For decades, I defended the notion of miking cases to get an idea of the internal pressures being developed. I'm the editor who originally published both Bob Hagel's and Ken Waters' articles on how they do it. I also published Waters' "Pet Loads" article as a supplement for his Pet Loads book.<P>At the time, Waters and I both considered Hagel's method extremely risky. I still do (because it IS!). I supported Waters' more moderate approach. I've since learned how foolish and unreliable any variation of this basic technique is.<P>� Many cases don't expand enough, even at 80,000 lb/sq in., to warn of risky or excessive pressures.<P>� Catastrophic failures of overloaded rifles may occur with either the first over-hot round, or they may occur only after years of repeated use of over-hot loads. In the latter type of failure, the rifle has appeared "safe" with these loads, clear up until the time one round "caused" the failure "for no apparent reason."<P>� 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. Cases already too hard to show "excessive" expansion here (some, even at 80,000 lb/sq in.) are especially likely to become brittle in repeated firings and reloadings, and spew wild gas and bits of brass into a shooter's face. I have on hand now a rifle utterly demolished when half the head of the case blew back through the action. The rest of the case is still in the apparently unharmed barrel, but the receiver is in many pieces, and my friend still has one piece of brass in his face (a larger chunk was surgically removed).<P>� The maximum safe limit for many rifles and cartridges is well below the level of peak pressures that many cases can handle without any discernible or measurable indication of excess.<P>� The less experienced you are in the use of this method, the greater is the certainty that miking your cases will inevitably lead you to accept dangerously high pressures as "safe."<P>Careful lab tests of many typical "pet" loads, developed by attention to traditionally accepted "signs" of pressure, have shown their peak pressures to be 70,000 to 75,000 lb/sq in. The highest SAAMI "safe" pressure I know of, for any cartridge or rifle, is 65,000 lb/sq in. Most are lower. Many are much lower.<P>Some carefully lab-tested loads, developed by miking case rims, webs, and expansion rings, have developed 80,000 lb/sq in. without measurable expansion.<P>Stay well below the maximum charges listed in the manuals, and you'll be worlds safer without significant sacrifice in down-range performance. No micrometer is a reliable pressure gauge.
