Me again and my crazy ideas

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

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.

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

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.

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.

Diablero said:

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?

Click to expand...

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.