Components:
Hammers - Bushes - Other components

The components I make are quite a diverse range, and include hammers, barrel bushes, end caps, frame adapters for sound moderator attachment, valve components (valve tip, stem, top hat), main-spring spacers, replacement stainless steel breech slide knobs, and an improved safety release.

Hammers (also discussed in separate Hammer section)

These I make in various designs, and in various materials, usually brass or aluminium. I originally made these almost exclusively to Bob Craske's design, either with or without the recess for the mainspring, but now this early type has diversified to include heavyweight or lightweight, in both plain and waisted styles.

Until fairly recently, this was an area of intense development, with radically new designs being generated. These included hammer types sleeved either externally with a fabulous hard wearing PTFE coating, or internally with oil filled Nylon, but now the barrel run hybrid hammer type has superseded the earlier frame guided type, and reigns supreme.

This hybrid type is a two piece hammer made from bearing grade engineering plastic and brass, which permanently snaps together as a one piece unit, and can be made in a vast range of weights to suit different valve types and barrel diameters.

Since its inception the hybrid type has been refined to include new features of special nose geometry, designed for quietness, and a specially textured internal bore for the larger diameters, to further reduce running (kinetic) friction.

There are various high-tech, high performance engineering plastics that I make this type of hammer in.
These plastics are generally of a bearing grade which have the addition of graphite, carbon, PTFE and molybdenum di-sulphide.

Plastic hammers are exceptionally hard and abrasion resistant and are quieter in use, as they produce less impact noise with the breech slide. They are also self lubricating, so, like my internally or externally sleeved hammers, are therefore run dry without the addition of any external lubrication. Because the frictional characteristics are unchanging, this helps shot consistency, and these high-tech plastics offer a durable, low weight, low friction alternative to the stock hammer, with very quick lock times.

The preferred order of assembly, for hammers, springs, pretensioning spacers and spring centraliser on the barrel, is as shown below:

 

If you obtain a hammer from me it will come with spacers and a mainspring centraliser. However, you may require some of your original mainspring spacers in addition to the ones I provide, and you will need to experiment with different dimensional combinations of these to obtain optimal mainspring preloading. You will also need to top hat tune at the same time, to obtain the required performance.

It is impossible to provide the exact components, to achieve for example, 11.9 foot pounds energy at the muzzle, because the Stealth is so different from gun to gun, and the valve setup can be entirely different again. It is therefore up to the owner to obtain the optimal setup, and it is crucial that you chrono your gun during setup to ensure UK legal muzzle energy output is not exceeded, if this is an issue. This also applies when replacing any other components involved in the firing cycle.

I make all of these hammers as custom-made items, specific for the barrel you have, so for hammers you need to specify your requirement. These hammers all basically just open the air valve momentarily, but different hammer types do this in different ways, and there are pros and cons to be considered.

I can't make the choice of hammer type for you as it depends on the type, calibre and length of barrel it is to be used with, the gun and valve setup, the type of shooting you do, and the power output you are looking for.

As a general rule, plastic and sleeved hammers are the most consistent, as the frictional characteristics are minimal and unchanging. Plastic hammers are the quietest, and waisted hammers give slightly cleaner trigger (hammer) sear release. Light hammers produce the quickest lock time and have minimum recoil, whereas heavy hammers e.g. most brass designs, have slower lock time and greater recoil, but produce more valve duration and therefore more power.

Lock time is generally considered to be the time interval between the trigger sear releasing, and the projectile exiting the muzzle crown. In powder burning firearms, after the firing pin hits the cartridge primer, lock time is a very quick chemically controlled cycle.

In air guns this is can also be very quick, but here there are only mechanical processes taking place, and by choice of components like mainsprings, valve springs and hammers, you can control this to a degree. Lock time, as far as hammer types in air guns is concerned, is the time interval between the trigger sear releasing the hammer, and its subsequent impact with the breech block or air valve, just milliseconds later. The latter stage of the lock time, i.e. the valve opening and the pellet being projected down the barrel and exiting the muzzle, will also change because of the inertia characteristics of the hammer type and its effect on the valve.

The extra recoil from heavy hammers translates as more muzzle flip in freestanding shots, or shots taken without the use of a bipod, and valve duration is the amount of time the valve remains fully open. As in everything Stealth, valve duration has to be optimised, as a valve that remains open after the pellet has left the muzzle is simply wasting air.

