Axel wrote:Hi Andy
Yes, you're right, it's a springer (Weihrauch HW97 KT). I have noticed that some pellets(Crosman Destroyers and H&N Field Target Trophy) are a looser fit when inserting into the breach. Weihrauch don't specify the exact diameter of pellet to use. What is the science angle here? I can see that a tighter pellet will provide a better seal, but will a tighter pellet slow down due to the increased friction in the barrel? As you say, experimentation with different sizes is the best answer!
Cheers
Axel
The science angle is complex and what I write below is very much a simplification.
A PCP works with the pellet accelerating (relatively) gently up the barrel while a springer relies on a small blast of extremely high pressure air "spitting" the pellet. The skirts of pellets fired from a springer can be seen to have been inflated by the piston pressure, causing them to grip the radius of the breech, allowing the pressure to build up until it (the skirt) suddenly yields, resulting in extremely high initial acceleration. Conversely, skirts of pellets fired from a PCP tend to be undeformed, except of course by the barrel's rifling.
You need to fire the pellets into material which will gently decelerate them to see this. Once fired, both springer and PCP-fired pellets exhibit approximately the same barrel friction.
This is the reason you can get very short barreled springers while PCPs tend to have longer barrels.
To go back to the subject of barrel leading, I have observed that PCPs tend to suffer from lead build-up much more than springers. I remember somebody bringing a BSA R-10 to me to investigate why it was so inaccurate and I discovered that the lead build-up was so bad it was hard to discern that the barrel was rifled! However, as to why springers are so sensitive to de-leading (suffering from power loss) while PCPs prefer a perfectly clean barrel (and become inaccurate when leaded) is still very much a mystery - if anybody has any idea please educate me!
"Everything not invented by God is invented by an engineer." HRH Phil the Greek.