Pellet - Variation of speed during a match ?

[Bruno Almeida]

Friends,

If the cilinder is fully charged, ~200 bar, the speed of the pellet is meant to drop after ~85 shots, or, as long as the manomether stays within the "green zone" the speed shouldnt have considerable change ?

All rifles has the same behavior ?

Thank you.

[RobStubbs]

Friends,

If the cilinder is fully charged, ~200 bar, the speed of the pellet is meant to drop after ~85 shots, or, as long as the manomether stays within the "green zone" the speed shouldnt have considerable change ?

All rifles has the same behavior ?

Thank you.

It should stay the same in a decent gun with a good regulator.

Rob.

[JeroenH]

When selecting pellets, I've noticed that my V0 increases from about 165 m/s (200 bar) to 170 m/s (pressure dropping below 100 bar).
Yes, that's right: higher pressure yields lower V0.

Some ballistic calculations show that this causes my pellets to end up 1.1 mm higher on a nearly empty cylinder compared to a full cylinder. Which is OK for me because in one match I use less than half a cylinder.

Still, this is one of the reasons that re-clicking during the match might be a good idea.

[BigAl]

There are two main types of precharged air rifle. The basic design uses a very simple knock open valve to pass the air from the cylinder to the barrel. The weight and speed of the hammer hitting the valve, and the pressure in the cylinder will regulate the velocity. If you increase the pressure above a certain point then the hammer will not be able to open the valve fully and velocity/energy will be reduced. Over a reasonable pressure range this self regulating system can be very consistent. At least for sporting rifle. All unregulated guns will vary on the optimum pressures. Often the max working pressure reccomended may be high enough to actually reduce the velocity. As the pressure reduces the velocity will increase a bit. The velocity then ususally stabilises with the systems self regulation. As the pressure finally falls the velocity falls.

The other sort of system uses a "regulator". The regulator is a small chamber into which air at a fixed, but lower pressure is vented. The knock valve is then used to allow the complete charge of air to power the pellet. Because the regulator allows you to use a metered volume of air at a fixed pressure the velocity/energy should be very consistent. There may be an issue with some regulator designs at a certain pressure the regulator pressure becomes higher than that left in the cylinder. This can sometimes actually cause higher than normal velocities as it is then working just like an unregulated gun.

Alan

[Andre]

The higher pressure in the tank the lower the velocity. It's called valve lock. Or in this case partial valve lock.
Another reason to not overfill air cylinders.

[Bruno Almeida]

Does rifles like Feinwerkbau and Walther have some kind of protection against overfilling in the regulator or trigger system ? What could happen, for example, if a shooter attaches a cilinder filled with 250 bar ? Simple valve lock or can some oring be blown ?

Thank you.

[RobStubbs]

Does rifles like Feinwerkbau and Walther have some kind of protection against overfilling in the regulator or trigger system ? What could happen, for example, if a shooter attaches a cilinder filled with 250 bar ? Simple valve lock or can some oring be blown ?

Thank you.

Theoretically they could explode, that why there's a maximum on them. Whether or not that would actually happen, I doubt, but equally I'm not about to put it to the test.

The 'valve lock' mentioned should not happen across the range of pressures used in a quality airgun - that's what regulators are designed to 'regulate' for. If you're concerned then chronograph your gun at full, and low fill.

Rob.