Hammers (and Springs)
I make these mainly for the Gunpower/Airforce range of rifles in brass, aluminium,
and bearing grade engineering plastics.
These come in a confusing array of different designs ....... heavy, light, sleeved, cored, waisted, internally
lightened, or hybrid types. There are pros and cons for each, some of which is discussed briefly in the Stealth section.
They all however, are designed to have minimal and unchanging frictional characteristics, to improve hammer strike consistency.
This is particularly true if used in conjunction with a quality replacement mainspring.
I find it absolutely astounding that a quality mainspring in a PCP like the Stealth, will actually half the shot fps standard deviation!
(This is the statistical variance of pellet velocity in feet per second)
Almost unbelievable that a simple spring can do this,
but it's true, and I've recently discovered the secret .....
My polished stainless steel mainsprings are slightly stronger than the GP music wire equivalent, and as such don't require
as much spring packing to obtain the necessary spring rate, so operate with less compression. This helps performance efficiency
and improves consistency of energy release on decompression, not to mention the other benefits of less fatigue and longer working life.
Unlike the standard frame guided hammers provided by Gunpower, which rattle down the frame on their way to collide at varying angles
with the breech slide, most of my hammers are barrel guided, which means they never touch the frame.
I now regard frame guided hammers as rather prehistoric in design compared to the barrel guided type, which give precise alignment
and presentation at the breech controled to very fine limits by the barrel clearance, cleaner and more consistent trigger sear release,
and are quieter in use because the hammer doesn't rattle against the frame. These hammers glide completely unlubricated on the polished
barrel, giving a very consistent hammer strike, and as an added bonus, have a much improved, superlative cocking feel.
My hammer with oil filled nylon core is a fine example of a barrel guided hammer, which will glide beautifully and silently on your
polished barrel, but because of the dimensions involved I can only make this type of hammer for the standard 12 inch barrel which has a
diameter of just over 12 mm. For barrels with bigger diameters the wall of the nylon core becomes too thin to be sustainable, as you need
a fair thickness of metal hammer wall to give it weight.
This is why the hybrid hammer was devised, and this will also glide effortlessly and silently on your barrel without any lubrication.
It's actually better because it has a plastic nose which is quieter on impact with the breech slide, and can be accommodated on any barrel
diameter in a vast range of different weights.
The hybrid hammer is made from brass and bearing grade engineering plastic. These two parts permanently snap together as a one piece
unit, and generally can't be separated later. These components are separately precision bored to different internal diameter dimensions,
so that when assembled and barrel mounted, only the bearing grade plastic part touches the barrel.
All my hammers now have a new nose design, and this is illustrated in some of my gallery pictures.
In addition to the 45° nose
chamfer, which mates positively with the trigger release sear when the hammer is retained in firing alignment against the barrel, the
hammer nose has a small contact footprint (with the breech slide), having a gentle inward curvature. This is designed specifically to
minimise the vacuum formed and released on impact with the breech slide, which is where the noise known as hammer slap comes from.
Hybrid hammers for the larger barrel diameters additionally have a new refinement of a textured bore , specifically designed and
engineered to further reduce running (kinetic) friction.
Although I still make other types, the hybrid hammer is the best type to have, and is suitable for all manner of different barrels as
they are individually custom-made.
Lighter hammer designs, which can be accommodated in 12 fpe (foot pounds muzzle energy) guns when barrel length is increased, give
quicker lock time for the firing cycle, and therefore further improve accuracy as there is less time for shooter input to pull the shot
off-course before it exits the barrel.
When a hammer is chosen and tuned correctly for a given valve and barrel set-up, there additionally can be a marginal
improvement in air economy, i.e. more shots per charge. This is the ideal, and it's what tuning is all about.
To accompany the polished solid stainless steel mainsprings made to my own design for the Gunpower Stealth and Condor, I provide
spacer packs for pre-tensioning and a spring centraliser with all hammer and mainspring purchases, to allow owners to fine tune hammer
When setting up your hammer and mainspring, you won't necessarily need all the pretensioning spacers I provide, so always bear this in mind.
Arrange it so that the preload is at a minimum, so reduce this until there is minimal pressure on the breech slide when the gun is de-cocked.
This will prevent excessive valve duration which will simply waste air.
The new style valve doesn't respond to preload to give more power due to it's internally restricted flow characteristics, it just gives you
more valve duration, which essentially means that your valve is still in the process of closing long after the pellet has left the barrel.
Higher hammer energies with excessive mainspring preload can also give rise to the valve rebound phenomenon.
A member of the TOG, whose
name unfortunately escapes me, filmed this with a high-speed camera, and it clearly showed the valve opening and closing as the breech slide
and hammer rebounded no less than three times, until the valve finally stuttered to its final closure!
These hammers and springs will enable superior performance for smoothness, quietness, efficiency and consistency, but please be aware that
in changing the characteristics of your gun, the muzzle velocity of projectiles may also change, with possible legal implications.
Owning an air-rifle producing over 12 ft/lbs muzzle energy, carries
VERY HEAVY PENALTIES.
It is therefore imperative that muzzle energies are checked on fitting
Gallery last updated 10th October 2008