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

[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.

[aimless]

@ 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?????????

[duomatic410]

Gun can recock on fireing? YES. Have had it happen on Webley mk3 in 177, and have had cocking rods broken.
This was caused by dieseling(on purpose for power) using aero fuel😐.
(65 years ago).

Springs finish up totally kna..red, a new spring will look like one that's been in years when it it's been in weeks.

Heavy tight pellets will put the pressure up when dieseling, and can cause it to diesle when it perhaps it wouldn't useing a light pellet.

And if you have a mk3 or other air rifle that doesn't seem to reach power as it should, there is a chance that your cylinder as bulged due to the above.

[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?????

[trick cyclist]

The physics can only answer so much - if we take a 'snapshot in time', where the pellet is moving up the barrel, and the piston is still reaching (or has reached) the very end of its travel, then using the simple formula of Pressure (P) = Force (F) / Area (A), we can see that by having to make the assumption that P is the same everywhere in the barrel/breech (as Turnup said), the force on the pellet will be clearly many magnitudes greater than the force on the piston. However, P=F/A only really works for static systems, and as Jim Tyler and others who really study this will say, the springer firing cycle is so complicated, it is very hard to truly calculate what is happening at any one time in such a dynamic environment, soooo, in the case of a piston that is approaching the end of its travel, with the air temperature now at several hundreds of degrees, a detonation at the piston face could conceivably produce a shockwave that flings it back up the compression tube. I'm in, though I've never seen it!

[MarcDV]

Interesting propositions. My take on the claims:

1) Since the pressure is purely a function of the barrel bore and the distance traveled, the pressure (and therefore the temperature) must be the same regardless of pellet weight. There are several contributory issues not addressed here, such as pellet acceleration and final velocity, pellet fit, residual lubrication and friction, neglect these (very minor side effects) and this is a non-starter.
2) Invalid, see response above.
3) A guess at best. While it is highly likely that dieseling caused many a spring failure and also theoretically possible for the spring to re-cock, in 45 years of handling air guns, I have never seen this.

Good stuff to keep our grey matter churning!

Marc.

[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