GTA
Airguns by Make and Model => Benjamin Airguns => Topic started by: DOKF on May 30, 2014, 03:58:11 AM
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I have compared my four gas ram guns in three calibres using a wide range of pellet designs and weights. First I measured the muzzle velocities for as many pellet types as possible for each gun. Then I calculated the muzzle momentum and energies, and plotted velocity, momentum, and energy against pellet weight.
The plots seem to indicate that my Benjamin NV 0.177 and Benjamin NV 0.22 utilize the same power plants with a smooth transition of the velocity ~ mass relationship going from one calibre to the next. As expected, the pellet velocities drop significantly with increased pellet weight. Pellet velocity approaches the speed of sound (~340 m/s) with the lighter pellets, but drops to as low as Mach 0.3 for the heavier pellets. Interestingly, the velocity decreases less for the heavier pellets than for the lighter ones; increased mass from 10 to 15 grains is accompanied by more than 20% velocity difference, while increased mass from 25 to 30 grains is accompanied by less than 5% velocity change.
Velocity plots for the Benjamin NP XL 0.22 and Benjamin NP XL 0.25 also seemed to indicate a shared power plant design for the two rifles, although the two velocity curves do not intercept and overlap as closely as the NV 0.177 and NV 0.22 curves. Still, the NP XL 0.22/0.25 curve parallels the NV 0.177/0.22 curve, including a marked flattening of the velocity towards the heavier weight pellets.
The momentum and kinetic energy curves for the NP XL and NV rifles show slightly more detail. For the NV rifles, the curves overlap in the transition from 0.177 to 0.22, such that the 0.22 seems to be an exact extension of the 0.177 with heavier pellets. The muzzle energies of both the NV 0.177 and NV 0.22 max out at about 22 J, and then decrease gradually from there for larger mass pellets. For the XL rifles, the momentum and kinetic energies overlap closely for pellets up to 25 grains, after which the 0.22 calibre performance drops off dramatically.