New project for 2021. Anyone guess what this is?

[DrGunn]

Wow, what a fantastic reproduction and a great looking pistol!

A video of same made by Matt will soon be available.

I could cobble together some sort of account of how it was made if it would be of any interest.

Cheers,

John

An account of its manufacture would be of great interest and I look forward to seeing the video.

[Binners]

'If it would be of interest'
You bet it will be of interest, great interest!

[micky2]

What a cracking job you have done there John. l take my hat off to you sir. l would say that is the best looking pistol that you have done so far.

[Leonardj]

John, the only thing that I can think to add to all the other comments is - Magnificent !

[Jerry Cornelius]

Remarkable. I have greatly enjoyed the earlier repros but how you could ever top this I can’t imagine

[Shed tuner]

that is very cool... my favourite of your projects thus far.

[Garvin]

OMG, it's beautiful! What an achievement! Just incredible. A lovely pistol by any reckoning, but such a close copy of the original (with 'engraving'!) is quite breathtaking.

[ccdjg]

Thanks for all the very kind comments. I must admit it is my favourite from a looks point of view. So I will put together a summary of the trials and tribulations of the project, but that will have to be in a separate post due to restrictions of number of pictures per post.

One thing that surprised me about this gun, and I don't know the explanation, is how it can develop quite a reasonable power from such a mechanism. It copes with heavy .25 darts quite adequately. The simple V-spring, which you can easily cock by hand, is compressed only about three quarters of an inch. When the gun is fired that short movement has to accelerate the hammer and piston unit shown below, which weighs a huge total of 160 grams. For comparison, the Webley Mark 1 piston weighs about 65 grams, and any attempts to increase its weight significantly reduces muzzle velocity.




So you would think that the acceleration of the piston would be too slow to effectively compress the air in the cylinder, and yet it does. I wonder if there is something inefficient about coil springs that we don't know about?

[Adam77K]

Wow that's excellent work! Make me a .177 PCP pistol in that form factor, that does about 3-4 ft.lbs, and I'll sell a kidney for it!

So you would think that the acceleration of the piston would be too slow to effectively compress the air in the cylinder, and yet it does. I wonder if there is something inefficient about coil springs that we don't know about?

I suspect it is operating only a little in what Cardew called the "popgun" phase of airgun power and mostly in the "blowpipe" phase.

So there's plenty of momentum behind the piston (low velocity but a fair amount of mass), but the start pressure of the dart is extremely low. So the air compresses a little, but almost immediately the dart starts moving. Then what you have is like a bellows. The big differential between the cylinder and barrel diameters means the air rushes down the barrel much faster than the piston is moving.

[Shed tuner]

also the total weight of the hammer assembly is not being accelerated, it it depends how far the mass is from the pivot pin.

[DrGunn]

So you would think that the acceleration of the piston would be too slow to effectively compress the air in the cylinder, and yet it does. I wonder if there is something inefficient about coil springs that we don't know about?

I think it may be that the geometry of the firing mechanism makes this system more effective - sort of like the cam mechanism used in compound bows.
In a conventional inline spring piston mechanism the force from the piston reaches a minimum at the end of the stroke when the air pressure reaches a maximum - only the momentum of the piston keeps it moving forward.
In this mechanism the geometry means the force on the piston is much more constant - the first half of the piston stroke where the pressure is lowest will use less than half the spring compression so there is more energy available for the second half where the air pressure is higher. Likewise the geometry of the mechanism means the angular momentum of the hammer will be converted into a relatively large linear force on the piston at the end of the stroke and so helping raise the pressure.
It would be interesting to work out the efficiency of this mechanism.

[ccdjg]

Both arguments are convincing, so I expect the answer is a combination of both effects. The relatively long barrel would make the most of the blowpipe effect, and the hammer lever arrangement is such that the beginning of the cocking stroke feels harder than the end of the stroke, so the analogy to the cam effect on a compound bow is a good one.

These pictures showing the cocking process might be informative:



Thanks,
John

[cringe]

Both arguments are convincing, so I expect the answer is a combination of both effects. The relatively long barrel would make the most of the blowpipe effect, and the hammer lever arrangement is such that the beginning of the cocking stroke feels harder than the end of the stroke, so the analogy to the cam effect on a compound bow is a good one.

These pictures showing the cocking process might be informative:



Thanks,
John

I agree, I think with this mechanism you would have stored [potential] energy in the hammer & piston, which when released would start the dart. then you have some back up of slower released energy which would speed up velocity ? so a longer barrel would make sense ?

[ccdjg]

It is interesting that the only commercialised airgun I am aware of that uses a hammer to cock the gun, also develops more poke than you would expect for such a light cocking effort. You can cock it just with your thumb, but it puts out BB's with a similar muzzle velocity to some BB pistols that are much harder to cock. That is the rare Healthways Plainsman Western (spring version, not the more commm CO2 version).

I stand corrected on this, but I think it is also the only airgun that stretches a coil spring when cocking, rather than compresses it.