Hold Sensitivity

Hold Sensitivity in Spring Rifles
Hold sensitivity is an interesting phenomenon, it is apparent in almost all shooting disciplines to some extent. From pistols to bows, nothing is exempt from hold sensitivity. I will share the knowledge I have gained through practical experience, both with shooting and tuning various weapons as well as information gathered from others in this article. My knowledge on this topic is far from infallible, should you spot an error or have something further you think should be added please let me know.

lets look at the firing cycle of a springer, the order will change depending on the specific gun and how its set up but this is a close enough representation of the average budget spring gun. This holds true for both spring and gas ram powered guns.
The image below is an example of how the direction of the bore moves during the firing cycle, the numbers refer to points during the firing cycle as listed. Please note that this image is purely for demonstration purposes and may differ drastically from gun to gun and indeed from shooter to shooter.

 

  1. Shooter aims at target.
    2. Trigger is pressed and the sear disengages from the piston.
    3. Piston starts moving forward.
    4. Gun starts moving backwards – bore moves away from point of aim.
    5. Pressure builds in front of the piston – piston slows down.
    6. Pellet begins to move forward down the barrel.
    7. Pressure in front of the piston drops and the piston hits the end of the cylinder.
    8. Gun changes direction lurching forward.
    9. Pellet exits the barrel .
    10. Pellet impacts target .

 

 

 

As you can see there are a great many things going on inside the rifle before the pellet even leaves the barrel. The offset in point of aim (specifically the exact direction of the bore) changes rather dramatically during the firing cycle. Your bore will not be pointing anywhere near your point of aim at the point of maximum offset and in most cases won’t be exactly on point of aim when the pellet leaves the barrel.

The amount of offset is determined by 2 things:

· Recoil
Large springs, long strokes, heavy pistons etc all contribute to heavy recoil. Often in the pursuit of maximising muzzle energy manufacturers neglect accuracy, now while a heavy recoiling rifle is not necessarily less accurate it will definitely be more difficult to shoot accurately.

· Lock Time
The lock time is the duration between pulling the trigger and the pellet exiting the barrel. The longer the lock time the more offset between point of aim and bore direction when the pellet exits the barrel. The longer the lock time the more opportunity the rifle has of pulling itself off your point of aim.

Hold sensitivity is a combination of these two factors. Recoil defines the amount of movement during the firing cycle, and lock time defines the total time that the recoil can still deflect the pellet. After the pellet has left the barrel it can no longer be affected by movement of the gun. A rifle that doesn’t move much and still gets the pellet out quickly will have very little opportunity to move the bore and will be very easy to shoot accurately. A rifle that has heavy recoil and long lock time will be able to move the bore much further off your point of aim and as such will be very difficult to shoot accurately.

· Low hold sensitivity (small offset, little recoil, fast lock time)
· High hold sensitivity (large offset, high recoil, slow lock time)

It is important to note that some guns may have a very fast lock time and still be very hold sensitive because of high recoil that moves the bore off point of aim. So although the pellet leaves the barrel very quickly, the rifle can still offset the bore during this time. Conversely a rifle with very little recoil and a very long lock time may be very hold sensitive. The time between pulling the trigger and the pellet leaving the barrel can be so long that you jerk the rifle or relax your muscles, pulling the bore off your point of aim before the pellet leaves the barrel.

All springer’s require a certain degree of skill to shoot accurately, a skill most unlike those used for any other rifle shooting discipline. The technicalities of shooting spring guns are beyond the realm of this article but they have been very well documented HERE.  While I don’t mean to oversimplify this art, there is certainly one factor that eclipses all others, and that is repeatability. Shooting the gun the same way every time you pull the trigger, holding the gun the same way, pulling the trigger the same way etc. this alone is what separates good shooters from bad.

Understanding hold sensitivity requires an understanding of the art of perfectly replicating your shots every time you shoot because hold sensitivity is essentially the margin for error you have when shooting. A rifle that is very sensitive will punish you for the slightest error, on the other hand a rifle that has a very low hold sensitivity will perform well even when there are variances in your hold, trigger pull etc.

When you change your hold, you change the way the gun moves during the firing cycle and more importantly the direction of the barrel when the pellet exits it. For example if you press the gun more firmly into your shoulder the lateral movement of the rifle will be impeded and the barrel is likely to rise more. If this rifle has very high recoil the offset will be much larger than a rifle that recoils less. If you shoot 10 shots at the same spot on a target with a rifle that is very hold sensitive you will achieve very poor groups if you are unable to replicate your hold. It is for this reason that you will never hear an experienced spring gun shooter talk about a rifle being inaccurate because of its recoil, but rather that the recoil makes the rifle more difficult to shoot accurately. For example a rifle with high recoil and long lock time in the hands of a shooter that can perfectly replicate his hold between shots can still shoot very accurately. Developing this degree of aptitude is exceptionally difficult, and will require a huge commitment to practice. It is often much easier to steer clear of the muzzle velocity rat race and opt for a rifle that will be easier to master.

How do I reduce hold sensitivity?

This question has been plaguing airgun smiths and competitive shooters alike for many years. I have personally spent a great deal of time working on understanding and reducing hold sensitivity in various spring guns, as have many others with varying degrees of success. There are techniques that have been tried and tested and are known to work well in most cases…there are techniques that have been used with great success in some guns and abysmal failures in others.

As we now understand exactly what causes hold sensitivity it is very easy to see the direction one must take to improve it…Reduce recoil and decrease lock time

Reducing recoil is achieved in many ways; adding weight to the stock to increase the rifles inertia (the propensity of an object to resist change in motion), reducing spring preload, lightening the piston etc

Unfortunately this is the point where managing hold sensitivity starts to sound like black magic to the uninitiated because in our efforts to reduce recoil we often reduce muzzle velocity and increase lock time. It inevitably becomes a delicate balancing act between muzzle velocity and hold sensitivity. Lowering the spring tension reduces recoil but often increases lock time and reduces muzzle energy. Lightening the piston can drastically reduce recoil as the piston weight is directly responsible for the amount of force transferred to the rifle (Newton’s 3rd law) however the lighter the piston the less effective it is at overcoming the pressure that builds up in front of it, so once again muzzle energy suffers.

There are so many ways to improve the hold sensitivity of a rifle, often a combination of small modifications culminate in a drastic improvement. However In the pursuit of perfection many people (myself included) become obsessed with tinkering with their rifle and forget that the fundamental ingredient to accurate shooting is now and has always been, a generous helping of practice. With enough practice, just about any spring rifle can be shot accurately.

 

Author: St-John Salisbury