THE REST OF THE STORY...
Several of you were very close in your determination of what happened and many of you posted very knowledgeable replies. I am impressed!
First of all the two bullets, shown with this new picture, were originally the same, both are .338 cal , 250 gr Nosler partitioners. (not bait bullets) This little learning lesson was provided by a dear friend of mine who has hunted the world and is a very knowledgeable reloader. He owned two almost identical Model 70's, same mounts, scope, trigger pull.......EXCEPT the bores were different. One was a 7 mm Shooting Times Western, the other is a 338 Win Mag. He decided to develop a better load for the Win Mag, using the Nosler 250 gr partition bullet. He loaded 3 rounds of the new load, went to the gun safe and knowing the similarity in the rifles, carefully chose the 338 Win Mag, to try his new loads. Fired first round… ,second round…, and on the third round, as you can see, there was no more…. He called me a few minutes after the explosion and told me what had happened but did no yet know why it happened. My first question was, "how bad are you hurt?". Thank goodness he was not seriously injured (only had one small piece of the stock imbedded in his cheek), but needless to say, he was "all shook up".
He was shooting off the bench with the rifle in a shooting stand, he was only holding the pistol grip and steadying the butt of the rifle with his left hand, otherwise it is almost certain that he would have lost his left hand and /or arm. After he calmed down a little, and of course, changed his pants , he returned to the scene. Covering about a 25 yard area, he retrieved what you see in the picture . Not until after looking at the barrel and noticing the markings did he realize what a dumb mistake he had made. Of course it was the 7mm. Our question is still…. how it managed to hold together until the 3rd shot, and we were even more amazed that he was not seriously injured..
Epilogue:
This did not come out of a book I took these pictures myself. It was an actual experience by a friend who is not a newbie to shooting, hunting and reloading, and could just as easily happened to one of us. We may not have been so lucky as to not have serious injuries.
I had 3 rifles that were almost identical too, all with black satin stocks, Leupold scopes, etc. I now have a gray one, a black one and a green one hehehe. You can never be to careful, even if you have checked........, CHECK IT AGAIN!!!!
Perhaps these very graphic pictures have impressed upon you the importance of knowing you are shooting the correct ammo in the correct rifle, and will help prevent serious injury to you or someone else.
Be safe…Have fun!
deadeye2
) but most accidents are a result of more than one failure. Could this have been caused by a combination of someone trying to chamber the wrong cartridge and having a firing pin stuck in the extended position? 
