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General info on Gunpower guns, components, tuning and sample prices.

These guns have a definite following with a lot of enthusiastic owners, and I can provide all manner of different parts which will enhance and improve function and aesthetics.  The tamperproof features on the new guns only prevent barrel swap. Hammer and mainspring changes can still be made quite easily if you follow the instructions section on my website.

The Bottle.
The standard bottle used on this gun is 0.5 L capacity manufactured by Luxfer. Larger capacity bottles of 0.8 L are also available.
Air bottles for Surface-use, are subject to different rules from normal diving or Sub-sea use bottles.
From date of manufacture, Surface-use bottles need a visual inspection after five years, and then a hydraulic stretch test after a further five, and this pattern then repeats.
The intervals for Sub-sea use bottles are (from date of manufacture), 3 stretch, 2 visual and 2 stretch.  The two year cycle then repeats.

The normal fill pressure for the Buddy bottle is 3000 P.S.I., equivalent to 200 Bar, and you should not exceed this pressure.  If you do, you will find the gun is well under power until it gets back down to 200 Bar. You may even find the gun has no power output at all, as the valve will simply fail to open, a condition known as "lock-out".

Owners generally fill or top up the bottle when performance begins to notably drop off, which is at around 100 Bar. (This is easily noticeable by the changing sound of the muzzle report, reduced recoil and dropping POI).
There are lots of numbers on the bottle. The first is always the neck thread size, which for UK guns is usually M18 x 1.5 ISO. 
Your bottle will be marked PW250, this is Working Pressure (PW) or Charge Pressure (CP) maximum in Bar.
In addition to the date of manufacture, the bottle also carries another marking..... PH375, or PH348 which is the Hydraulic test Pressure in Bar. (You can see there is a huge margin of safety between Working and Test pressure).
For the airgun bottle you need a visual inspection five years after the date of manufacture, and after the next five years a hydraulic stretch test and certification.  So if your bottle is over 10 years old, you need to have this tested, and it's actually illegal to have it commercially filled if it doesn't have the correct certification..

I don't test bottles, for this you'll need to take your bottle to a Certified Test Centre. 
For home use, if you're using a hand pump to fill this and your bottle is in good condition, hasn't suffered any major trauma, then you don't really need any testing done, but if you take it to a fill station/dive shop then they may refuse to fill it until Test on the bottle is up-to-date.
Some fill stations, will contend your airgun bottle is capable of sub-sea use, and therefore falls under the two year interval rules, so will refuse to fill it and insist on it being tested.
Although their reasoning or motives may be questionable, you have to take this on the chin (or in the wallet) and accept this.
It is also not unknown to have a bottle fill refused, even if the bottle is in Test. On health and safety grounds it is their responsibility and prerogative, so again, you have to accept this.
There is a recent trend to fit quick-fill adapters onto these bottles via a tapping at the base of the cylinder.  This severely compromises the integrity and safety of the bottle, so I would strenuously recommend that you DO NOT do this.

Make no mistake, compressed air is dangerous stuff, and safe handling must always take priority.

Bottle emptying, valve removal and strip.

If you need to empty the bottle for any reason eg. valve spring adjustment, this can be done very easily.
Dry firing is one way, but takes forever.
Another way is to use a carpenters sash cramp, to squeeze the bottle end-to-end. First place a nut from a nut and bolt or washers on the top hat, and tighten the cramp until the valve pops. You WILL need ear defenders for this.
An easier way is to simply screw on your charging adapter, again with the nut or washers on the top hat, until the valve opens. Hearing protection is still required for this.

For valve removal, this can only be done when the bottle is empty.
If you intend to fully strip the valve later, before emptying the bottle, you first need to ensure the top hat can be released from the stem.  Most of the new valves are shamefully assembled by having the valve stem and Top-hat assembly literally hammered into the valve through the valve face.

