Yankee, I currently have a similar concern.
An RTI Prophet II
Compact (500mm) vs. a
Regular OAL (600mm).
Here are a few thoughts that I have gone through:
➊ A lighter projectile* will require less air.
➠ And thus will make
less noise.
*(with velocity the same)
➋
A lower velocity* of the projectile will require less air.
➠ And thus will make
less noise.
Do we really need to shoot stuff at or above
900fps? — Consider our UK brethren who kill gazillions of rabbits, pigeons, and other animals shooting at slow velocities of
750fps (and with a lowly .177 pellet with a lousy BC).
*(with weight the same)
➌ A longer barrel gives air more time to accelerate the pellet — thus I don't need as higher pressured air.
➠ And this will make less noise. ● Note, that a gun
with a short and therefore loud barrel that needs a silencer can still be very short for transportation
and for shooting in areas that are not noise-sensitive.
But a gun
with a long and therefore quiet barrel will always be long, no matter what. ➍ If I plink or hunt close range — and I don't plan on shooting either
precision shots or
long range — I could
change the tune:
Tune: I maintain my muzzle velocity, by increasing the regulator setting, while reducing the hammer spring to a low setting
(10% or 20% below the plateau velocity, unlike the recommended procedure of 5%).
The result will be a very short sip of air — at a very high pressure.
➠ This is significantly quieter than a regular (5%) tune. ● This tune will usually have the disadvantage of
larger muzzle velocity variations.
However, for plinking and at close range that won't be much of a factor:
For example (calculated with the StringCal of the GPS Ballistic Calculator):
• JSB Dome .25cal with 25.39gr
• 850fps average muzzle velocity (41FPE)
• 60fps muzzle velocity
variation (plus or minus 30fps)
➔ At a target range of 50y this fairly large variation results in only a small dispersion:
maximum 1/2 inch up or down from the POA on the target.
➎ If I understand correctly, a
sufficiently large plenum could be of help (more than 0.5cc plenum volume per FPE), as it makes sure the short sip of very high pressure air can be maintained long enough.
Matthias
