measuring case head expansion?

[bigbores]

Is this a help tool when developing loads or can I get the same info by watching primers, primer pockets, sticky and shiny cases?

[cherokeetracker]

Yes it is If you are getting high pressure, yet your primer does not show it, You can tell that you are getting into the higher pressure by measuring the case right close to the Rim. Some primers do not flatten even when you are getting higher pressure. Just be sure and measure a before case and then you know that if you get a case that's 1-2 thousands larger,, Diameter, then you are starting to get into high pressures. At that measurement quite a bit actually.

[Kurt]

A blade micrometer is what you need. And it needs to read in ten thousandth increments. It is also best to use some factory ammo to get an indication of the expansion to expect in that brass when it is reloaded.

[mart]

Depending on the revolver, sticky extraction and/or shiny spots on the case heads may be putting you well into the danger zone. Flattened primers is not a good indicator at all. Some primers will appear flat with normal loads some never show flat with hot loads.

Around twenty year years ago I conducted a test of every heavy cast bullet I could find for the 41 magnum. Back then there wasn't much for data nor were there the good ballistics programs available today nor did I have the computer savvy to run the programs that did exist. I used a micrometer to measure case head expansion of all loads I tested. I used Winchester factory ammo for my baseline and Winchester brass to work up my loads. I would recommend the same procedure. Select a brand of factory ammo for which you can find brass and take your expansion readings from that. And not just 5 rounds. I shot a couple boxes of factory ammo through two revolvers to get my expansion figures for each gun. When my loads match the factory expansion figures I call that good. Once that figure is established I'll go down in half grain increments till I find the most accurate load for that powder/bullet combination.

A good one inch standard or blade micrometer will work. Preferably one that reads in ten thousandths. I take the reading just forward of the rim and take readings all the way around the case till I'm satisfied I have taken the largest reading for the case. It's a fairly time intensive procedure and requires new brass for any reliable results. Today there are myriad sources of reliable data and very little need to conduct case head expansion tests on handgun loads, other than for one's own interest.

[bradshaw]

bigbores.... a basic rule when miking a case through the web is, 1) mike a new case before loading; 2) mike after firing; use a micrometer, as a dial or digital caliper is much too crude. Important to start with unfired brass.

Primer reading often says as much about the gun's mechanical features, headspace, firing pin, firing pin hole, hammer fall, etc., as about pressure. Dimestional sloppiness may yield false pressure signs. With revolvers, you may glide into ROCKS & DYNAMITE before the primer says so.
David Bradshaw