Hi Folks,
I’ve been working for a while on solving the slow first shot issue in the FX DRS. I’ve done various tests and tried different types of O-rings and greases.
Finally, after working on it for a long time, I can say that I’ve pretty much solved the problem, as long as the DRS is properly tuned and you have no regulator creep.
Why is the first shot slow?
The slow first shot happens because an O-ring around the valve pin tends to stick. This usually becomes noticeable after an hour, or sometimes even after 24 hours. The first slow shot is typically about 30–40 FPS slower or even more.
Why solve this?
The first shot is especially important for hunters. They need to be able to rely on that first shot. I’m not allowed to hunt with PCPs in my country, but even so, I want the first shot to be consistent and accurate for benchrest shooting.
Valvepin
I polished the valve pin until it looked like a mirror on both ends, without removing any material.
Which O-ring is causing the problem?
O-ring #10 → 2.9 x 1.78 mm PUR 90 is the O-ring that tends to cause the issue. Look at the O-ring that came out of my DRS, not good.
Which O-rings have I tested?
I tried a 2.9 x 1.78 mm Viton (FKM) 80 Shore A O-ring. This one performed better then PUR90 but still started to stick after about half an hour.
Then I tested a 2.9 x 1.78 mm NBR (Nitrile) 90 Shore A O-ring. This one seemed to perform the best, provided the right grease was used.
Use the NBR 90 O-ring.
Which greases have I tested?
I tried Krytox GPL 205 G0. Initially, it worked very well, but after 24 hours, it started to stick a bit and lost the trust in it.
Then I tested Huma Airgun Lube Silicone Grease. Important: don't use too much! Apply it very lightly,just enough to leave a thin film is sufficient.
I tested both of these lubricants on the two different O-rings. The best result was with the Huma Airgun Lube Silicone Grease, make sure to use that one.
Final Conclusion:
After 24 hours, the first shot remains consistent and accurate. Keep in mind that temperature can affect pellet velocity. Here in Belgium, the weather has been quite warm in the past few days, which may influence results slightly. The first image shows the shots taken in the morning. The second image shows the shots taken one day later, slightly after noon, so nearly 28 hours in total between both sessions.
Enjoy!
I’ve been working for a while on solving the slow first shot issue in the FX DRS. I’ve done various tests and tried different types of O-rings and greases.
Finally, after working on it for a long time, I can say that I’ve pretty much solved the problem, as long as the DRS is properly tuned and you have no regulator creep.
Why is the first shot slow?
The slow first shot happens because an O-ring around the valve pin tends to stick. This usually becomes noticeable after an hour, or sometimes even after 24 hours. The first slow shot is typically about 30–40 FPS slower or even more.
Why solve this?
The first shot is especially important for hunters. They need to be able to rely on that first shot. I’m not allowed to hunt with PCPs in my country, but even so, I want the first shot to be consistent and accurate for benchrest shooting.
Valvepin
I polished the valve pin until it looked like a mirror on both ends, without removing any material.
Which O-ring is causing the problem?
O-ring #10 → 2.9 x 1.78 mm PUR 90 is the O-ring that tends to cause the issue. Look at the O-ring that came out of my DRS, not good.
Which O-rings have I tested?
I tried a 2.9 x 1.78 mm Viton (FKM) 80 Shore A O-ring. This one performed better then PUR90 but still started to stick after about half an hour.
Then I tested a 2.9 x 1.78 mm NBR (Nitrile) 90 Shore A O-ring. This one seemed to perform the best, provided the right grease was used.
Use the NBR 90 O-ring.
Which greases have I tested?
I tried Krytox GPL 205 G0. Initially, it worked very well, but after 24 hours, it started to stick a bit and lost the trust in it.
Then I tested Huma Airgun Lube Silicone Grease. Important: don't use too much! Apply it very lightly,just enough to leave a thin film is sufficient.
I tested both of these lubricants on the two different O-rings. The best result was with the Huma Airgun Lube Silicone Grease, make sure to use that one.
Final Conclusion:
After 24 hours, the first shot remains consistent and accurate. Keep in mind that temperature can affect pellet velocity. Here in Belgium, the weather has been quite warm in the past few days, which may influence results slightly. The first image shows the shots taken in the morning. The second image shows the shots taken one day later, slightly after noon, so nearly 28 hours in total between both sessions.
Enjoy!
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