View Single Post
Old January 12, 2019, 05:58 PM   #44
Unclenick
Staff
 
Join Date: March 4, 2005
Location: Ohio
Posts: 15,765
Quote:
Originally Posted by Metal god
Quote:
Going over the previous material on using a cartridge case headspace gage to determine sizing die positioning to get the correct amount of case shoulder setback,
Thanks to Unclenick and Mr Guffey all now know when so called experts use words and terms like this when it comes to reloading. They clearly don't know what they are talking about.
There's nothing wrong with "cartridge case headspace gauge". It's a gauge made with headspace to accommodate a cartridge to check it for chamber fit. You just have to avoid confusing cartridge headspace with "case headspace". This article at Accurate Shooter defines the former. But if you were thinking the two terms are synonymous, as I infer from the above sarcasm, then you have inadvertently provided an example of the very confusion I would like to find a way to avoid.


Quote:
Originally Posted by StripesDude
Semantics arguments are best had by people with nothing better to do.
That's only true if "everyone knows what you mean". This confusion about the meaning of Cartridge Headspace illustrates that is not always safe to assume. The objective of definitions is to keep everyone on the same page for accurate communication of ideas, not semantics for their own sake. That would be for a linguistics forum.


David,

That's curious about your cam-over presses. Mr. Guffey says his Rockchuckers don't cam-over, but you and Glen Zediker say yours do. I don't own green machine, so I don't know from personal experience, but I do know my Dillons do not cam-over and my Co-ax and Lee Classic Cast and Lee Challenger and my Lee Handtools don't either. The only press I have that does cam-over is my ancient Lyman Spar-T press.

Tangolima has it right. "Cam-over" is just short for 'camming up-and-over the limit of the stroke'. On all those presses of mine except the Lyman, the handle stops against a tab or part of the frame or linkage before it can reach or pass what would be the top of the stroke were the stop not there. You can tell by watching the press ram. As you depress the handle, the ram goes up and is still going up when the handle meets the stop. With the Lyman press, the handle is still moving when the ram reaches the top of its stroke and then descends a fraction of an inch before the handle meets its stop. That's camming-over. It is why Zediker's test in his next-to-last paragraph proves it.

Glen Zediker initially described cam-over correctly in his third paragraph, assuming his Rockchucker is somehow different from Mr. Guffey's several copies. However, he did a disservice by going on to provide a second definition which is really just applying an undefined excess of force to the mouth of the die with the press. That doesn't require cam-over; just enough force on the handle.

When you apply force with the press ram against a die, the press stretches. That's perfectly OK as long as the stretch is within what is called the true elastic limit of the press frame material. Within that limit, by definition, the frame always returns 100% to its original shape when the press ram is withdrawn. Once you exceed the true elastic limit, you incur some degree of permanent plastic deformation of the press. It can be a tiny bit so small it never adds up to anything important over your lifetime, or it can be so gross an overload it not only passes the defined yield point of the material (where 0.2% permanent deformation occurs), it goes on to pass the ultimate yield point, which is where the frame breaks.

On another forum, there was a fellow who broke two RCBS Rock Chuckers. His cases weren't getting as small as he wanted, so he just kept turning the die in further and further and putting more and more of his self-described linebacker-size heft and strength into it until the frame broke. He had pictures. RCBS replaced them both times.

It is apparent that what Zediker is hoping to prevent is press overloading; people permanently deforming or breaking their presses with excessive ram force. It certainly doesn't require cam-over to make that happen. Cam-over just makes it a lot easier to do because of the point of infinite mechanical advantage the linkage passes through at top dead center. But as long as you stay within the true elastic limit of the press frame, be it cast iron or aluminum, no damage will result.

The general instructions for setting up a die with the extra eighth of a turn or so (twice that for an aluminum press due to its lower elastic modulus) are expected to stay within the press's true elastic limit. The reason for it is shown clearly by Metal god's photos. It's that crack of light that appears due to the resizing force already stretching the press frame beyond the length it had when you screwed the die into contact with the shell holder. Zediker is wrong if he thinks all press stretching can be avoided by eliminating interference contact between the shell holder and die. The Lee help video for setting up sizing on one of their single-stage presses describes this at the end, as well.

Zediker gives the example of a die that made a new case -0.008" shorter. Not all dies will do that. I'm not sure I own any that do. He seems to be working on the assumption your chamber is longer than SAAMI minimum and you will, therefore, always resize enough to chamber in your own gun before the shell holder goes all the way into the die mouth, and that is patently not guaranteed. Indeed, failure to do so is the problem the fellow who broke two of the presses was having. He needed the feeler gauge Metal god illustrated (an idea Mr. Guffey first brought to the attention of the forum, AFAIK), but the press breaker didn't know about that.

The other problem with Zediker's thinking was already described. It is when you have cases of mixed hardness that don't all resize the same amount in the same die with the same amount of ram pressure. Once you have the die adjusted so no crack of light appears with any of your cases, you have ensured the resistance of the brass in the die cannot overcome the press position (make a crack of light) and you don't need to turn the dies in any further. That will get as much resizing consistency as your press is capable of in a single stroke resizing operation. It is the reason Redding came up with their Competition Shell Holders.
__________________
Gunsite Orange Hat Family Member
CMP Certified GSM Master Instructor
NRA Certified Rifle Instructor
NRA Benefactor Member and Golden Eagle
Unclenick is offline  
 
Page generated in 0.04794 seconds with 8 queries