1000+ FPS 8mm Giffard HPA conversion

[Buxton]

http://fbcdn-sphotos-a-a.akamaihd.ne...08146982_n.jpg

Earlier this month I made myself a new cylinder for the Giffard. The original cylinder is in good condition and holds CO2 perfectly fine. But for everyday plinking, I figured I would convert the Giffard to HPA.
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My Giffard will shoot the 8mm, 49grain ball at around 600fps producing around 40 Ftib at the muzzle on co2. Perfectly adequate 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.


It’s a real hoot to shoot

Chris

http://fbcdn-sphotos-e-a.akamaihd.ne...93485490_n.jpg

[junglie]

That sounds great fun! Are these exempt from FAC because of age, or have you got it on ticket? Bet it does go through an old metal dustbin at full power! I'm impressed.

[Tantomurata]

That sounds great fun! Are these exempt from FAC because of age, or have you got it on ticket? Bet it does go through an old metal dustbin at full power! I'm impressed.

Antiques are only exempt under Section 58(2) if held as a Curiosity or Ornament. If there is any intent to use an antique gun it ceases to be afforded the exemption offered under Section 58(2) and becomes subject to relevant licence.

[albrown]

blah bah blah... let the Legal Eagles above argue over the Law elsewhere.

I would just like to say thank you for posting such an interesting gun and talking about your modifications..

I have always wondered about the performance of these old guns and you have allowed a glimpse at that.
Cheers
Alex

[Buxton]

Yes its on ticket for shooting. Don't know about old metal bin penetration tests, but it shatters the balls into fragments. At over 100FTIB its more than capable of some damage.

The performance from old Giffards is great, with a telescopic sight mounted I can put up some cracking groups.


Hey Eric, did'nt realise you are just up the road.

[junglie]

Yes its on ticket for shooting. Don't know about old metal bin penetration tests, but it shatters the balls into fragments. At over 100FTIB its more than capable of some damage.

The performance from old Giffards is great, with a telescopic sight mounted I can put up some cracking groups.


Hey Eric, did'nt realise you are just up the road.

I was curious about the fac status & pleased to see such a nice old gun being actually used! The dustbin quip was tonque in cheek. Well out of my price range owning one but thanks for an interesting post,wonder what the accuracy would be like with a good custom slug molded bullet?

[Tantomurata]

blah bah blah... let the Legal Eagles above argue over the Law elsewhere.

Junglie asked a question, both Eric and myself replied. We both said the same thing, that's not arguing, it's simply answering Junglie's question with factual answers.

[Herpquest]

Even though a Giffard is now classed as an antique and can be kept by a collector as part of a collection without a FAC, when used as a rifle and not just as a 'show piece' a FAC has to be in force.

NB. Sorry George, I hadn't seen your post when I posted this.
Eric