Moisture vs Chamber Pressure

[Tribe]

<span style="text-decoration: line-through">Will altitude or I guess, air density affect chamber pressure? Not talking Temp....</span>

....ok so definitely not Altitude/air pressure....

Pressure spikes do to moisture on ammo / in chamber.... tips/tricks?

 

[Lindy]

Re: Altitude vs Chamber Pressure

No. Powder contains its own oxidizer. Guns will fire underwater.

 

[Greg Langelius *]

Re: Altitude vs Chamber Pressure

...or in space, and a lot safer, too.

I'd hate to think about the chamber pressures being developed when the propellant needs to push out a column of water besides the bullet's mass. While not negligible, the mass of the air column in the bore is comparatively so, and air is compressible.

Greg

 

[Tribe]

Re: Altitude vs Chamber Pressure

Would water in the chamber create a pressure spike?

I ask, because the last couple of times i've been in wet conditions, where ammo and chamber were wet, I've experienced signs of increased pressure. May have just been coincidence, but it's proving to be a consistent coincidence....

 

[Lindy]

Re: Altitude vs Chamber Pressure

Yes, it can. What happens is that the water in the chamber occupies volume, which reduces the room for the case to expand under pressure. Water is <span style="font-style: italic">relatively</span> incompressible, and that creates an increase in pressure.

It's best to keep water off your ammo and out of the chamber if possible.

I picked up a trick from shooters at the Bisley range in Britain. You've probably heard it rains there...

They take a piece of naugahyde or similar material, and attach it to the left side of the receiver. Then they drape it over the scope, covering the ejection port, but still allowing access for scope adjustments and bolt manipulation.

In any case, a dry chamber and ammo will make your rifle happier.

 

[Greg Langelius *]

Re: Altitude vs Chamber Pressure

Yes, it can and has done so in my experience.

There were times when I was dealing with high local temps and pressure spikes, so I placed my ammo in a cooler until I was ready to shoot. Neglecting to notice condensation, I had several rounds blow primers anyway, then realized I was putting wet ammo into the chamber.

Apparently, propellant combustion heat and pressure converts the water into high temeprature, high rpessure, steam; and this can also apparently create significant pressure spikes.

Greg

 

[Lindy]

Re: Altitude vs Chamber Pressure

I suspect that phenomenum - which I've seen as well - is more a straight volume reduction in the chamber size. Limiting the size the case can expand to under pressure must effectively cause in increase in pressure, just as a lower case volume would - and does.

If the case really got hot enough to convert that water to steam before the bullet left the bore, you wouldn't be able to touch fired cases.

 

[acehigh]

Re: Altitude vs Chamber Pressure

the last case I tried to pick up outta my Barrett coulda boiled water I think. It was hot.

JH

 

[Greg Langelius *]

Re: Altitude vs Chamber Pressure

Lindy, you could be right.

However, I also have a friend who refuses to shoot to my right side anymore, after getting a burn on his neck from a case my M1A ejected.

Of course, I no longer have the M1A anymore, and I haven't seen the friend since the last time I shot the Carlos, now several years ago.

Greg

 

[Fuzzball]

Re: Altitude vs Chamber Pressure

The larger problem of firing a gun underwater is the weight of the water in the barrel adds to the weight of the bullet. Together they have a LOT of resistance to acceleration/movement so the chamber pressure can get VERY high.

SCUBA divers do fire cartridges underwater against some fish but they use short, loosely fitted barrels so the chamber pressure won't become unsafe. And, in some designs, the blasted-out water colume itself does more tissue damage to the critter than the bullet.

 

[MitchAlsup]

Re: Altitude vs Chamber Pressure

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Tribe</div><div class="ubbcode-body">Will altitude or I guess, air density affect chamber pressure? </div></div>

Consider that the maximum variation of air pressure is on the order of 3 PSI (at a given altitude) and maybe 7 PSI over the altitudes that humans live.

Now compare this 7 PSI to the 58,000 PSI of the burning powder in the chamber and come to your own conclusions.

In my opinion, there may be some other effects that interact with chamber pressure, but pure altitude is not one of them.

 

[Tribe]

Re: Altitude vs Chamber Pressure

Thanks all.... it's definitely the moisture on the cartridge...

Thanks for the tip Lindy... it rains a bit out here in the great Northwet as well.

 

[The Mechanic]

Re: Altitude vs Chamber Pressure

I was wondering if the water could also act like a lubricant when fired. This could let the case push back harder than normal instead of getting its grip from the chamber. There was a thread discussion a while back about lubrication left on cases.

 

[dontstrokeme]

Re: Altitude vs Chamber Pressure

Saw this verified today as well!!!

This was the first on the google search Tribe!

My thinking is that when the bullet is fired the brass swells to the chamber dimension, then returns to close to it's "ready to fire" dimensions. Brass is elastic...that is why we use it.

When the water is in between the brass and the chamber the water blocks the brass' movement and the brass has to move somewhere so it goes back, and into the ejector hole.


