Loud 1st shot?

[jthyttin]

And somehow magically there’s no oxygen on subsequent shots?

Yes because oxygen (fresh air) is replaced by combustion gases, and there's nothing to drive the gases out and replace them with fresh air.

It's very well known phenomenon, and in some cases moderator is flushed with e.g. nitrogen and sealed (for duration of, let's say max few hours). FRP itself is usually a matter of single minutes.

Other related phenomenon is "shooting wet", i.e. intentionally putting water or some other substance in the mod. There are even special products for this, and the effect stays for a number of shots. Sometimes it's used in place of the nitrogen purge. Usually these are for pistol calibers, wet mod might create dangerous situation in usual rifle chamberings.

 

[Liveonce]

all I can say in 49 years of shooting a .22lr I have never experienced this once on the first shot.

To the OP try a different moderator.

Millions of rounds of .22lr subsonic are shot every year so it should be a common occurrence then

Don’t believe the oxygen idea for one second, the air we breathe is 21% oxygen, which is insufficient to be an explosive mixture, what chemical process could possibly be occurring inside a mod to generate the level of oxygen to that required to go pop at the exact millisecond you fire the rifle for the first shot but no subsequent shot and why not every first shot?

 

[old keeper]

Giving this a bit more thought, like many other .22 users, until Winchester in particular changed to their 42 grain ammo, I never remember getting the occasional loud report. And that's over decades of use. Certainly, "first round pop" is something I've never experienced.

 

[sir-lamp-alot]

Do you oil the moderator and leave oil behind?

No literally never clean the .22lr unless it gets wet

 

[HonestJohn]

This is generally experienced with moderated 22lr subs only. Whilst it probably happens more than you realise, it’s still not loud enough to make people notice it.

…they say the supernatural isn’t supposed to happen..,but it does happen

 

[Taff]

Attenuation changes after first shot as gasses are left in mod ?

Correct, if using k baffles apparently

 

[Mungo]

View attachment 421515

Not convinced.

It may well have something to do with the gas mix changing or combustion gasses being left behind. But to suggest that there’s no oxygen in a mod after the first shot is just implausible.

 

[HonestJohn]

Going to crack one off in the garden. Will let you know how it goes

22lr that is!

 

[dogman56]

I've had this with Winchester subs and now never use them, no issies with CCI or Eley subs

 

[NoIDeer]

Don’t believe the oxygen idea for one second, the air we breathe is 21% oxygen

Pondering this statement, back of a fag packet physics/maths, the muzzle pressure of a 22lr could be around 75 bar which would give you an approximate oxygen partial pressure of around 15 bar. Plenty for a pop with unburnt propellant.

 

[Liveonce]

Pondering this statement, back of a fag packet physics/maths, the muzzle pressure of a 22lr could be around 75 bar which would give you an approximate oxygen partial pressure of around 15 bar. Plenty for a pop with unburnt propellant.

more likely to get a dieseling type pop if oil in the mod then from unburnt powder present in a .22lr mod, plus powder only burns if unconfined, lose as it would be in a mod.
Oxygen is not flammable but an oxidiser so it would only aid any burning powder, if it was exploding then surly we would see mods getting damaged. Oxygen is also heavier than air and would be very unlikely to accumulate in a mod.

Oxygen from a welding cylinder can spontaneously ignite oily rags and is/was warned about as part of the risk if using the cylinders.

OP are you storing the rifle with the mod on or off, barrel down or up.

 

[sir-lamp-alot]

OP are you storing the rifle with the mod on or off, barrel down or up.

mod on, muzzle up

 

[Dunwaters]

If the first shot hits what’s the problem?
Much better than a quiet miss.

 

[Apthorpe]

Pondering this statement, back of a fag packet physics/maths, the muzzle pressure of a 22lr could be around 75 bar which would give you an approximate oxygen partial pressure of around 15 bar. Plenty for a pop with unburnt propellant.

I find this unpersuasive. I'm not clear why the muzzle pressure of the .22LR would be the same as the pressure inside the moderator. One wpuld necessarily expect that to be much lower for several reasons.
Secondly, I'm not persuaded that unburnt propellant requires oxygen. Propellants are designed to combust completely in the absence of oxygen. To the extent that spme propellant hadn't completely combusted (which i think highly unlikely in a round like .22LR, then it would combust in the moderator independently of the presence or not of atmospheric oxygen.

 

[NoIDeer]

I find this unpersuasive. I'm not clear why the muzzle pressure of the .22LR would be the same as the pressure inside the moderator. One wpuld necessarily expect that to be much lower for several reasons.
Secondly, I'm not persuaded that unburnt propellant requires oxygen. Propellants are designed to combust completely in the absence of oxygen. To the extent that spme propellant hadn't completely combusted (which i think highly unlikely in a round like .22LR, then it would combust in the moderator independently of the presence or not of atmospheric oxygen.

I think I agree, @Liveonce above is probably on the money with dieseling. The raised pressure of oxygen would help with the "pop".

 

[Smellydog]

I'd just scrap that mod....