Fact or fiction?

[Leonardj]

I spotted this statement on another forum and thought that it would be interesting to see how it compares with the experience of folks here.

"Using a heavier pellet will cause the pressure (and temperature) to spike higher and earlier in the shot cycle.... In a gun that is marginal on dieseling, this increase in pressure and temperature can cause dieseling to occur.... There have been reports by reputable airgunsmiths that they can tell by "one look" at the spring if the gun was shot with too heavy a pellet from the damage to the spring....that the dieseling can be so violent as to even re-cock the piston...".

We'll break it down into three parts since there are three distinct points being made by that statement.

1)

"Using a heavier pellet will cause the pressure (and temperature) to spike higher and earlier in the shot cycle.... In a gun that is marginal on dieseling, this increase in pressure and temperature can cause dieseling to occur".

Fact or Fiction?

2)

"There have been reports by reputable airgunsmiths that they can tell by "one look" at the spring if the gun was shot with too heavy a pellet from the damage to the spring".

Fact or fiction?

3)

"that the dieseling can be so violent as to even re-cock the piston".

Fact or fiction?

[Josie & John]

Hi Len,

I think Jim Tyler and the late Mike Wright looked into this and you may get more response if you post this in the General Airgun section, on the basis more 'experimenters' frequent that section than this one.

I almost experienced point 3 years ago when I broke the piston rod on a Webley Ranger due to heavy recoil. The rifle didn't quite cock itself but came close!

Kind regards,

John

[larrylamppost]

1)don't know
2)i doubt it
3)it has happened

[Muskett]

Its works on the same principal as a Fire piston.
https://www.youtube.com/watch?v=sgKWwGv6y-E

However, to cause an explosion there needs to be fuel.

A tighter pellet, or heavier pellet will increase the pressure and so more heat. If that is enough to ignite anything in a particular gun is another matter.

Some idiots have put drops of lighter fuel to make an explosion happen, in order to get more power! Other potions and oils might be able to do it too.

If the explosion is big and violent enough then sure the gas has got to expand and go somewhere; so anything is possible. Same principle as a blowback firearm.

A big enough explosion is unlikely to be obvious at looking at the spring but a blown cylinder, enlarged chamber, might be; especially as some are made of mild steel and not that thick.

So its all possible.

A more experienced gunsmith might be more able to prove the theory having come across examples. I think its highly possible with some of the pyromaniacs I've come across; boys and their toys

[Garvin]

Len, as I said over one the AVA, speaking strictly as a layman in terms of technical knowledge, I strongly suspect 2) and 3) are fiction.

The pressure needed to recock the gun after the pellet was expelled at supersonic speed would have to be powder-burner massive, surely?!

And the airgunsmith who can take "one look"? Maybe, but they'd be foolish not to consider the other options too, wouldn't they?!

Or am I just plain wrong?

[aimless]

1) quite sure: yes
2)???
3)no, the pressure/explosion would take the easier way "out" (thru the barrel), because the pellet is lighter than the piston (disregarding the spring)

ps: to 1) : "using a (very) much heavier pellet"

[magicesperanto]

1) Highly plausible.

2) Highly unlikely.

3) Tosh in my view, if that much force was involved in dieseling, surely the world would be littered with cheapo airguns with exploded chambers?

[johnbaz]

But Larry lamppost said that #3 had happened so he must have first hand knowlege that it's possible


John

[shabee]

1. fact.
2. fact in so much that there probably will be an airgun smith that makes this claim, but entirely fiction in reality, there could be no way of knowing that a heavy pellet had actually caused the damage, any dieseling caused by a heavy pellet in a marginal gun would be insignificant, and only very mild, and unlikely to cause any damage.
3. fact.
eric

[magicesperanto]

But Larry lamppost said that #3 had happened so he must have first hand knowlege that it's possible


John

I can see it being possible with a completely blocked barrel, but a tight/heavy pellet?

[aimless]

#3 IMHO impossible according to the "momentum conservation law" if both ends of the "combustion chamber " are movable and the heavier part (piston) shall move....but I admit, I have to take my calculator now out to calculate with he pressure regarding the area.......

[aimless]

OK:

area of pellet : ( .177) 16 mm² weight: 0,5 g
area of piston: (diameter 30 mm) 706 mm² weight : 253 g

factor of weigth piston/pellet: 506

factor of area piston/pellet: 44

so the bigger area of the piston (model of the combustion chamber , both ends -piston-pellet- open/movable)
can not "overrule" (produce a higher force) the lower weight of the pellet in the first moment of "explosion" . so the piston will not move.

or am I wrong?

please excuse my humble technical english....

[Turnup]

1) Fact.

2) While it is possible to visually identify spring damage, I find it hard to accept that the damage is characteristic of one cause only. Also note that dieseling can be caused with light pellets, so how can you tell?


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.

To the posters who reason that a light pellet will give way before a heavy piston, note that compression tube pressures act equally in all directions, and that the larger area of the piston will will therefore cause the piston to experience more force than the pellet. Also the pressure in the barrel will in fact be lower since there is restriction in flow at the breech, and also possible sonic shockwaves there too. It is clear that even without dieseling, piston rebound can occur (many of the tuners on here will attest to that) - the rest is a matter of extent.

[Leonardj]

I think Jim Tyler and the late Mike Wright looked into this and you may get more response if you post this in the General Airgun section, on the basis more 'experimenters' frequent that section than this one

Thanks John, done.

[Leonardj]

Some interesting responses thus far.
Keep 'em coming.