Here's a sceptical point of view:
Coil springs work by applying TORSIONAL forces to the wire. Yes the spring itself works under compression, but the actual springiness comes from application of torsion to the wire.
The only way to have rotation of a spring when being compressed or released is if either: The wire length changes; the diameter of the spring changes.
Potentially, the wire length could change, and probably does, when torsion is applied *I would imagine* that there is a small amount of shortening of the wire.
As for the diameter of the spring changing, I see nothing other than either a side effect of the above, or else (does not/should not apply) where the diameter to be changed as a result of an outside force.
*I suspect* that the shortening of the wire upon compression will be very small. The angular rotation of one end of a spring typically used in an air rifle must also be small. 20 degrees anyone?
Certainly, taking into consideration the mass of the spring, it's total ROTATIONAL movement, compare to the mass of something like the piston and it's movement, and also the dampening mass of the rest of the gun, sorry, but I don't really buy into feeling this effect.
Not only, but here's something else. If the spring is NOT allowed to rotate, i.e. it is secured at BOTH ends then you have a closed system and as far as I can tell there can be no reaction at all! Of course there should also be no reaction if the spring were perfectly free - but considering the forces, this latter is far more difficult to achieve than making sure it does not move at all.
In reality I would not give this a second thought. The Cardews, applying scientific analysis to all aspects of airguns and tuning, in fact also dismissed this matter as being anything of concern.
Out of curiosity, I did my best to find info online about this, and came up with very, very little.
Here's the best I could find: http://www.eng-tips.com/viewthread.c...=162484&page=5
As an aside, it is common for spring preload on some coilover units to be adjustable via a threaded spring perch, i.e. where the spring sits, you can best see this on full suspension mountain bikes, the only thing that stops the adjustment from changing is the friction at the thread caused by the spring compression, there are no lockrings whatsoever.
If there was any major rotation of the spring, applying any major force, then this spring perch would lose it's adjustment in no time at all. On my bike fitted as per the pic - never ever is there any change in adjustment at all.
http://www.avalanchedownhillracing.c.../fox_dhx50.jpg
**WANTED**: WEBLEY PATRIOT MUZZLE END; Any Diana/Original mod.50 parts, especially OPEN SIGHTS