lilquiz
Member
There is a method used to check over-pressure by measuring the base of the cartridge with a micrometer.Does anyone use this method and what are the tolerances.
• Cases work-harden in use. Repeated use makes them become brittle in the crucial portion exposed in the breech — typically 0.200 inch of the head of the case.
Anyone who wants to test my conclusion can do so for themselves, with no special equipment other than basic reloading equipment and a micrometer. Here is the test:
1. Prepare about six matched pairs of cartridges, with powder charges in about .5 to .75 grain increments, within the safe region allowed by a competent reloading manual.
2. Prepare a piece of graph paper with grains of charge on the horizontal axis and your choice of PRE or CHE on the vertical axis.
3. Warm your rifle by firing about three shots through it. Try to make all the subsequent shots at the same chamber temperature.
4. Fire the 12 cartridges in random order.
5. Place a point on the graph for each of the cartridges, showing your choice of PRE or CHE plus the powder charge for all 12 cartridges.
If you get pairs of points closely grouping around an obvious trend line, PRE/CHE works very well and I'm a monkey's uncle. In the case that your pairs of cartridges are perfectly identical and your choice of measurement system has no error, each pair of dots will occur at the same place, i.e., one on top of another. If you get widely scattered points, with some low charges producing high PRE/CHE and some high charges producing low PRE/CHE, then you have the same result as I got. In that case, you have to ask, what is the smallest change in powder charge that PRE/CHE can reliably detect? The answer to that will permanently disabuse you of using either system.
Then Olin info on Cartridge brass here. > http://www.olinbrass.com/companies/fineweld/Literature/Documents/Alloy%20C260%20Data%20Sheet.pdfmodulus of elasticity- Cartridge Brass-
Material is 70 copper/30 zinc with trace amounts of lead & iron , called C26000. Material starts to yield at 15,000 PSI when soft (annealed), and 63,000 PSI when hard.
Material yields, but continues to get stronger up to 47,000 PSI when soft, and 76,000 PSI
when work hardened. Modulus of Elasticity is 16,000,000 PSI. This means to pull a 1.000 inch long strip to 1.001 inch long induces a 16,000 PSI stress.
So if you pull a 1.000 inch strip to 1.005 inch long, you get about 76,000 PSI, which is the max obtainable.