Omer quitting Pneumatic Spearguns

[popgun pete]

I just find this image regarding bumps on Cyrano piston. I actually find the piston itself too among my Cyrano parts. I had modified it to make hydro damper with it so the modified piston was without bumps. But now I am sure the bumps on Cyrano piston are inside diameter of 8 mm and the bumps do not get in contact with the anvil of shock absorber. The OD of the grove in the anvil is 10,8 mm, same as the piston OD. The depth is about 2 mm and the boring throught it is 8,8 mm. Bumps on Cyrano piston may serve for additional centering of the piston in contact with the shock absorber.

View attachment 59296

I have looked down the muzzle of both my Cyrano and Sten guns and could see the ring of small bumps, if I can see them then they are not sitting on the face of the anvil.

 

[tromic]

I have looked down the muzzle of both my Cyrano and Sten guns and could see the ring of small bumps, if I can see them then they are not sitting on the face of the anvil.

Yes, I think so.

 

[tromic]

The bumps on the Mares piston nose don't sit on the anvil, they are in the bore area and are thought to be locating features with respect to the bore alignment. They are well inside the bore however, so they don't really do that.
View attachment 59290
That is daylight you can see through the gap, this gun is under full charge pressure with the piston pressing against the anvil face and sitting on a ring of bumps. The bumps need to be sanded off or the piston refaced in a lathe to make it flat and spread the contact pressure between piston nose and anvil. Otherwise you will crack the gun's shock absorber anvil after enough shots are put through your gun.

Regarding Omer piston, as on image above, I was thinking about what was the intension to make those bumps at the front face of the piston. Because of that in water barrel gun the water in front of the piston would have two times higher speed of water toward water escaping ports. Two times higher speed means four times higher kinetic energy of water then it would be with piston without bums. For that amount of energy shock absorber should work less. So it is maybe helpful in water barrel gun..? But in vacuum barrel gun it would be devastating for the shock absorber and the piston because the contact surface of impact would be two times smaller..