Originally Posted by
bcp477
I did not use published data - such data has no bearing on this particular issue. I have data, in my reloading books, as to the volume of Varget per grain.....I simply calculated the minimum safe charge weight by taking 65% of a full case, by VOLUME. This calculation has nothing to do with charge tables. Obviously, one would never load a 100% charge of such a powder.....that would be WAY WAY over pressure. The danger of double ignition with rifle powders is due to excessive empty case VOLUME. The 65 % rule (some people use 70 %) is designed to ensure that one does not load such a small charge that this could occur. But, it has nothing to do with loading table data.
The minimum safe charge weight with Varget, for the 7.92 x 57 case, using the 65 % volume rule, is just under 33 grains (I rounded up to 33 grains in my previous post). So, just to be safe, I suggested 35 - 36 grains. This definitely WOULD be safe. I have done similar loads in the 7.92 x 57 for many years. With filler, as I alluded to in my previous post, you could go below 33 grains, with perfect safety - but ONLY with filler added. You will not find loads of 35 - 36 grains of Varget, let alone 33, on ANY loading table....because such tables are developed almost always using jacketed bullets....and with accuracy in the test rifle being the major consideration, as well as safety. This is a special circumstance.
As I stated before, my best PP load, for my M48, is 32.5 grains of the powder I use (Benchmark), which is only a little above the minimum safe charge weight. Nevertheless, I add filler just as a precaution....and because I have found an accuracy improvement with it, in this load. The filler bumps the pressure of the load a small amount, tricking the load to higher velocity than it would produce otherwise, but yet without the other effects of a commensurately larger powder charge. There is some evidence that the fibre filler also gives a bit of a "gas check" effect....and protects the bullet.
Anyway, fear not. The info I gave you IS SAFE. I would NEVER publish any such info unless I was ABSOLUTELY certain of it. As I have years of experience in working with the 7.92 x 57 cartridge and old rifles that shoot it - almost exclusively - I have REAMS of data to rely on.