This results in a number of problems which I come across fairly regularly i.e. scored and leaky valve stem channels, bent valve stems, bent valve return springs, damaged Delrin valve tip with a double lip, and very commonly this also damages the external threads on the tip of the valve stem.  This means that the hat is locked in place for life, and your stripdown options then are limited.  For the brass face type valve, the brass insert complete with stem can be removed, the Delrin valve tip removed, and the splines ground off.
If you have the black, all-steel valve your only option with a locked-on hat is to prize out the valve stem with Top-hat complete.  To achieve this, ease this out gently with a pair of flat blade screwdrivers, one either side of the top hat.  You have to use a pair of screwdrivers, not one, as otherwise you will bend the valve stem.

Please note under normal circumstances the valve stem should never be plucked out of the valve face, as the stem has splines at the base which are a bigger physical diameter than the rest of the shaft, and this will irreversibly damage the valve stem channel if removed in this way.  The stem should always be removed from the rear of the valve after the valve body has been removed from the bottle.

There are quite a few different body types of Gunpower valves. Some have a leverage socket hole on the side, some don't. Some have burst discs, some don't. Some have both features, some have none. .... so the features of your valve will determine the removal method.

If you are not properly equipped to remove the valve, then I suggest you leave this to me. A number of my customers have actually managed to write off their valves in a botched removal attempt, and it's easily done. Special tools are needed, and I can remove this and replace it without a mark. Do not, under any circumstances use an unprotected vice or Stilson wrench, or interfere with the burst-disc plug.

If you have the brass face valve, you can simply unscrew this part and send me only this part for the "O" ring mod..

Some instructions for removal of the top hat and brass insert....

With the bottle under full pressure, use the correct size of Allen key to release the two grub screws on the top hat.  You will require a 0.05 inch Imperial key for this.
If your valve stem has damaged nose threads, you won't be able to remove this.

It is now standard practice for Gunpower to Locktite valve components in place.   If the grub screws won't move or the top hat won't turn, don't force anything, as you will strip the grub screws and damage your key, or in the case of the top hat this will merely turn complete with the valve stem. 
To overcome this, with the bottle under full pressure, heat up the top hat with a blowlamp, cigarette lighter or chefs blow torch, for a few seconds until it just begins to smoke, and then you will find the grub screws turn quite easily and can then be removed. With the top hat still hot, insert the end of a small drill or panel pin into the grub screw holes and use this as leverage to unscrew the top hat which will now turn and remove quite easily.  Quench the valve in cold water as soon as you have removed the top hat, by inverting the bottle and immersing the valve in a tumbler of cold water.

Next, reattach the top hat loosely and empty the bottle. 
Once the bottle is empty, the brass insert part can simply be unscrewed from the bottle.  You will need a pair of circlip pliers for this and it is very easy to remove.

The Valve.
I'm often asked about the burst disc.
This is a failsafe device. Merely a means of safe pressure venting or release, to prevent the bottle from exploding in the event of being overfilled, or excessive pressure being produced when subjected to a lot of heat. This can happen for example in a house or vehicle fire, or even just being left in a closed car on a hot summers day, as the bottle pressure is highly temperature dependent, and this bottle is really akin to an unexploded bomb!  
The actual burst disc is a little disc of thin metal foil, guaranteed to rupture or fail at a certified pressure. This is pressure seated in the burst disc cavity, and doesn't like to be disturbed, so should be left well alone.

The burst disc has absolutely nothing to do with power output. A Stealth at 12 foot pounds muzzle energy (fpe) and an FAC rated one are absolutely identical, the bottles and their working pressures are identical, and although there may be other or different components in the gun build, the only real difference is the valve.

There is a somewhat disturbing phenomenon sometimes seen when filling by hand pump....

