Heya GW,
The advent of maximum velocity pellet guns has been somewhat of a game over the last 40 years.Some time ago Weirach produced a rifle called the "Barracuda" that used small dose injection of "Ether" (The medial compound not all the free energy stuff
) and also designed a 22 Grain slug that still holds that name to this day (The H+N Barracuda).
The uypper sensible limit of pellet guns is approx 1035 fps at ambient pressure as after that vorticular motion and drag become a huge issue.(They may go fast but do they go straight?)
Simple physics are usually the cause of the "Extreme velocity" guns that are on the market.
Take for example a typical .177 pellet weighing 7 grains.
MV of 850 fps / squared *
Projectile weight in grains / 450240
11.23 FtlB roughly...thats under the UK's harsh limit for a pellet gun without a licence.
1600 fps with the same slug
39.8 ftlb (ties in with the old "double the velocity and get 4x the energy)
The barrel will have NOTHING to do with the velocity,the barrel does not provide the energy and it's the energy that gives the pellet the ability to do "Work".
Length of barrels can make a small difference to a pellet gun but by far the biggest contributors are
In a spring gun:
Swept volume of the cylinder.
Diameter of the air transfer port.
Open pressure values of the spring.
In a precharge (Air not c02)
Volume of air discharged.
Pressure of air discharged.
Length of barrel to allow expansion and acceleration.(remember the laws of diminishing returns though,over a certain length and drag becomes a problem)
As to the claim that the pellets alone deliver a 25% velocity increase this will certainly be a matter of weight.
Input power * efficiency = output energy (simplified)
Anybody that tries to sell you a pellet gun barrel claiming it will give more than a 10% increase in power/velocity with the same projectile is a fraud.Most spring guns operate at around 15% efficiency,most precharges operate up to around 75% efficiency.
There are some other things that can affect the energy/velocity/projectile weight issues but all of those are still based in standard physics.
The Raptor pellet btw is gold plated pot metal or Zinc alloy.Higher velocity is aproduct of it's weight.
cheers Dave