Dry Firing PCP

[Scratchy]

Hi

I know its not a good idea to dry fire a spring air rifle but does the same apply to a PCP as I want to set a trigger and need to fire the action as I do to check it. My mate has a BSA superten which I,ve seen him dry fire and when grilled about it he claims that you can do it with a PCP.

Any Ideas ?

Edited December 1, 2009 by Scratchy

[MM]

it will end up broke. it was not made to be dry fired, as the internals have nothing to push out. thats the simple answer.

[fo5ter]

There should be no problems with a PCP. The reason being that it is a release of compressed air stored in a chamber for release - with a springer it is the release of the spring and movement of the piston whih forces out the air. this expells a lot of energy which can damage the internals as the gun is designed to fire with a pellet in the breach thus the piston is somewhat cushioned by the resistance which is simply not present with an empty chamber.

A PCP rifle does not hae this problem - fire away!

[MM]

ok. dont say i didnt tell you.

[Scratchy]

Ok Fella's thanks for responses

[Tobyb525]

PCP

Spring :yp:

[Rem223]

it will end up broke. it was not made to be dry fired, as the internals have nothing to push out. thats the simple answer.

I would like the complicated answer as your simple answer doesn't explain very much. Your reasoning is fine in a spring rifle but I don't believe you can use the same argument with a PCP. I would think that the potential to cause harm would depend on the method that the rifle uses to discharge the shot of air. I have a Falcon which uses a simple spring loaded hammer to impact the valve mechanism. The other side of the valve is a pressurised chamber at upwards of 2700psi. So there is plenty of resistance to the hammer blow irrespective of whether or not there is a pellet in the bore. I have dry fired this countless times and have no evidence of damage incurred, but I can't speak for other makes of rifle. The simple answer in your friends case would be to contact BSA and get it from the horses mouth as it were.

[Billy.]

I will second the damage that can be done to a PCP.

 

When there's a pellet in the breech, the release of air will very suddenly become compressed, thus causing a slower release of air (I say slower, but it'll be thousandths of a second different) If you dry fire the PCP it just has this sudden burst of air, which can bring the transfer port down to much colder temperatures and then as it warms and expands again it can eventually begin to get stressed and fracture.

 

You have to remember that you are dealing with a gun that's pressurised to nearly 250 Bar. That's nearly 3,700 PSI. Well over 1000 times more pressurised than your car tyre. Once the gun picks up a stress fracture, it's only time before the pressure will break something.

Edited December 1, 2009 by harfordwmj

[MM]

I will second the damage that can be done to a PCP.

 

When there's a pellet in the breech, the release of air will very suddenly become compressed, thus causing a slower release of air (I say slower, but it'll be thousandths of a second different) If you dry fire the PCP it just has this sudden burst of air, which can bring the transfer port down to much colder temperatures and then as it warms and expands again it can eventually begin to get stressed and fracture.

 

You have to remember that you are dealing with a gun that's pressurised to nearly 250 Bar. That's nearly 3,700 PSI. Well over 1000 times more pressurised than your car tyre. Once the gun picks up a stress fracture, it's only time before the pressure will break something.

 

 

 

cheers Harford. i just couldnt be *****'d typing it all out so it could be understood.

 

i think i would have put it like this. Just because your car has a reverse gear, dont mean you should always drive backwards.

Edited December 1, 2009 by MM

[Scratchy]

Thanks to all for responses but , as it is not conclusive one way or the other, I think I will air ( excuse pun !) on the side of caution and load the rifle before firing. That way I can do no damage unless I shoot something !

[Ali-C]

When there's a pellet in the breech, the release of air will very suddenly become compressed, thus causing a slower release of air (I say slower, but it'll be thousandths of a second different) If you dry fire the PCP it just has this sudden burst of air, which can bring the transfer port down to much colder temperatures and then as it warms and expands again it can eventually begin to get stressed and fracture.

 

There is always a sudden burst of air, the pellet in the breech doesn't slow it through the transfer port.

When you fire a springer, the air is compressed in the compression chamber very rapidly, heating it to incredibly high temperatures for a fraction of a second, the pellet in the breech provides a slight resistance and a cushion of air forms, preventing the piston head from slamming into the comp chamber wall (That's why dry firing springers is a no-no, no cushion of air forms and the piston head crashes into the comp chamber wall). This is why springers give higher power with shorter barrels, it’s due to the rapid, ‘exploding’ nature of the firing cycle.

 

With a PCP, the hammer hits the valve and air is let through, air pressure on the other side then seals the valve. The pellet is smoothly accelerated up the length of the barrel (hence why PCPs tend to give higher power with longer barrels), the air is not compressed in the transfer port as the pellet has started its journey before the valve has closed, that’s essentially why the pellet is still accelerating as it goes up the barrel in a PCP.

And that's why you can safely dry fire PCPs, the pellet provides no resistance for the air to cushion moving parts, unlike a springer.

However, don’t dry fire a PCP with no air in as it is possible, not likely, but possible to damage the valve and valve spring as there is no air pressure to close the valve, meaning the valve spring can be overstreched and cause a leak.