OzFclass

During the nationals, many people were getting blown primers and signs of over pressure when shooting in the rain. I was using my 6 Dasher in the worst of the rain and was very careful in keeping my ammo and chamber dry and didn't have any problems (and accuracy in heavy rain was great).
I recently did some testing with my 284 in the rain and couldn't keep the ammo or chamber dry. (I had a towel over the gun, but the cases and projectiles got wet from my wet fingers). All of the cases fired at this time are now junk. The bases have expanded so much that they wont go near a case holder. The cases which were fired before the rain came show no problems at all. I have a tuner hanging off the front of this barrel so I know its not water in the muzzle.
I expect cases to stretch from reduced case wall friction, but why do they also expand, indicating high pressure?

Rod,
If you are talking about case head expansion then I believe it is also due to the reduced wall friction. When wet the case grip is greatly reduced and thus most of the backwards thrust on case is through bolt head instead of partially absorbed through case wall, chamber friction. It is surprising how much absorption of bolt head thrust is undertaken by the brass walls. (and hence thinning of the case just above web). This causes increased brass flow in the case head (not due to increased pressure just increase in bolt thrust) resulting in blown primers, and ejector/extractor brass flow.

Same thing happened in Brisbane Nationals to me. I kept the gear dry in first range with plastic sheeting and a towel. By the time the second range came, towel was soaked and so were fingers. Those cases were trashed too!!

Rod, I too have experienced this and made up a rain protecting cover for my action along ICFRA guide lines. If I can find a photo I will put it up on this thread. It utilises a clear plastic sheet (ICFRA requirement) so the action and bolt are in clear view.

This is what I think happens with wet cases to cause pressure problems. Rain on the cases reduces the chamber volume by occupying some of the chamber space and as we know liquids are in compressible, (in this example) so the pressure increases proportionally with the decrease in volume.

This is just my thoughts/opinion on what may cause the increase in pressure I would like to make it clear I have not undertaken any testing to verify this but as Mythbusters would say "it seems plausible".

Ian

This also shows the importance of removing all the case lube after sizing and oil out of chamber after cleaning. I finally worked out why a couple of cases in every box of my 284 were getting trashed after every firing but others were fine. I now degrease and mop out my chamber very carefully after cleaning.

I also have a plastic cover which I used in Belmont. I used a towel which is very good at absorbing water from my fingers as well.
In the testing session, I had a towel, but it didn't seem to soak up water on my fingers at all.
I suppose these cases I was using were already known to be soft even with a dry chamber.
What seems strange to me is that once I used my 6.5 Gertrude (WSSM) in pouring rain once. The cases were soaked and the action was swimming in water, but these short fat cases, known for extra bolt thrust were fine, and accuracy was perfect??? Maybe I had them loaded light enough due to the minimal case to wall grip even when everything is dry.

<a href="http://imageshack.us/clip/my-videos/534/1uojuwucbvdryzawuacmdw.mp4/"><img src="http://img534.imageshack.us/img534/5284/1uojuwucbvdryzawuacmdw.mp4.th.jpg"/></a>

http://img534.imageshack.us/img534/5284 ... uacmdw.mp4

This is a very short video of me testing my 300WM out in my Shehane stock using my rain protector. Watch this video to see how well the cover works at the range. I attach it to the scope with two bands of velcro and it weighs next to nothing. The current rules allow you to place a waterproof coat or jacket over the action which completely blocks the view of the bolt from the range officer. This cover of mine is simple to make and much better than throwing a coat or towel over the action.

Its also well under the ICFRA size limit! ICFRA require the rain cover to be attached to the rifle so the cover cannot be blown into another shooter on the mound. This is another excellent rule that the NRAA should consider for inclusion into our SSRs.

There is room to place the ammo under the cover as well but as its not raining the ammo is placed to one side.

Ian

That's great Ian - I might modify my setup on those lines and keep ammo and chamois under sheet - also worth tipping cases upside down (projectile down) so you can keep the wet fingers off case body.

I have a pressure gauge setup here now and one thing I noticed - first shot on cleaned barrel (normally low shot and low velocity) actually had correspondingly less pressure but trashed the cases the worst. With careful attention to getting all traces of cleaning fluid out of chamber (I even wiped shells with Rosin for extra grip) you could get rid of this issue completely. I concluded that case head damage is not only related to pressure but case grip plays a major part. The fluids would replace some volume but if it was the major factor we would see an increase in pressure corresponding to case head damage. - I might run this experiment again with wet fingers on some older cases at some stage.

For my plastic sheet I went to a hardware store and got the sort of plastic they use for patio rain curtains. It is stiff enough to stay in shape, but hangs down enough over the chamber to stop wind coming in from the side.

Another cover I made was a stiff A4 divider from a newsagent. When fixed to the top of the scope, this stays flat, making it easier to get your fingers into the ejector port.
I use the big floppy one in my gun with an ejector or when it is windy. I use the one which stays flat if there is not much wind, or the gun without the ejector.

