regulator's valve seat. If simply adjusting the hammer spring tension does not improve things satisfactorily, see this topic:

Regulator creep, contributing factors, and how to deal with it

 

[Raider03]

This effect is usually indicative of having a little too much hammer spring tension. In other words, the gun is operating up on the velocity plateau and the velocity is highest when the reservoir pressure is highest, and gradually falls with the reservoir pressure.

If you haven't already, try adjusting it to the velocity knee and check the result.

Adjusting a regulated PCP

Potentially contributing to it is the condition of the regulator's valve seat. If simply adjusting the hammer spring tension does not improve things satisfactorily, see this topic:

Regulator creep, contributing factors, and how to deal with it

Does that also apply if the airgun is regulated?

 

[nervoustrig]

Yes, both aspects are specifically related to regulated airguns.

 

[Booder98]

I won't put the link, because it's on another website. But Google 'rsterne tuning' and it will take you to his writings on tuning regulated airguns.

What nervoustrig is saying and what your data is showing is this, in one of rsterne's graphs. The blue line is where the hammer is turned up high.