..... If you tune them both to the same intensity, where the shorter barrel shoots a bit slower, then the shorter barrel might even be more accurate than the longer one because it is stiffer.
A friend has a Crown Continuum (380mm and 700mm liners) and the difference in fps between the 2 liners on the same tune is close to 100fps! The efficiency difference is astounding!
The chart below is for a typical medium tune .25 PCP air rifle. The calculated velocity and energy for a 20" barrel and shorter can be read off the chart. The chart shows 46 FPE from a 20" barrel; with a residual muzzle pressure of 400 PSI. Now, if the barrel were cut off to 10" (half) the projectile FPE would drop to 36.5; while the muzzle pressure would double to 800 PSI. Note that doubling the barrel length from 10 to 20" increases the FPE by only 26%. Or reducing the barrel from 20 to 10" reduces the FPE by only 20.7%. This is because for this PCP to reach medium FPE, the valve closes long before the projectile reaches the muzzle. Longer barrel data at this tune can be extrapolated. For instance, the pressure curve should decay such that the muzzle pressure is 200 PSI for a 40" barrel. Such a long barrel would be unwieldy, and gain very little over a 30" barrel. This is due to low effective driving pressure compared to projectile friction - unless the poppet valve was retuned to stay open a lot longer. Also, the porting would need to be "wide" enough to flow sufficient air, to increase velocity significantly, beyond that of the 20" barrel. Chart from: https://www.gatewaytoairguns.org/GTA/index.php?topic=94054.msg882296#msg882296
Logically, shorter would be stiffer…..shorter would give less barrel time...longer would give a lower pressure air release/pellet disturbance at exit…..but accuracy seems more barrel quality type random.
Although “brake” fans would like to divert as much of that gas could as they can...at the expense of more noise….am ambivalent about brakes and higher powered airguns.
I have noticed also that different projectile speed = different air blast coming out at muzzle, the cone I need to shorten or lengthen the distance.
I just know that positioning the cone at a given distance from the muzzle effects the POI