Giffard Airguns - Miscellaneous
Giffard Airguns - Miscellaneous
Paul Giffard also manufactured this medical device - apparently a gynaecological 'irrigateur'. It has mistakenly been identified by a German gun shop as a CO2 filler device for Giffard guns! (With thanks to Eberhard for the correction on this point!).
The sales blurb:
Notes from CO2 Giffard shooters.
With thanks to two Giffard owners.
Owner 1: "The ball from Germany (H & N 4.55) is spot on, and the small Giffard rifle now functions perfectly. It is amazingly powerful, despite its trifleing report.
My ball mould (#4 Lee buckshot 6 gang, 18 ball) arrived a week or so ago, and although the first crop of ball were not as accurate as I would like, I think I have mastered the technique of casting and sprue cutting so as to give quite acceptable results. They are a perfect fit at 6.05 +/- 0.05mm and can be made in large quantities. My .319 Lee ball mould produces really lovely castings which are ideal for the 8mm Giffard, so all bases now covered.
I had a brain-wave regarding the acide carbonique, and was lucky enough almost immediately to exploit it! Out-of-date-fire extinguishers of the right type! Five were being thrown away from a new [local] restaurant... (2Kg gas each), and I gave the chap £30 for the lot. The only problem is that he wants to get me more... My very kind and talented engineer friend made an adapter, and I am now filling the cartouches pretty well.
A friend's cartouche for a 6mm carabine was faulty, and I used a newly-made cartouche clamp to open it and fix the problem. Basically it had been put together without PTFE thread sealer. It now has some carbon dioxide in its belly and is lying now happily next to the others."
Owner 2 responds: "There is just one thing... that I don't agree with, that is you need PTFE tape to seal the thread of the reservoir. I make my seals for Giffards from polyurethane and when they are made the correct size they never require any tape.
I have resealed many Giffards in my time with no problems, but saying that, everyone has their own methods. I also have a couple of fire extinguishers as standby Co2 fillers, but I mainly use a 5Kg tank which I get refilled from a fire extinguisher refilling company in my area."
Chris Buxton in the US built and air reservoir in place of the CO2 one. He wrote in the Yellow forum:
My 8mm Giffard Co2 rifle reservoir is over 120 years old and never been touched, so I decided to make a replacement cylinder for everyday use.
The Giffard will shoot the 49grain ball at around 600fps producing around 40 Ftib at the muzzle on co2. Perfectly adequate for plinking and the co2 fill provides plenty of shots.
For me, filling the co2 reservoir can be a pain, as I use the large co2 tank mainly for craft brewing so need to swap fittings and invert bottle etc. So for ease of use I thought I'd swap to air.
The original cylinder was obviously intended for co2, but you can fill the cylinder with air to around 60 Bar and have enough air for a couple of shots. But thats it, any more air pressure then valve lock sets in and muzzle velocity drops off ...+ the cylinder was not intented for any any more pressure. Since your not going to start modifying your antique rifle fitting a new hammer spring, your out of look with the original cylinder.
So I designed the new cylinder to run on air with a assisted valve, which can be opened at much higher pressures by the relatively weak Giffard hammer / spring. So you leave the Giffard rifle untouched.
The new cylinder is the same diameter as the old one, but longer, stopping just short of the sling mount to give 130cc reservoir volume. Hopefully its aesthetically well in keeping, for the age and grace of the old girl.
With the cylinder fully topped up at 200bar, the rifle can thump out the ball just subsonic at 1030 fps, producing a whopping 115 Ftib.
Turned down a little you can get 15 shots at over 800 fps / 70 ftIB from a single fill. Or turn it down more for more shots...
The Giffard's hammer mass/ hammer spring combo only provides a certain hammer force, it is suitable for opening the original cylinder valve against co2 pressure. (60 bar)
Any attempt to open the standard poppet valve against higher pressures would result in the valve opening less and less. Valve Lock.
To get around this valve opening issue, the new cylinder utilises a assisted valve, not a std poppet valve. The valve is biased so that it is easier for the Giffard hammer/ spring to open the valve at much higher pressures (ie 200 bar). So the Giffard hammer does not see the vastly increased pressure, however the air pressure is not regulated down to co2 levels, the full pressure flows along the transfer port to the bullet.
The new cylinder on air can develop significantly more power for a couple of reasons, the pressure seen by the projectile is a lot higher, the flow is better and air flows faster than co2."
