Why does shooting in the rain cause case problems?

DaveMc · Post by **DaveMc** » Thu Jul 18, 2013 11:19 pm

From what I have seen with the pressure gauges I am 99% confident (happy to be proven wrong mind you) that we are seeing negligible increase in chamber pressure but significant increase in case head compression. This seems verified by the fact that all shooters described no loss in accuracy or POI shift (which would be associated with significantly higher pressures). I am happy to run this exact experiment (with water rather than oil) with the pressure gauges after Raton. But keep the suggestions coming it is a very interesting discussion and I welcome anyone to do some trials of their own (with due care of course)

Thinking a bit about Barry's comments overnight does raise some questions.
1) Does polished chambers and/or crush fit indeed show case head pressure signs earlier than increased headspace and rough chambers?
2) If so then perhaps those with the latter see a bigger difference in the rain as could be loading to higher pressures to start with???? :-k

bsouthernau · Post by **bsouthernau** » Fri Jul 19, 2013 9:52 am

When you fire a wet case the water doesn't stay there but turns to steam. You're actually generating more gas. Is this something that needs to be considered - I don't know.

Barry

Barry Davies · Post by **Barry Davies** » Fri Jul 19, 2013 1:27 pm

Maybe so but that gas is on the outside of the case and cannot cause head expansion, which results from internal case pressure.

bsouthernau · Post by **bsouthernau** » Fri Jul 19, 2013 8:42 pm

Let me make it quite clear that I'm asking and not pontificating!!

But surely as the case expands against the chamber wall the extra gas has to go somewhere and the most likely place I can think of is in with the other combustion products.

Barry

BATattack · Post by **BATattack** » Fri Jul 19, 2013 9:40 pm

The only real way to tell would be to put a force gauge between the bolt face and case head.

I think the "aquaplaning" concept works best in my mind. Even one drop would fill the entire space between a loaded round and the chamber in the same way a few drops will spread out between two sheets of glass laid together. There doesn't need to be an increase in chamber pressure to increase bolt thrust. . . . Just a loss in friction along same plane that the force is acting in

once this thin layer is in between it can not be compressed or squeezed out in the micro second it takes to fire a shot. But by the time you open the bolt the heat in from firing the shot and the barrel steel would have dried the case.

Razer · Post by **Razer** » Fri Jul 19, 2013 9:45 pm

I may be a bit behind the times, but, I was taught from a very early age never to shoot with a wet chamber and/or wet cartridges as it would increase the pressure on the locking lugs. Rear lockers like the SMLE were the most dangerous, even stretching the action :shock:

.
The reason given was that water is 'incompressible' and the case would never grip the chamber walls.
My gut feeling is that the actual firing would not generate heat quick enough to turn the water to steam so, effectively, it is not only a lubricant, but, it would stop the case expanding to the chamber dimensions therefore increasing pressure, albeit it slight.
Also, if the pressure was high enough, could it not push the bolt head back just that minute amount to give the projectile extra jump which would change the fine tuning on a particular load, more so if the projectile was jammed? We are dealing in milliseconds here.
Just asking. :wink:

I see BATattack has posted while I have been typing.

Barry Davies · Post by **Barry Davies** » Sat Jul 20, 2013 9:13 am

Baz,
Assuming that a wet cartridge produces extra gas by converting the wetness to steam --which I doubt, as there would not be sufficient heat generated along the case, how could it mix with the other combustibles?
To do this it has to get past the sealed shoulder, and to do that it has to produce more pressure than is generated by the powder.
Just asking.
I dont see any increase in backthrust against the bolt face as being a safety issue, simply because the mechanical design under normal working conditions, ( and I include wet ammo in that ) is more than adequate.

Where I see the increased backthrust as being an issue is because of the reduced friction between case and chamber wall, ( and the subsequent increase in backthrust,) the increased pressure between the bolt face and case head causes the head to flatten and expand in diameter. Bit like thumping a copper penny with a hammer--peening.
This only happens in extreme conditions---
Very wet or greasy case.
A slightly wet or greasy case coupled with maximum loads.
It can also happen with a grossly overloaded case without being wet but this is not because of increased case/bolt pressure, rather, increased pressure within the case and primer pocket.
My theory FWIW.
The condition of slightly wet with maximum loads is the one that would concern me most and is the condition where, I think, most primer popping would take place.