If the valve return spring pressure or spring setting is not sufficient, when approaching maximum fill pressure, the valve is sometimes unable to seal efficiently because pressures on both sides of the valve are closely matched with a slight imbalance in favour of the valve remaining open.
This allows the loss of a little bottle air, during that momentary pressure drop time interval which happens on the up-draw pump stroke.  With a hand pump this pressure drop imbalance takes quite a long time (about 1 second), which instantly frosts the valve seat surface, which then has no way of closing because ice crystals physically prevent it from sealing, so you loose the complete bottle contents. (AKA "valve dump")..... which for the un-iniated, can be a true brown trouser moment!!
The fix is simple, but you have to remove the complete valve from the bottle and apply more return spring pressure, either by valve spring retainer adjustment, shimming or spring replacement.

This occurrence doesn't happen with a fill station/dive shop, or bottle decanted fill, for several reasons.
First off, (good) dive shops use desiccated (dry) air, which has had nearly all of the moisture removed, so its ability to form frost or ice crystals on the valve seat is greatly reduced. 
Here the fill process is much quicker which generates plentiful heat (a frost enemy), and also, at the end of the fill, the pressure-drop / time curve, is a LOT sharper, a fraction of a second, so frosting (with the valve consequently jamming open) hasn't time to happen.

Valve dump can also happen occasionally when shooting with the bottle attached to the gun.
Again this is caused by pressures on either side of the valve being equal i.e. the internal bottle pressure matches the pressure applied to the valve tip seal (via the stem and top hat to which it is attached).
This is of course meant to happen with every shot, to allow the valve to open, but in this scenario you have an excessive time factor known as "valve duration", which holds the valve open for slightly too long, again frosting the valve seal, causing it to jam open. .... more on this later.

Pesky air leaks.
Leaky valves are very common and it is rare that a valve has to be replaced with a problem like this as most can be repaired.  First of all you need to establish where the leak is coming from.  To determine this, with the valve on the bottle under pressure simply invert it in a tumbler of water and look to see where the bubbles are coming from.

Leaks occur in one of four places, ... the bottle to valve body seal (very rare), the burst disc socket if you have one (quite common, ... and nearly always due to vandalism), the "O"ring under the brass valve face insert (very common), or the valve seat/tip seal (the usual place).   In the latter instance, bubbles will be seen to emerge from either the bore of the valve stem, or the annulus between the stem and the valve face.

This type of leak is usually caused by debris embedded in the valve tip, or more detrimentally damage to the metal lip of the female valve seat.  Sometimes it is caused by alignment problems, due to a bent valve stem or valve return spring, or inaccurate spring end grinding.

All can be cured, however damage to the metal valve seat lip is more serious. This only occurs with the old style all-steel valve body. Sometimes I can repair this but if this is beyond repair, then the valve is a write-off.  This is caused (ruling out vandalism) by bubbles or impurity inclusions in the steel casting at a crucial point i.e. the valve lip, which erodes over time quite quickly due to the regular passage of high velocity air in this crucial seal area.
This really is a warranty issue, so if the valve is still under warranty this should be replaced by Gunpower free of charge.
This however is a catch situation, because to establish this fault you have to inspect the valve seat, which will in turn invalidate your warranty. My advice therefore is, if you have a new, untouched bottle and valve, with tamperproof seals intact, and it has developed a leak, send it back for inspection/repair under warranty.

The burst disc socket is very vulnerable to damage, as it has fine shallow threads, which are easily torn, and the bottom of the cavity is very thin.
If excessive over-pressure is applied to the screw (the burst disc plug), the female threads can be stripped, but usually before this happens the base of the socket is forced inward causing it to bulge into the internal valve, physically jamming the valve tip and stem, thereby impeding free movement, and/or making an air seal in the burst disc socket impossible.
In either of these two instances of thread stripping or socket base damage, the valve is again a write-off.

