Testing some loads with a new Accurate 300gr cast bullet mold, in my Marlin Cowboy 38-55. A mild load using 14grs of a powder to achieve 1345 fps. I have fired many of these , no problem. Using cases from a batch of Win brass I've had for years . Some cases from this lot have been shot 20 times. Other than annealing the case mouth every 10 shots , perfect. Today a case from this same lot , on the third firing ( I still have new unfired brass from this lot ) separated. It appears the front portion of the case & the bullet went down the bore & out. After carefully checking the chamber & the bore I went on to fire a few more of the same bullet/ powder combo without incident & great accuracy. I have to assume a bad case. I bought this rifle new in 1999 or 2000. Acquired this lot of brass back then. Never a problem till now. Picture is of the rear of the separated case , normal case & the bullet I'm shooting. Attachment 289893Attachment 289894