Only problem is.

When I bring them it doesn't rain and Vica Verca.

Parker Ackley addresses the issue of loss of friction on cases. If I recall correctly, he was able to demonstrate that a 30/30 Ackley case would stay chambered without backing out or stretching loaded to 40000 psi. In other words, a 30/30 case was capable of absorbing 40K psi of pressure. When the cases were lubricated, they stretched to the extent of the rifle's headspace - and he boosted that to a full 1/10 of an inch by the end of his experiment.

Incidentally, he used a clunker Winchester 94 action with the locking wedge removed for his experiments & had to manufacture an extended firing pin to pop off the shots at the end.

I watched James Corbett shot that wet day in Brisbane & took no other precautions than to keep his loads under cover & dry his hand before loading each shot. I didn't see him pop any primers & he shot a 50 with a bucketload of Vs.

Rod, this is an interesting thread and I use the heavier plastic sheet that outdoor cafe's use like you. Its needed as it hangs better and is not badly effected by wind.

Dave, I'm fascinated with your pressure testing of barrels to see what you find. As a technician who spent a few years involved with calibrating load cells I know how useful strain gauges are. Are you gluing the strain gauge to a test barrel for your testing of pressure or does your equipment use something else? Looking forward to hearing about your results when you finish your testing.

This type of equipment: http://www.shootingsoftware.com/pressure.htm

I wonder if placing drops of water on the cases at the shoulder then the head would produce different results. Very interested in your testing and its a shame I dont live closer to you as I would love to get involved.

Ian

Ian,
I have a scope cover made out of similar plastic sheeting. It didn't do me much good in Brisbane, when it was sitting at home in the back of my car in WA....

Mine is cut to slip over the front and rear of the scope. Taped, and has fishing sinkers taped around the edges to add weight and keep it from blowing around.

IanP wrote:Rod, this is an interesting thread and I use the heavier plastic sheet that outdoor cafe's use like you. Its needed as it hangs better and is not badly effected by wind.

Dave, I'm fascinated with your pressure testing of barrels to see what you find. As a technician who spent a few years involved with calibrating load cells I know how useful strain gauges are. Are you gluing the strain gauge to a test barrel for your testing of pressure or does your equipment use something else? Looking forward to hearing about your results when you finish your testing.

This type of equipment: http://www.shootingsoftware.com/pressure.htm

I wonder if placing drops of water on the cases at the shoulder then the head would produce different results. Very interested in your testing and its a shame I dont live closer to you as I would love to get involved.

Ian

Ian, yes this is the system I purchased. Along with another 6 strain gauges. I had one glued to every barrel and ran it with a PVM chrony (and later a magnetospeed) and few other technical gadgets. After Raton I am hoping to write a few of these tests up with Peter Smith when we get some time???. I am thinking of selling the whole lab now though (including quickload) as I have done most of what I wanted to do and certainly have all my barrels working well now. . Of interest - although I saw a great deal of difference from barrel to barrel I have settled on one load for all my 284's and one for all 3 RSAUM's. (although muzzle velocities and pressure curves are quite different)

Dave, I would love to have a play with pressure testing just to see if it coincides with the pressure signs we all read on our cases and primers. It certainly would be interesting to see the pressure curves that coincide with an accuracy node. I dont think I would buy the test equipment and software though just to cure my curiosity.

Linda, hahahaaa, yes you need to have the raincoat for your rifle in the kit to use! Sinkers to keep the plastic in place would definitely work and in Queensland the fishing is pretty good so you get a double use

Ian

Hi Ian,
One thing that was definitely visible through the testing was case head pressure signs can be vastly different to actual pressure as described above and on a link to a test on their website. http://shootingsoftware.com/ftp/dbramwe ... 9%2004.pdf

BUT - on the plus side I think we see case yielding and case head pressure signs at dangerous pressure regardless even with perfect grip by the cae wall (in modern actions! - please be aware of the pressure limitations in other/older actions) so these signs tend to lean on the safe side but appear earlier if the case is lubed. Look at the graph in the article and you will see very significant case head expansion at 65,000 psi in all cases (pardon the pun )

I would recommend doing something very consistent in load development with this in mind.

e.g. wipe out chamber and outside of shells with acetone. Do not load test in the rain etc etc.

If you want to see the reverse then I suggest wiping a case with a light lubricant and see how bad pressure sign can be on case heads even at low pressure loads.

the bottom line is that whatever the pressure, excess case head expansion must be the guide.
one exception to this seems to be belted cases on the first firing.
I have recorded 0.003 expansion here, and was very worried, even with light loads.
then I read that case head expansion is only a useful guide on the second firing of a belted case.
not sure of why, but it proved to be a good rule for 6.5, 7mm, 30, 338, and 375 belted cases.
keep safe,
bruce.