Research on Giffard power settings.
With thanks to a Giffard owner for this chart:
My Giffard research is basically based on my desire to know when I was using full power, and when the extra gas used was wasted. I found what I called the "chuffing point" and this is where, after undoing the knurled thumbscrew that regulates power to a point at which the gun is safe. When it is screwed in again, firing every quarter of a turn, eventually the valve just opens enough to let a small quantity of carbon dioxide out, and the sound changes from a click, to a chuff.
At the chuffing point, the gun will not propell a ball, but it will indicate pretty nearly the second point the "point of minimum power" The knurled screw is wound in a 1/4 of a turn at a time, and when a ball is just ejected, this point is reached. One has to use a fresh ball each 1/4 turn to be accurate, and any ball stuck in the breech/barrel has to be fired out at higher power, remembering the position of the screw. A white mark in tippex is useful here.
When the point of minimum power is reached, maximum power is around a full turn of the screw from this, as indicated by my experiments (see photo) <b>The important thing is this: in each case, maximum power (defined as "minimum point of ball shattering") is quite some way from the screw being fully in. If I am right, allowing the hammer to drive the valve in further, by winding the screw in further just releases more gas than is needed.</b> After the ball has left the barrel, no amount of extra gas will increase its velocity, and the cartouch will be emptied more quickly. This is to be avoided. The 6m/m rifle that I owned shot exactly 100 times on full power - as the manufacturers claimed about 140 years ago!!
Article - Romance of the Carbona article plus addendum.
Article from Airgun Collector 3 by a Giffard enthusiast (see addendum at end):
An important addendum
January 2017 found me experimenting again with “things Giffard” and this time I wanted to revisit the valve washer issue. Washers of red polyurethane had been available to me for some time, and were virtually trouble free to fit and use, but I always had the feeling that the guns were underperforming. The 8m/m fusil would throw a ball with a good hard smack against the iron target, but would not smash it. I had (and still have) no idea of the valve material inside its cartouche since it was working when purchased and has not been open, but I have my suspicions. I will soon as it is due to be opened within a few days. I am betting it is red polyurethane! My attempts with nylon 6:6 as a harder material were not so successful. Nylon is hard, and unforgiving of any small imperfection in the valve at room temperature, and because it hardens as it is cooled, during re-filling it often would not seal. Clearly a material of hardness intermediate between nylon and polyurethane was needed. On 25th January I purchased some high-density polythene rod (HDPE is available in 20 and 30 mm and in BLACK) Valve washers made of this worked astoundingly well. Unlike the polyurethane, the stock could be turned, parted-off and lapped with no difficulty, and being black it looked like the original rubber. A cartouche so equipped was fitted to the 8m/m fusil with terrific results. The dimensions of successful valve washers were as follows:
hole/mm diameter/mm thickness/mm
fusil 10.0 25.9 – 26.0 5.0
pistolet 10.0 18.6 – 18.7 4.0
The HDPE valves have been performing completely satisfactorily and consistently for at least a month.
Another important issue is removing lost motion of the firing pin. This turns out to be more important than I considered previously. The valve must be set such that after the full blow of the hammer has fallen, there should be no lost motion of the pin, shown up as residual wobble in the hammer. This can be achieved to a certain extent by adjusting the thickness of the valve washer. Making this thinner brings the valve closer to the hammer, but the extent to which this can be done is clearly limited. If it is too thin, the valve will rest upon the central spigot in the centre of the cap, rendering sealing impossible.
Examination of the valve sometimes showed a considerable divot caused by repeated striking by the firing pin. This, if big enough, would always produce lost motion (as would a similar defect in the hammer where it strikes the back of the pin) An experiment with the 4.5m/m pistolet completely vindicated the idea that such lost motion must be obviated. The valve was cleaned, fluxed and a small piece of hard silver solder melted in using a blow-lamp heating from underneath. The idea was to fill in the divot, which was easily achieved. The silver solder, once polished, made a reasonable match with the brass of the valve. Once reassembled all lost motion was gone, and the previously slightly modest little pistol shot loud and hard, shattering ball at the iron target. It is interesting to note in this connection that the London Giffard cartouche has a valve with a steel centre.
These two issues are further revelations to me on the manner in which these gas guns were designed to work, and how they can be put back to work over 100 years after they were manufactured.