If you want to send me your valve for assessment and repair, prices for this are as follows:

New Delrin valve tip £10.
New LCS (Leupy's Custom Shop) extended length design valve stem in stainless steel £35.
Valve spring re-grind /internal valve seat milling/lapping repair £10.
New LCS Top-hat in stainless steel extended length long polished design, complete with pointed stainless steel grub screws and Allen key £38.
New certified 250 Bar burst disc £8.
New polished stainless steel burst-disc plug with Allen key socket and socket refurb £20.
"O" ring mod if valve (or brass insert piece) sent on its own £15.
"O" ring mod. if valve sent complete on the bottle £30 (price includes bottle return postage).
Replacement of brass face insert "O"ring £2.
Valve periphery refinish by jewelling and lacquering , £15.
Valve refinish, the above, but also including jewelling on the valve face and on the bottle retaining ring £20.
Valve periphery refinish by chemical matte blacking £10.

The Gun .....Tuning, recommended upgrades and more sample prices.

This gun was originally designed as a full power FAC weapon, and was initially produced by Air Force in the USA.  The tamed down 12 foot pound version produced by Gunpower for UK use, really struggles to deliver the same user satisfaction at this power level, and because of this lower power is very susceptible to small variations in the chain of events or parameters involved in the firing cycle.....
Airguns, particularly 12 fpe airguns, because of their intrinsic combination of low energy lightweight projectiles, with high aerodynamic drag coefficients and low velocities, are particularly sensitive to small dynamic changes at the best of times, but this particular gun additionally has a lot of mechanical "function-critical" parameters, changing any one of which has a direct effect on all the others.
This gun really lends itself to tuning..... no complicated regulator or electronic triggers here, so it's a tuners delight or nightmare, depending on which way you look at it.
The tamperproof bush screw is a minor inconvenience on the newest guns which upsets a lot of owners as they are not able to fully strip their guns for lubrication or maintenance etc.  I empathise with this, so offer to remove the tamperproof bush screw if this is required.

To give you an idea, some of the parameters, any one of which will change the performance of the gun, include:
...... hammer weight, hammer frictional properties, (hammer energy and inertia), mainspring strength and mainspring pre-tension (spring rate), breech slide weight, breech slide kinetic frictional properties, breech slide dead volume, breech slide knob weight (yes really), valve type, top hat/valve face separation setting, valve stem type and porting size, valve stem bore diameter, valve stem return spring pressure, presence or not of valve closure assist tube, internal valve spring retainer/restrictor orifice size, presence or not of valve stem channel "O"ring,  bottle pressure, barrel caliber, barrel length, barrel choke, barrel rifling type, eg cut or hammer forged, barrel bore sizing i.e. country of origin, ammunition type and pellet weight.... to name a few, and I'm sure there are more!

This is why it's impossible to predict the result any tuning or parts upgrade will deliver. There are so many different setups of these guns, every gun is unique and you absolutely HAVE to chronograph your gun all the time, to ensure you adhere to the Legal limit if this is an issue.

If you attempt to rationalise the above parameters, you quickly realise the dynamic kinetic features all boil down to only one thing .... valve duration, and it is the art of controlling this that is the essence of tuning this gun.

The Stealth is a fantastic gun in its concept, an undoubted design classic, but sadly is of very poor build quality and can be nigh on impossible sometimes to obtain consistency close to the UK legal limit. 
This gun though comes in many different models, build types and forms.   The Condors and the high-powered guns that my customers in the USA and Holland have, with outputs well over 100 foot pounds muzzle energy (fpe), are absolutely phenomenal guns which bear hardly any resemblance to the 12 fpe UK model.
The design inherently does have some minor issues, but can be made a lot better by eliminating or controlling some of the above function-critical parameters, so will benefit greatly from a number of improvements or modifications which I provide to address these issues, and in order of priority I would list these as follows:

Replacement of the Gunpower frame guided hammer with an LCS barrel guided hybrid type.  (The best type I make, priced at £38 for the standard 12 inch barrel, £45 for a medium weight hammer for bigger diameter barrels, or £55 for heavyweight up to 100g.).

Improved quality solid polished stainless steel mainspring.  (Comes complete with centraliser and pretension adjustment spacer, £18).

