Exploding moderator !!!!

Crow Man

Well-Known Member
Yesterday my friend was checking the zero on his HMR, first shot struck around an inch high, second slightly lower, third shot around the same. Then about a second after the third shot there was a LOUD explosion, and this was the result. Any thoughts?
 

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Crow Man

Well-Known Member
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The internal core/baffle stack is still in place screwed on the end of the barrel. You can see a pressure bulge just in front of the grub screw. The moderator exploded after the third shot. The core can just be screwed off as normal, no damage to the threads.
 
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User00001

Well-Known Member
Pretty standard exploding HMR, at least this setup had the decency to let go at the end farthest away from the firer rather than the standard chamber/magazine well/barrel. God knows why the HSE haven't jumped all over this by now.
 

Crow Man

Well-Known Member
Pretty standard exploding HMR, at least this setup had the decency to let go at the end farthest away from the firer rather than the standard chamber/magazine well/barrel. God knows why the HSE haven't jumped all over this by now.

It's not a bullet lodge in the barrel and then fired again explosion. The explosion happened inside the mod a second after I saw the third round strike the target.
 

User00001

Well-Known Member
All fine & dandy but given the 'event' occurred at the projectile exit point my money is on that end of engineering chain.

K

Your probably right but I'm afraid it still adds to the long list of incidents related to this calibre even if only by coincidence in this case.
 

ashray

Well-Known Member
oil in the moderator ,first and second bullet heated the oil into vapour third shot set it off! ask your friend how he cleaned his mod.
 

Crow Man

Well-Known Member
oil in the moderator ,first and second bullet heated the oil into vapour third shot set it off! ask your friend how he cleaned his mod.
That was my thought, he said he hasn’t used any oil/cleaning fluids on the mod, the only thing he did was a slight amount of copper grease on the thread.
He seems to think it could be a build up of un burnt powder residue. Can’t see that myself.
 

Tom D

Well-Known Member
Here’s my theory: the problem with HMR ammo has always been split cases from poor annealing. The splits are often invisible but they do allow moisture to get into the rounds. Sometimes these damp rounds don’t fire at all, sometimes they only achieve partial combustion and the bullet gets lodged in the barrel. In this case I think poor combustion has left unburned powder in the mod which may have been building up for a while. This has ignited and caused the mod case to fly back with sufficient force to split the forend. I don’t think a bullet-baffle strike could have done this.
 

Cottis

Well-Known Member
What mod is/was it?
How often was it cleaned?
How many shots has it seen in its life?

They are are a consumable and HMR mods often get neglected yet they suffer from a build of crud from that nasty powder they use. The residue is grim and also seems to get pasty and wet. Not sure what the internals of the mod are made of but I have seen some cheapo ones fail.

Guessing a build up of gas somehow due to crud build up not allowing gas to escape properly after successive shots and then some sort of mini explosion happening. Very odd but something has happened post firing.

Glad nobody was hurt. Time for a new stock and mod though. I really rate the Wildcat Panthers for .17's
 

jb1

Well-Known Member
My bet would be unburnt powder, had a sak woosssshhhh like a firework years ago. It seemed to be a spurious fault night time lamping was exiting when it happened.

I'd Put money on that it's down to rubbish ammunition. Mods are designed to take pressure beyond the pressure created by HMR rounds (although some have been know to fail) and doubt it's the crud that's the cause.
 

M Smith

Member
My bet would be unburnt powder, had a sak woosssshhhh like a firework years ago. It seemed to be a spurious fault night time lamping was exiting when it happened.

I'd Put money on that it's down to rubbish ammunition. Mods are designed to take pressure beyond the pressure created by HMR rounds (although some have been know to fail) and doubt it's the crud that's the cause.


I witnessed a similar event with a sak moderator on a HMR, assumed it was ignition of unburnt powder. We checked the barrel was clear and stripped the mod before any more rounds fired.

I started cleaning my sak more regularly after that.
 

Crow Man

Well-Known Member
I witnessed a similar event with a sak moderator on a HMR, assumed it was ignition of unburnt powder. We checked the barrel was clear and stripped the mod before any more rounds fired.

I started cleaning my sak more regularly after that.

I don’t think this one will need much stripping down. :D
 

kennyc

Well-Known Member
It's an early DM80, I have the same mod on my .22H, it's done a lot of work with no issues and gets cleaned rarely
the Hornet probably burns all the powder, rimfires are notoriously poor on total combustion, if I remember correctly there was an anouncement a few years ago advising that CF mods shouldn't be used with rimfires due to the possible explosion hazard due to accumulation of unburnt powder in a mod.Cleaning is the key.
 

Edinburgh Rifles

Well-Known Member
unburned powder or not

its a propellant not an explosive
you could fill the ****er with fresh powder and light it and it won't pop like that

it requires the sealed cartridge to generate pressure
You'll get the firework effect as described above but not a pop

As pressure acts universally on all surfaces I am trying to work out how the jacket has had enough linear force on it to unseat the grub screw and slide a sleeve over the baffle arrangement.

I would suggest the screw has been loose and the seal at the front has not been entire allowing partial gas escape and creation of a linear force
 

25 Sharps

Well-Known Member
the Hornet probably burns all the powder, rimfires are notoriously poor on total combustion, if I remember correctly there was an anouncement a few years ago advising that CF mods shouldn't be used with rimfires due to the possible explosion hazard due to accumulation of unburnt powder in a mod.Cleaning is the key.

That would be the flame you see coming out of the end.

I never clean my rimmie mod's and have never had one explode.
 
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