I wiped my rounds off with an absorbant "paper towel" type rag and still got over pressure. It did seem to get increasingly worse as the day and rain progressed!!!

 

[Tribe]

Re: Altitude vs Chamber Pressure

Yeah dude.... I actually just pulled 100 bullets.... working on a tamer load tomorrow, in hopes of a "weather proof" solution....

My fear is, I'll be wasting my time... I'm wondering if anyone can confirm or deny, that a mellow load will be more forgiving in adverse situations, or if you have moisture in your chamber, you are just f*$%@#, regardless of how close to the edge you run your load......???

Out hear in the Great North Wet... not even the Sham-Wow can keep that chamber dry.....

 

[ranger1183]

Re: Altitude vs Chamber Pressure

Now there's an idea. Tactical Sham-Wow chamber apron!

 

[Tribe]

Re: Altitude vs Chamber Pressure

DSM was already planing on putting a call in to Stu!

 

[Tribe]

Re: Altitude vs Chamber Pressure

Can you get Sham-Wow's in Multi-Cam??????

 

[MitchAlsup]

Re: Altitude vs Chamber Pressure

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Greg Langelius *</div><div class="ubbcode-body">...or in space, and a lot safer, </div></div>

Question: do you need the extra thick helmet shield when firing the 50 BMG with a brake in space?

 

[ranger1183]

Re: Altitude vs Chamber Pressure

Here is a question and Lindy's excellent answer regarding "Shooting in a down pour".

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Question (editted for personal info):

Lindy,

A buddy of mine was shooting in a practice for a tactical match. The heavens really opened up and everything was soaked. He was not able to keep either his ammo or chamber dry.

His reloads which were specifically loaded for long range accuracy began to blow primers. Those loads were still very accurate, but obviously at much higher chamber pressures.

He has asked me <span style="color: #FF0000">if a milder load would be the answer to not blowing primers - or - will he always have overpressure problems when shooting in a downpour?</span> Waiting for a sunny day is not a viable option as he live in the Pacific Northwest where the rainy season is from 1 Jan to 31 Dec.

His rifle is a 300 Win Mag AI AWSM.

Any help would be greatly appreciated.

Thanks!


<span style="font-weight: bold"><span style="color: #000099">Lindy's Most Excellent answer</span></span>(Key point I was looking for is highlighted in red):

If your ammo and chamber are wet, you're going to have pressure problems. The reason is that water is relatively incompressible, so any water on the ammo and in the chamber takes up space that is not available for the case to expand into.

Less space - more pressure.

<span style="color: #FF0000"><span style="font-weight: bold">Loading down is not the solution. The only solution is to keep your ammo and chamber dry.</span></span>

Shooter's at Bisley in the U.K., where it rains a lot, often tape a piece of Naughahyde or similar heavy waterproof material to the left side of their receiver, then drape it to the right over the scope, sheilding the ejection port from the rain, but still allowing them to reach up under the fabric to manipulate the bolt. And keep the ammo out of the rain.

In combat, of course, you shoot when you have to.

Regards,
-- Lindy


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I hope this helps out!

 

[dontstrokeme]

Re: Altitude vs Chamber Pressure

Yeah I belive dryness is the answer but I had my rounds in a plastic ziploc bag....and dryed the mag off, covered the scope/action with a Rivers West Boonie when not in use and wiped the rounds really well....but my fingers were wet so even that amount of water seemed to cause the higher pressure and I was getting inconsistant shooting with a load that normally works very consistant. Being as we aren't real snipers and didn't HAVE to shoot I called it a day. But I am wondering what people actually use to keep their rounds dry in "snipershide.com" shooting situations....meaning the field shooting that we normally do....might be a thread for the fieldcraft section!!

 

[ranger1183]

Re: Altitude vs Chamber Pressure

Joe,

I believe Lindy's answer regarding what happens in real world situations is

"In combat, of course, you shoot when you have to."

meaning "Damn the blown primers!" My interpretation is "Do the best you can to keep the ammo and chamber dry, forget about reloading the brass, and just shoot."

so for me it's back to the chamber apron and uber-tacticool Sham-Wow!

 

[Tribe]

Re: Altitude vs Chamber Pressure

How far up from blown primers is picking steel from face?

Any the word on the Sham-Wow-Multi-cam????

 

[azimutha]

Re: Altitude vs Chamber Pressure

Good thing most of the fighting these days is in arid climates.

 

[dontstrokeme]

Re: Altitude vs Chamber Pressure

Asked Stu and he had not had a request yet....just need to figure a way to mount it so that it is removable.

 

[ranger1183]

Re: Altitude vs Chamber Pressure

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: dontstrokeme</div><div class="ubbcode-body">Asked Stu and he had not had a request yet....just need to figure a way to mount it so that it is removable. </div></div>

velcro, and lots of it!

 

[Tribe]

Re: Altitude vs Chamber Pressure

+1... the key is the material.