Maybe 30 years ago I purchased an Argentine Mauser Model 91 long barreled rifle in military fit, and proceeded to convert various 30-06 brass. Initially I fired a bunch of them with the Hornady 150 and 174 grain 0.312" bullets and used them for deer hunting successfully. Later I converted to shooting reduced loads using lead projectiles and never had any trouble with my converted brass. Recently I found a bag of about 100 of them with the 174 grain J-Bullets and decided to shoot them. I got good accuracy with them but more then half of them resulted in cracks running down from the bullet opening over the entire neck and down past the bevel onto the body by about 1/8". And sometimes there were more than one crack like this on each case. So, what is the problem here and what can I do about it? Or do I need to just throw these away and start over with new brass in this caliber which is available for sale now?