I have the Cardew book and have read it.
I must admit I too have a few disagreements with some of the data. In the book it claims that a lot of energy is used up getting the tail of the pellet into the actual rifling. So getting the tail over that opening of the breech ( especially the breeches that are countersunk with a distinct 'edge' rather than a smooth curve ). Cardew said that if he used a probe to push the pellet tail into the rifling ... then he had saved energy from the blast of air and he got higher muzzle velocities and more power.
I had an old Webley Vulcan in 0.177. Most of my springers lived up to the theory that a lighter pellet gave more energy. The Vulcan ( as per a lot of Webleys ) had a 'curved' opening to the breech. Most pellets you thumbed in, the tails would sit part way down that curve. I tried probing them into the rifling, like Cardew suggested, and expected a rise in muzzle energy, as I had saved on the energy getting the pellet into the rifling. The muzzle energy went down.
I then tried some 4.51 Barracudas which are longer and have a wider tail. The ends of the tails on these sat flush at the back of the curved entrance to the breech ( so further back than the other pellets ).
I'd tuned this little gun up and in 0.177 I was struggling to get 12fp with most pellets ... Superdomes, AA Fields, Wasps etc. Using the much heavier Barracudas that were tight in the breech I expected a woeful muzzle energy. I got 13.5fp. I'm sure it was because the pellet held it's own in that curved entrance to the rifling and a greater pressure of air built up behind it, so when it did release it went with great acceleration.
Maybe nonsense ... but those tight, heavy, Barracudas were far more efficient in that gun than the lighter pellets. Most accurate too.
The pellet out of the springer is 'hit' with an initial 'pulse' of air. A bit like a coin being hit in shuv a penny across a table. In a pcp the air is delivered as a more constant, more gentler push all along the barrel. Hence better energy can be achieved in springers with short barrels but the pcps get more energy from longer barrels. That's why the pellet tails on the springer pellets get 'crushed' up. That is why I said about 15 pages ago that the pellets from my 77 were hitting that paddle differently than the ones out of the pcps. Muzzle speeds were the same with the same type pellets. Were the pellets from the pcps, that would have retained the diablo shape, then hitting the paddle with less 'whack' ( technical term ) as they then started to fold on impact? The pellets from the 77 would have already been 'crushed' and compacted ( more bullet like ) so the 'hit' at the paddle was more 'solid'?
Last edited by skires; 5th October 2013 at 08:03 AM.