The valve-stem "O" ring mod. [£15 if you send the valve only (or the brass insert on its own if you have this type of valve), or £30 if you send the valve complete on the bottle].

Replacement grooved wide blade aluminium trigger shoe (comes complete with polished stainless steel and brass fitment, with Allen key to suit).  (£40).

Conversion of the muzzle bush to the ventilated/pickle style. (£15). (This only applies to aluminium bushes on the Stealth or Shadow, where the barrel exits inside the frame. For this you need to send your original bush for modification, or alternatively at extra expense, I can provide a new bush at £30).

Safety release blade modification, with extended aluminium blade. (£20). (You need to send your original safety release lever for modification).

Replacement breech slide.  I provide a black Delrin breech slide, which is very similar to the Gunpower item, just better made, however my one has different hardness "O"ring's front and rear, and these are properly depthed for correct running friction with the barrel and air seal with the top hat.  (£65). This will perform better and more consistently than the Gunpower equivalent.

All these parts can be self fitted and there are stripdown instructions on my website, but I can provide personal instruction if you require.

My hybrid hammer complete with quality mainspring and the valve "O" ring mod. will completely and utterly transform your gun for the better.
The gun will be a lot smoother and quieter during the firing cycle, and you'll even notice the improved smoothness on the cocking stroke.
The stock Gunpower hammer takes its guidance from the frame which it rattles down every time you fire a shot, colliding noisily and awkwardly at unpredictable and varying angles with the breech slide.  It is therefore a very crude, badly designed arrangement, which is noisy and inconsistent in its energy delivery.

The LCS hybrid hammer is entirely different.  It is a refined, precision made barrel run hammer with a fine running clearance on the barrel, so it never touches the frame, thus delivering consistent hammer strike energy and clean trigger sear release. It is designed for minimal kinetic friction and requires no lubrication because it is self lubricating, which is also good for shot consistency.
The fine running clearance on the barrel means it never rattles in use, and with its position set symmetrically on the barrel the specially designed plastic nose makes precisely controlled impact with the breech slide with minimal impact noise, all features which make it significantly quieter, more consistent and much superior to the stock hammer.

My mainspring is captive at both ends, engaging with the hammer and also the mainspring centraliser, so you get no spring twang or frame scraping noises during the shot, and the classic spring/frame screeching noise you get when cocking the standard gun will be a thing of the past.
The LCS stainless steel mainspring is stronger than the Gunpower equivalent, so doesn't need as much pretension in order to deliver the correct spring rate.  This I have found is a key feature in delivering good shot consistency, and if you chronograph your gun before and after you swap over these components, you'll see the standard deviation for shot fps is much reduced with the hybrid hammer/quality mainspring combination.

The "O" ring mod. will give you more shots per charge due to less air waste, and your shot follow-through technique and accuracy will be improved because of the smoothness of the gun and the absence of the noisy air blast right beside your ear from around the valve stem during the shot.  Normally there is a subliminal flinch reaction on firing which is difficult to suppress, but a quieter gun diminishes this considerably. It will also give you a slight increment in your power output, as the air that was previously wasted will now exit through the valve stem rather than around it. 
In common with my longer style Top-hat which also raises the power output slightly, it is imperative you chronograph your gun after these modifications.
The "O"ring mod is discussed in more detail on my website here .....


My grooved wide blade aluminium trigger shoe feels much better than the original plastic Gunpower offering, and looks the part.  This is completely adjustable for height and angle and comes complete with all fittings and key.  Not only does it transform the feel of the gun, owners tell me it improves grouping accuracy, because the tactile feel makes you focus more on trigger release and follow through technique.

Conversion of the muzzle bush to the ventilated style, will significantly quieten the gun on discharge.  It basically allows the muzzle discharge which is inside the frame in the both the Stealth and Shadow, to move backwards towards the breech bush, thus utilising the frame volume as part of the moderator volume, in a manner similar to the Reflex style design of sound moderator. The frame then acts as a moderator, and this enhanced suppression of the muzzle blast greatly quietens the gun.

