Jn316/ I have a .300 Macdonald,which is an improved 300 Win. It also takes two firings to get the case properly formed, with neck turning after the first firing. This method of measuring case head expansion, has worked well for me, as well as the man who designed the cartridge. He has built quite a few rifles in this caliber, as well as three other calibers on this improved cartridge.<BR>Most times the people having their rifles rechambered, or rebarreled, will get him to<BR>form the brass as well. He has fired countless thousands of rounds, using this method with no mishaps.<BR>After all of the discussion of this method being unsafe in the last few days, I referred to my loading log. <BR>In the log including the .458 & .375 magnums,<BR>on down, the loads I have chosen safe for my<BR>rifles, are usually two to five grains powder<BR>less than the load book maximums. One example<BR>is for two .375 H&H rifles, a Mauser and a Sako, the load I chose to be a safe maximum,<BR>using the matching components, same lenght barrel, 270 gn X bullet, is the starting load<BR>in the Barnes manual. With two more grains powder, there were no visible signs of pressure, but only an increase of 30 fps and<BR>more noticeable recoil.The measured expansion<BR>was .00035",(one third of one thou.)so I reduced the powder to start loads. Accuracy was good at this point as well. My point being to all this, is if all my rifles have loadings below book maximum, and I do use the coinsiding manual,to match bullet make,<BR>there is measurable expansion, than I would<BR>have to think this method is safe.<BR>If you use Centurions info, new cases, and these measuring proceedures, you should come up with a load, that you have some confidence in. Hope this helps and good luck. <BR>PS. If the first firing does't completely form the case, there is a good chance there is no measurable head expansion. If you confirm this ,than I would say you have a <BR>Mulligan.
