Originally Posted by CZ550
One point I think Steve was making, which appears to be true in my 40 years of handloading, is that the pros in competitive matches, using the same rifle and components, have found that reducing a load does show up not only in less velocity but less primer flattening. I generally agree with that IN THE SAME RIFLE, USING THE SAME COMPONENTS.

Bob
www.bigbores.ca


I am far from being any pro, or an engineer for matter. But my observations support this statement.

For several years, based on what I learned reading commonly available literature like my loading manuals, and before the advent of internet message boards, I did a lot of experimenting with several rifles. Most notably a pushfeed Win 670 in 30-06, and also a rebarreled Venezuelan mauser in 30-06 AI, and eventually a Win 70 classic in 264.

My efforts involved brass fire formed in the rifle, resized in FL dies in a manner which only 75% of the neck was sized, and primed with CCI 250 primers.

Then I painstakingly charted charge weight vs velocity graphs for several powders and several bullets over the course of about five years. (note: my experiments exceeded the life expectancy of the 264, and it had to be rebarreled) Some loads were pushed to the point of expanded primer pockets where they would no longer hold a primer after three or four loadings. And I experienced a couple of "pressure excursions" which expanded the case head to the point it would not fit into the RCBS shell holder on my press. "Pressure excursions" being with 140 gr partitions in the 264 loaded over early production RL25. A load which shot under 3100 fps in Nov, scared the hell out of me in July.

Anyway enough background, to observations.

Loss of primer radius definitely correlates to increasing velocity, increasing powder charge, and obviously increasing pressure. The phenomenon is observable and repeatable. I feel it can be used by a very careful observer to indicate increasing pressure values. But every other facet of the load must be held identical.

But the question is, what actual pressure value does the flattened primer represent?
Hell, I have no idea! That is what the chronograph is for.

And how do you define or measure the degree of primer radius loss?

So yes, it is a tool which can be used by the very careful, dedicated, and experienced handloader. But not one to be recommended to the novice as a be all do all safety check.

Now as far as CHE. As Denton told us a decade ago, there is too much noise in the system to get any reliable information. I meticulously measured hundreds of cases before and after firing. The head expansion numbers were so random that they were meaningless.




People who choose to brew up their own storms bitch loudest about the rain.