This mod is only suitable if you have aluminium bushes and you have a barrel that exits inside the frame e.g. the Stealth or Shadow.  In this instance you can additionally use a moderator attached to your frame as well, either the Gunpower moderator, or a standard commercial moderator attached by means of one of the frame adapters I make which are designed for half inch UNF moderator attachment.

The best style of frame adapter is the flush type with the black delrin intermediate piece which the taper base of your moderator blends into to give you a continuous look with the frame.  This is priced at £65, and you need to send your moderator for fitment.

Some of my other parts as discussed briefly below will enhance the quality of the gun even further.

A replacement polished steel Top-hat in my extended length design offers a visual improvement, and feels better on loading.
I personally think it gives a better pellet skirt set.  This is because the extended length gives a reduction in dead volume in the breech slide, which in turn gives a higher breech slide air pressure behind the pellet, and this additionally gives you a marginal increase in fps or power output.
LCS top hats are now available in stainless steel priced at £38, and come complete with pointed stainless steel grub screws and Allen key to suit.
 (I use M3 grub screws which utilise an M1.5 Allen key, which is a lot bigger giving better grip compared to the tiny Gunpower Imperial key which usually strips the Whitworth grub screw sockets).
The LCS design Top-hat will fit your existing valve stem, but is really intended for use with the extended length LCS valve stem also now available in stainless steel, which comes complete with improved design valve tip priced £45.

I make various designs of breech slide knob, in either the capstan or the fully sculpted styles.  I used to make these in stainless steel but now favour aluminium or engineering plastics due to weight and inertia considerations.   The capstan style is £15, sculpted £35, and double sculpted £45.
p&p of small items for UK postage is £4, anything else at cost, POA.

The list goes on, and also includes a replacement barrel which will deliver a major enhancement to the gun.  A new longer barrel on your gun, will give you many benefits, ...increased power and more shots per charge due to improved pneumatic efficiency, and better accuracy. 
A new fully machined barrel including custom-made heavyweight aluminium bushes crowned at both ends with a polished 11 degree target crown and screw cut for moderator attachment, is £245, more details on request.

If you want to go that step further, and have the gun converted to a firearm, this is very worthwhile, as FAC airguns are utterly fantastic, and will take this particular gun into a league of its own.  To do this you need to get a Variation, or authority to "purchase" your Stealth on your Firearm Certificate, but before that, you send me the valve to be worked on.  When your paperwork is in order, the valve and/or new barrel is then posted to an RFD of your choice who will hand over the components and fill in your Firearm Certificate, and from that moment on your Stealth is a listed a firearm.
Please note, I will not do this the other way round, the paperwork completion has to come first.

It is also important not to overlook simple things such as lubrication. 
LCS hammers don't require any lubrication, and because of this you get an added level of shot consistency particularly when coupled with a quality mainspring, however the breech slide is heavily dependent on lubrication for good consistency.  You must only use silicon oil for this, as petroleum-based lubricants will erode the "O"rings, and must not be used in a compressed air environment where combustion can take place due to the dieselling effect.  I can supply a 15ml bottle of suitable Silicone Oil, price £4 plus p&p.

These are just some of the popular parts I make or supply, there are others, and of course I also make parts to custom order, so please make contact for further details and prices etc.

Please remember if you intend tuning or replacing components, it is absolutely imperative you have access to a chronograph to check your power output, as some of these guns can be very easily pushed well over the legal limit.  There are a lot of guns on the second-hand market which have been tweaked to excessive output, so it's very important this is checked.
Chronographing is good fun, gives you a lot of feedback about the progress of your tuning, but more importantly keeps you on the right side of the law.  If you don't own a chronograph or have access to one, then this should be your very first purchase before you even consider fitting new parts.

Whilst every care has been taken in preparation of the above information, I can accept no legal liability for the accuracy of this content, or the consequences of any actions taken on the basis of this information, however caused.


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