Barry Davies · Post by **Barry Davies** » Sat Jul 20, 2013 9:26 am

Thinking further, this would be further enhanced by the use of cases that are relatively soft --one comes to mind specifically.
During manufacture cases are heat treated ( annealed ) so that the case head is the hardest portion ( for obvious reasons) with progressive hardness to the neck area, which is softest,( for obvious reasons ) A soft case in the head area is going to give trouble from day one unless you use real mild loads, and even then it is doubtful that the head will not expand ( under normal conditions)

johnk · Post by **johnk** » Sat Jul 20, 2013 9:48 am

It might help to clarify if any of those who had issues at Belmont would comment on what load/velocity/case they were running.

DaveMc · Post by **DaveMc** » Mon Jul 22, 2013 11:31 am

Hi John,
I can't help with everyones loads but certainly those running 51-51.5 gr 2209 behind a 180 in the 284 (2800-2840) saw some case head issues (according to quickload this should be around 52-54,000 psi). Whilst this is not crazy pressure it is well recognized that the tapered case and small case head of the 284 means it suffers case head issues at a much lower pressure.

I also saw plenty of 308 cases as well as my RSAUM which is a medium/heavy load (2950-3000 fps - some run them at 3100!) 60,000psi measured and similar to quickload calcs but soft brass.

RDavies · Post by **RDavies** » Mon Jul 22, 2013 9:11 pm

In a Shehane, I usually run 52-53 gns of 2209. I think with bullets jammed I am likely closer to 56000-60000 psi. I hear of BR and PPC shooters using higher pressure than this, but like Dave says, not in the weaker 6.5x284 brass.

DannyS · Post by **DannyS** » Mon Jul 22, 2013 9:49 pm

Going back a bit in this topic, does adding fishing sinkers to a plastic wet weather action cover, increase the weight of the rifle? Or are these sinkers sitting on the shooting matt, and therefore, not adding any weight to the rifle?

Danny

BATattack · Post by **BATattack** » Tue Jul 23, 2013 10:00 pm

DannyS wrote:Going back a bit in this topic, does adding fishing sinkers to a plastic wet weather action cover, increase the weight of the rifle? Or are these sinkers sitting on the shooting matt, and therefore, not adding any weight to the rifle?

Danny

good question I was going to ask for clarification on the same. I think the rule is something like "anything attached to or recoiling with the rifle is included in the weight"

IanP · Post by **IanP** » Wed Jul 24, 2013 8:51 am

BATattack wrote:
DannyS wrote:Going back a bit in this topic, does adding fishing sinkers to a plastic wet weather action cover, increase the weight of the rifle? Or are these sinkers sitting on the shooting matt, and therefore, not adding any weight to the rifle?

Danny

good question I was going to ask for clarification on the same. I think the rule is something like "anything attached to or recoiling with the rifle is included in the weight"

Adam, the wet weather option in NRAA SSR's is for a coat or ground sheet to be thrown over the action/rifle and i dont think they include the weight!!!!!

Its another grey area of the rules that requires clarification. Its better to keep water out and avoid high pressure bolt lockups (or worse) than worry too much about weight. My video shows me shooting with my plastic cover attached to the scope with velcro and it makes the weight requirement. If its necessary or not to make weight when raining I dont know but would love to hear from someone that does!

I did not find weights necessary to keep the thick plastic hanging down in the wind but Linda is probably using a different design altogether. We need her to post a photo of her rain cover to she how see has designed it.

Ian

Barry Davies · Post by **Barry Davies** » Wed Jul 24, 2013 9:22 am

A little bit mixed up there Ian -- the groundsheet and / or coat is for laying on. The preceeding rule allows for a cover ( mat ) to be placed over the fore end and action to prevent water getting in.
Mention is made several times of covers etc to prevent ingress of water to the action but it is not specified if this is to be added to the weight of the rifle.
Another rule clearly states that any "attachment " is to be deemed as part of the rifle for weighing purposes but does not exclude any attachment for preventing ingress of water.
The way I read it is that if the cover is not " attached " it does not figure in the overall weight.
Needs clarification.