At the range yesterday and my beloved Rossi 357mag rifle bound up.  WTF?????   Had 4 rds in the mag with no way at the range to get them out as I didn't have a screwdriver with me.  Luckily, it was the last couple of rounds before we were going to pack up anyway.
Got home and while cleaning my brass, I noticed that one of the 357mag cases didn't have a primer in it.  Interesting.  Then I found another.  Really interesting.  After dealing with the spent brass, I remove the mag plug, dumped out the spring, follower, and remaining ammo so the rifle was safe as it bound up after it fired.  I played with the lever a bit trying to rack it back and forth to free it and suddenly it slid open easy as pie.
Upon inspection, I noted that there were 2 bent up primer cups that fell out when I rolled the rifle over.  Looking closer, neither had their anvils so I went looking in the action for them.  I found one and thought I was good to go so after reassembling the mag cap, spring, and follower,  I loaded up some dummy rds I have and checked function but found that the rounds wouldn't move back onto the lifter as they were being held in the magazine by the cartridge stop attached to the left cartridge guide.  
I pushed on the spring loaded cartridge stop and it felt bound up a bit so I removed the front mag plug, dumped out the spring, follower, and dummy ammo so the rifle was safe again and looked closely at the stop for damage. I didn't find any damage but under my glass and light, I could see a tiny bit of shiny brass under the stop that looked to be binding it.
I removed the buttstock, loosened the left cartridge guide a bit, and sprayed the inside with brake cleaner.  Sure enough, a primer anvil made it's appearance from under the stop and I was able to flush it out of the action.  I tightened the guide, re-attached the buttstock, and reassembled the mag cap, spring, and follower.  Then I took my dummy rounds, loaded them up and cycled them through the rifle without a hitch.
Problem solved and I cleaned my action to boot.  
 
 
 
 

Undersized primers, or...?

Not a Rossi issue that's an ammo issue.  Either reloads that are too hot, or perhaps brass that has been reloaded one too many times, resulting in oversized primer pockets.

Yes. Loose primers falling out is a solid clue past or present loads are over pressure.
One primer falling out can be any number of odd things but several would cause me to set that whole batch of ammo aside until I could figure what was going on

I know the primers coming out was not a problem with the Rossi, I posted
it because I thought it a unique example of Murphy's Law as having a
primer anvil wedge itself into a spot that causes a jam isn't likely.  
BTW, rifle was being fired by a friend and we discussed how he was firing it.  Seems that he didn't squeeze the lever tightly closed but I'm not sure if that contributed.  Also, brand new Starline brass with primers fully seated.  I'm convinced the primer issue was operator error while the primers binding up the action until I loosened them up isn't something that's unexpected.  The anvil wedging under the cartridge stop is just a wild chance demonstrating that anything that can happen eventually will.



 

Not sure how you can operate error a primer to come out of a case. I love Starline brass and I love my Rossi 45. Out of curiosity, what kind of primer were you using?



 

Operator error in that it appears that he fired it out of battery slightly, causing the issue.  I failed to mention that the 3 brass cases were all cracked 1/4" up from the rim and as I said, they were brand new brass, never loaded or fired until I did and the couple thousand rds before them from the same batch were all fine so a 'randum' 3 bad cases in a row it mighty tall odds.  



I went back to the range after cleaning, removing the brass anvil, and a thorough checkout and as expected, it worked fine.