There is more to wasting air than poor air economy. If you have excessive valve duration from too heavy a hammer or excessive mainspring preloading, you run the risk of experiencing that quaint Stealth phenomenon, "valve dump". This is when the valve remains open after a shot is fired, and the bottle contents are jettisoned or dumped in their entirety. This is definitely not for the fainthearted or for anyone with a cardiac condition. It happens because of latent heat of evaporation, as what you have on your bottle could also be called an expansion or refrigeration valve.

Have you ever noticed that heat is generated when you pump up your bottle? This is the flip side of the same coin, because energy can neither be created or destroyed.

In a pressurised system, when a gas makes the transition from a compressed liquid or high-pressure state, to atmospheric pressure, it absorbs heat from itself and the surrounding environment in order to expand. This causes an instantaneous and rapid temperature drop at the expansion point.

This normally goes unnoticed, but depending on the temperature and relative humidity of the bottle air, this can become critical, and ice crystals then form on the valve seating surfaces during that momentary valve opening cycle. Their physical presence in this crucial area causes the seal capability to fail, so the entire bottle discharges. Stripdown of the valve assembly will reveal nothing, as the ice crystals that caused this seal failure are now long gone. This is one of the reasons I'm sure why Gunpower use such massive and excessively strong springs in the valve assembly.

What can one do about it? Minimise the valve open time factor (duration), use dry air, move somewhere warm.

Bushes

If I prepare a barrel by profiling it to fit the Stealth breech slide area, you will need  new bushes.  I custom make these in aluminium specifically to suit each individual barrel for mounting in the frame.

Gunpower provide different types of bushes with their barrels. These are usually plastic, but on occasion I have seen black anodised aluminium bushes. The latter are however slightly undersize, so don't fit the frame correctly, and the plastic bushes are perhaps not as dimensionally stable as metal, so some movement of the barrel can be experienced leading to zero shift.

My aluminium bushes are grub screwed directly to the barrel and are a very snug fit in the frame. I used to occasionally tap these No10 x 32UNF to suit the frame tappings, but now I provide either one or two clearance holes per bush, set at 90° for the frame screws, which is a perfectly adequate means of attachment. Rather bizarrely, some guns only have bush attachment screws from the underside of the gun, but other guns can have side tappings in the frame, and these can be on either the left or right hand side of the gun. Gunpower also use this clearance hole method for their aluminium bushes, and obviate the problem with plastic bushes which are essentially self tapping.

I also make pickle bushes in brass or aluminium for use with the standard 12 inch Walther barrel of the Stealth.  This is the barrel that exits inside the frame with the muzzle hidden behind the frame end cap.
The pickle bush is a laterally drilled, ventilated bush, which replaces the forward or muzzle bush of the barrel.
It allows the air volume inside the frame from the barrel muzzle to the breech bush to be used in its entirety as part of the silencer volume, and thereby makes the gun a lot quieter in use.  Without a pickle bush only the volume up to the muzzle bush is available.

Other components

The frame adapter replaces the existing steel ring and end cap, converting it to a male 1/2"UNF for sound moderator attachment. This is similar to my other Stealth frame adapter which screws directly into the steel ring after removal of the end cap. (Shown in the adapter section).

I do some valve tuning work  e.g. air flowing the spring retainer, replacing and precision re-grinding the valve return spring, to improve the presentation of the delrin valve tip etc.

For customers in The Netherlands or other countries where there are no restrictions on airgun power output, the valve stem can have its restriction removed, transfer ports bevelled and polished, stem internals and valve spring retainer bores enlarged and polished. This process is called Air Flowing.

The aim of this work is to improve the efficiency of air flow which of course generates more power output from the bottle valve. However, even for 12 fpe use this is an improvement which can be accommodated to good effect, because it allows you to reduce the top-hat separation for a shorter (quicker) valve stroke while still remaining at UK legal power output. Even though the power is returned to the same level, there are many benefits achieved, and the combined effect of hammer and valve work is to improve air usage efficiency, reduce lock time, and improve shot to shot consistency.

My top hats are a slightly longer polished design, which I make in Grade 316 (A4) stainless steel. These have a slightly longer portion where it enters the breech slide. When used in conjunction with one of my valve stems, which are also slightly longer. The extra length gives a little more adjustment in both directions.

The main advantage I think though is it seats better in the breech slide giving a more positive feel, AND, more importantly, it slightly decreases the dead volume there.

This means the charge of air delivered by your bottle valve isn't quite so diluted in the dead, or transfer volume in the breech slide before it hits the pellet skirt.

This is an important part of the firing cycle, imparting the initial inertia to the projectile, which needs a short, sharp blast of air to deform and set the pellet skirt into the barrel rifling lands, to give it that all important signature or bite. 

We're talking marginal differences here though, but nevertheless important to some of the more discerning owners.