Me again and my crazy ideas

[Diablero]

Have any of you guys used 9mm + shafts on your Cyranos, or similar 11mm barrel guns, or more than 10mm shafts in your 13mm barrel guns?

Disadvantages besides lower shaft speed?

Im in the process of making some 9mm shaft for my cyrano and a 10mm shaft for my Mares Pipin 130. The idea is to have them running on dry barrels, (tovarich or similar).

Any comments suggestions are welcome.

Thanks

Juan Carlos

 

[DivingDane]

why so heavy? i've never met a fish where and 8mm sprung steel shaft wouldnt do the job plus like you said they are alot faster, short answer is of all the pneumatics sold in northern australia (quite alot) i am yet to see one with such heavy shafts.

DD

 

[Diablero]

Hi Dane
Im making a couple experiments with them, in theory a mares cyrano 970 holds aprox 41.15 ml of water when charged with a 7mm shaft. With a 9mm shaft it should hold only 20.5 ml of water, this with some good openings in the front muzzle should help exit the water better and maybe the speed lost from weight could be compensated by this. If the 9mm shaft goes as fast or not too much slower I would be more than happy.
If the vaccum or dry barrel mod its done, then it should retain at least the same speed of the 7mm shaft.
All this its just theory, but I want to try and compare, just wanted to know if somebody did it before or not.

Besides Im trying to suit the Mares 130 for Tuna and Marlin, I know its not made for this but maybe with a couple of mods I can get it too shoot faster and further.

Thanks again

 

[tromic]

If with 7 mm shaft you have shaft speed 34 m/sec than with 8 mm shaft you would have 29 m/sec and with 9 mm shaft only 26 m/sec. Bad idea, even with dry barrel.

 

[popgun pete]

Shooting a heavier shaft will result in more recoil, so that is another thing to consider.

 

[Diablero]

Hi tromic
Were did you get this numbers from?
Are there any comparisons charts of dry vs wet barrel velocities?
How much m/sec are gained from a standard wet barrel to a dry barrel mod?


Thanks

If with 7 mm shaft you have shaft speed 34 m/sec than with 8 mm shaft you would have 29 m/sec and with 9 mm shaft only 26 m/sec. Bad idea, even with dry barrel.

 

[Diablero]

Hi Pete
I was waiting for your comments on this.
Yes I know there will be more recoil as tha shafts are heavier, but if theres a significant increase in velocity, I could live with that.

Thanks
JC

Shooting a heavier shaft will result in more recoil, so that is another thing to consider.

 

[tromic]

Diablero, I made some calculations. look at the video here: http://forums.deeperblue.com/pnumatic-spearguns/81902-vacuum-barrels-aka-dry-barrels-2.html
I had not seen significant difference with dry barrel.

 

[Diablero]

If theres no velocity increase doing a dry barrel upgrade, then whats the point?

For me the 3 main reasons for doing this upgrade were

1. higher velocities at same pressure
2. lower noise
3. less wear of parts (when pressure is reduced)

I dont care too much about 2 or 3 but 1 was very important.
Are you sure youre not getting the barrel flooded?

 

[popgun pete]

Some older pneumatic spearguns used a 9 mm shaft, but they relied on the momentum of a slow but heavy shaft to skewer their unsuspecting target fish. One example is the mid-sixties Technisub "Jaguar"; I am thinking more of the longer one rather than the smaller "Cub" or "Piccolo" version. To drive a 9 mm shaft at higher speeds underwater you need a lot of gun power and that requires a gun with very high air pressure in it, maybe 45 Bar or more. Such a gun will be a challenge to shoot unless the gun is ballasted in some way, plus there is the "small" problem of loading it at that sort of pressure.

Using the bulk of the shaft as a means to minimise water in the gun's inner barrel is not a good idea, you will still only have the same air pressure driving the shaft in the gun. If you go to the dry barrel option then you will effectively gain some propulsive force by virtue of eliminating most of the back pressure in front of the advancing piston, but you will then be asking it to drive a heavier shaft. The same gun using a dry barrel and an 8 mm shaft will perform better as there is less mass to accelerate, a 9 mm shaft being considerably heavier than a 8 mm shaft. However if your target is at long range and unlikely to move then a heavier shaft will slam into it with considerable momentum due to its sheer weight, the speed of a lighter shaft will have washed off and it will have less momentum and penetrating capability at that distance. So it boils down to the situation and type of fish that you are going to shoot and where you are aiming for, bodies being softer than heads.

I just tried putting my old "Jaguar" shaft in my "Sten", the spear tail goes through the muzzle OK, so it will swallow a shaft with a 10 mm stop diameter at the rear end. I think you would be better to consider using a dry barrel kit on your Sten 130 and stick with the 8 mm diameter shaft. Filling the space around the spear with air or a partial vacuum rather than metal is the best way to go, especially with the lightweight Italian pneumatic spearguns.

 

[tromic]

If theres no velocity increase doing a dry barrel upgrade, then whats the point?

For me the 3 main reasons for doing this upgrade were

1. higher velocities at same pressure
2. lower noise
3. less wear of parts (when pressure is reduced)

I dont care too much about 2 or 3 but 1 was very important.
Are you sure youre not getting the barrel flooded?

1. Yes higher velocities, but not significant if the gun is well constructed.
2. Agree, obvious from the video.
3. I would say less wear because less/no salt water is in the barrel
4. I noticed some higher recoil
5. It is more difficult to load the gun at the same pressure.

I made some minor improvement with tomba so I expect some higher speed of the shaft than at the video.
I agree about what popgunpete told. It would be better to consider Sten 130 instead of the Cyrano, with 8 mm shaft.