Fact or fiction?

[Turnup]

@ turnup:

"3) Fact from personal experience. In my youth. cautiously experimenting with deliberate dieseling using a Webly pistol. I found that, while it clearly increases MV, it greatly reduces accuracy. I stopped my experiments when the gun re-cocked. OK it does not take much to re-cock an old wobbly Webly pistol spring, but it surely did happen."




Maybe, if the weight faktor pellet-piston is matching. But how can a Weihrauch Barakuda then work safely?????????

OK, quick google reveals that the Barakuda is designed as a compression-ignition firearm. It works safely by being designed to be safe?????

[aimless]

OK, I know - , I have one; but ...... IF the pressure spreads out without determinded direction , it would NOT stop the forward moving piston and spring (with large kinetic energy) AND let him move backwards. And certainly not, because the pellet is already moving towards the muzzle......

I am quite sure, that there is NO planned diffussion/direction of the explosion by the BARAKUDA-rifle. Car-engines do have one....

So IMHO the piston (as described before) can not move backwards, if the mass-factor overrules the area-factor.

(My mass- and area-factors were taken from a vintage HW50 and without spring)

[Turnup]

OK, I know - , I have one; but ...... IF the pressure spreads out without determinded direction , it would NOT stop the forward moving piston and spring (with large kinetic energy) AND let him move backwards. And certainly not, because the pellet is already moving towards the muzzle......

I am quite sure, that there is NO planned diffussion/direction of the explosion by the BARAKUDA-rifle. Car-engines do have one....

So IMHO the piston (as described before) can not move backwards, if the mass-factor overrules the area-factor.

(My mass- and area-factors were taken from a vintage HW50 and without spring)

It is not correct to take the example of a firearm designed to use compression ignition, and generalise that to apply to a firearm not designed to be used in this way. I expect that the Barakuda has a heavy piston specifically to control piston bounce.

Note that tuners on here report that in normal operation, without dieseling some air guns exhibit piston bounce, that is where the piston is arrested and rebounds by air pressure alone. This is an effect which tuners try to eliminate. Now add dieseling into that and you can see that it is perfectly possible to move the piston backwards by a considerable amount. Note also that two posters on this thread report re-cocking has been found when deliberately inducing dieseling in guns not designed to do it.

Any dieseling event will be transitory (very fast by comparison to the moving parts of the gun). Once the very fast combustion has occurred, it will release combustion products (mostly gaseous)within the compression cylinder, and they will be much hotter, thus the pressure in there will be increased. It is this pressure which can push the piston backwards.

Within a diesel engine, controlling the propagation of combustion has nothing to do with directing a pressure wave towards the piston, the designers are trying to ensure that all parts of the fuel/air mixture are evenly ignited to promote complete burning. Ignition pressure waves will be of such short duration as to provide no meaningful force to the piston. It is the liberation of combustion gasses and heat which increases the pressure and moves the piston.

[aimless]

" Note that tuners on here report that in normal operation, without dieseling some air guns exhibit piston bounce, that is where the piston is arrested and rebounds by air pressure alone. "



so, if you close the muzzle completely, this would/should occur (every time)???
You invented a perpetuum-mobile

And that would be more than magic and worth a nobel-price

[shabee]

i knew this thread would get complicated
eric

[aimless]

Eric, NO: Interesting

And for me a challenge and a pleasure to improve my english

[Leonardj]

Thank you to all that have responded to the thread.
Now that everyone has shared their experience, it is my turn to weigh in on the three points in question based on my own experience.

1) Fiction. It is quite common knowledge that a freshly lube-tuned springer that is dieseling violently, to the point of achieving detonation, can be settled by shooting a few heavy pellets through it. Shooting the heavy pellets result in a much milder dieseling, which will slowly burn off any excess lubes in the compression chamber. After several heavy pellets, the mild dieseling ceases, and at that point, shooting the lighter pellets will no longer cause dieseling nor detonation. This practice that has been around for decades seems to directly contradict the theory presented in the first part of the noted statement.

2) Fiction. It is highly unlikley that an experienced airgunsmith would make a statement like that. I would be more inclined to expect some inexperienced wannabe to make such a claim in hopes of gaining some "cred". Yes, some abuses can appear readily apparent from the condition of the spring, but unless the suspected abuse can be verified by the owner of the gun, you are just guessing. For example, I had a Diana 34 in for repair, which had it's mainspring shattered into 6 pieces, with numerous fractures in the coils as well. I suspected dry firing as the cause. In speaking with the owner, I discovered that he had been using plastic, 3 grain pellets in the gun exclusively. IMO, that is about as close to dry firing the gun as you can get. The owner was advised on the best pellet weight to use in his freshly repaired gun going forward.

3) Fiction. I have had some guns in for repair that had some major damage due to detonation, and not one of the owners had experienced having the gun re-cock itself. Bulged compression chambers, front plug (complete with barrel still attached) blown completely out the end of the compression chamber, broken stocks, etc. Just to elaborate, dieseling is when there is a puff of smoke, of varying degrees, emitted upon firing, but if there is sufficient "fuel" and heat generated by the dieseling, then detonation is achieved - producing a very loud bang. It is the energy produced by that contained explosion in the compression chamber that is what causes the damage to the airgun.

[shabee]

Eric, NO: Interesting

And for me a challenge and a pleasure to improve my english

Good day aimless....its certainly had my attention and you are correct some of the answers have been "interesting " to say the least,
Your english is good enough, certainly better that would be my German, i take my hat off to you coming on and joining in despite the language barrier.
have a good day
eric