Thread: Interesting...

As I mentioned in another thread I was doing some shooting in the rain and although my ammo was dry it was hard to keep your hands dry so the ammo picked up some moisture on its way to the chamber. Once I got home the ones that had some moisture on had a nice round stamp on the head and a crescent shaped indentation on one side of this with the brass starting to shave off around the indentation
This is Lapua .308 brass necked down to 7mm08. I will back it off half a grain to give a bit of grace and keep the load a bit more useable across varying conditions. The interesting point however was I measured for case head expansion comparing the rounds fired with no pressure signs to the ones which carried moisture and produced shavings and there was no difference...
Bit of a head scratcher and some may say that this would suggest the loads were already too hot but measured some lighter loads too and they were the same.
Thoughts?

hori got any photos? The crescent sounds like an ejector mark. How much juice you got in the tank?

Im no expert by any means horihunter but I have found the same as you regarding case WEB expansion not head as this aint gonna expand unless something is really wrong? I thought the place to measure was about the place you would expect case head separation to happen.
In my rifle no difference in the above measurement from book min to well over book max and shaving brass of the head.
Primers seem to be unreliable pressure indicator also, fed crater at min load cci arnt even very flat when the brass has said "enough"
So now I just look at the brass. Go up till it extrudes into the bolt recesses and is shaved off on opening. Then back it of from there for the sake of brass life.

I am a novice! but this is what I have found so far I am sure I will be corrected if need be

There was an article in NZ huntin' n' wildlife or some other local rag a fair while back by Chaz Forsyth. It talked about a few things but mentioned excessive pressure caused by wet ammo. I think from memory (don't quote me) it had something to do with the seal of the bullet in the lands. All I can remember was his take home message keep it dry.

Originally Posted by yerimaginaryM8

There was an article in NZ huntin' n' wildlife or some other local rag a fair while back by Chaz Forsyth. It talked about a few things but mentioned excessive pressure caused by wet ammo. I think from memory (don't quote me) it had something to do with the seal of the bullet in the lands. All I can remember was his take home message keep it dry.

The pressure rises because the moisture replaces the air in the chamber around the bullet & doesn't compress effectivly making the chamber smaller & it is also possible that the water lubricates the case a little so it doesn't grip the chamber as tightly as normal causing more thrust on the bolt face.

If you are running close to max this will have more of an effect....

I found out years ago the hard way with a loose chambered 243, hot loads, lots of rain & bombing goats.

I discovered that it is hard to keep loading bullets into the chamber when there are primers in the action.......the goats didn't like it either, nor did the brass.

The worst thing was I asked every one I knew including all the local "experts" in the gun shops & no one could tell me what happened, I had to figure it out myself....these days the internet is good for some things

Case head expansion is exactly that and it is measured at the largest part of the taper prior to the extractor recess. Its evidence varies depending on the quality of brass and loads and is more prolific in my experience in long action cases. I get some in necked down lapua 30-06 brass with a medium load and then it settles after the first firing. If you get it in short action cases (.0003-.0005) there is something wrong alright, unless it also settles.
Half cresent marks are the ejector rubbing on the head of stretched brass as the bolt is actioned through primary extraction. ( Rems and Tikkas have pretty good ejector springs and sharp ejector pins as well. So it doesnt take much to get the marks) It is interesting that damp hands can cause such a difference.

I knewsomeone would ask for pics.... Will try to get some from my phone tomorrow, it made a full circle stamp with half cresent shaved out of one side so sounds like your on the money R93, its a tikka....
was quite surprised when I saw it myself. What Greg mentioned about the case being thrust into the bolt face harder sounds like the explanation given the case dimensions didnt vary between those fired dry and those with moisture on them. Now to make my next thread with a trajectory issue....

Originally Posted by R93

Case head expansion is exactly that and it is measured at the largest part of the taper prior to the extractor recess.

Thought that was called the web,junction from head to body. I stand corrected

Originally Posted by horihunter

I knewsomeone would ask for pics.... Will try to get some from my phone tomorrow, it made a full circle stamp with half cresent shaved out of one side so sounds like your on the money R93, its a tikka....
was quite surprised when I saw it myself.

What Greg mentioned about the case being thrust into the bolt face harder sounds like the explanation given the case dimensions didnt vary between those fired dry and those with moisture on them.

Now to make my next thread with a trajectory issue....

Very unusual not to have a dimention change somewhere without a headspace problem. Just good brass eh.

have had same phenominom hori.... Thanks for enlighting me as to why as it never really crossed my mind ive always shook it off with the oh well lol

now if you could all swithch your attention to the shooting section and solve my next question that would be much appreciated lol

Originally Posted by veitnamcam

Thought that was called the web,junction from head to body. I stand corrected

You are most likely right VC. Like everything, there are terminology differences, especially in firearms.
Rimless, rimmed, belted and rebated cases all have funny terms concerning the complete makeup, at least the way I have been taught anyway.
Doesnt mean my part names are correct either.

No grip for the brass to load up on the side walls of chamber - thus load is thrusting back more than being spread between the face and walls
Same thing happens with lube on case, oily chamber etc.

Case head expansion is really hit and miss due to factory chamber dimensions and die brands etc