Boyd Allen question

B

bluechip

Guest
Boyd, (or anyone who can answer my question) I saw an old post from you (2005) where you seemed to have figured out what causes the shiny area on the case neck at the very end of a fired case. People have said it is from rubbing the action when it is extracted but I'm not buying it.
 
Just so the rest of us can get our heads round this, do you mean the case mouth or where it morphs into the shoulder?
 
John Kielly said:
Just so the rest of us can get our heads round this, do you mean the case mouth or where it morphs into the shoulder?
Click to expand...

I'm referring to the very end of the neck, the same area that is cut when trimming to length.
 
I have never

bluechip said:
I'm referring to the very end of the neck, the same area that is cut when trimming to length.
Click to expand...

noticed such an area right at the mouth of the case. Been shooting BR for >20 years. I clean my necks after each firing, never noticed anything in particular of this nature.
 
I am still drinking my first cup of coffee so this may not be stellar. I used to see this on my the cases that I shot in by tight neck .222. Back then I thought that there was some virtue in keeping my case necks trimmed close to the maximum. I would monitor their length and trim them fairly often to maintain a clearance of .005. The .222 has a relatively small shoulder angle (23 degrees) and the brass is not as thick as some, which means that when a round is fired, I believe that the case is driven forward in the chamber by some small amount, and that with such a small clearance, that it would make contact with the end of the neck part of the chamber. I trim my PPC cases to 1.490 after fire forming and keep my trimmer set there for subsequent trimmings, for chambers that have a maximum case length of 1.515, and I have not seen the bright spots on the ends of those necks, also the brass is thicker in their shoulders and the shoulder angle greater. Together they make it harder for cases to be driven forward when rounds are fired. The extreme example of this are the AI cases with an even larger shoulder angle that is so effective in keeping the case from going forward that reading primers is a less reliable method of gauging pressure. I could be all wet on this but that is my theory. Now back to the kitchen for another cup.
 
I have had this problem with my 6.5-284. No one has given me a satisfactory explanation either. The shooters I shoot with told me trimming case length would help but the marks were still there. What would cause the case to be propelled forward?
 
With a smaller shoulder angle, thin brass, and a rimless case, cases are knocked forward in the chamber by the momentum of the striker assembly and (I think) the force of the primer explosion against the bottom of the pocket. The proof of this is that with light charges like those used for cast bullets, repeated use of the same case will result in progressively increasing primer protrusion from fired cases. The shoulder to head dimension is actually progressively reduced, and the neck length increased. The reason that we do not see this evidence with higher pressure loads is that the case grabs the chamber walls in its forward position, and when the pressure becomes great enough the back of the case stretches enough for the head to contact the bolt face, which pushes the momentarily protruding fired primer back flush with the head (if the load is sufficiently hot).
 
You must log in or register to reply here.
Back
Top