What went wrong? (pictures inside)

[Joker]

I recently made this 158GR .357 Magnum loads using a single stage press. I did notice that it was a little harder then usual to press on the lever but it was still making the rounds and they seemed ok.
I made a batch of 50 but some of them I was able to press on the bullet and it just seated deaper into the case. I never seen or had this happen to me. Please elaborate.

Press used was Lee Single stage using their carbide dies labeled for 38 special but it said it will do .357 magnum. I have used these dies for .38 before but this is the first time for .357. Also I do want to clearify I did reset the seating die and its probably name the same setting as I used for .38

Sorry for the pictures being a little dark but these were all able to just seat so low

Compared to a normal one that came fine.

 

[Chili]

Are your cases the same brand? In the past when loading 38 Special, I have had R-P cases allow the bullet to slip down into the case like that.

Another issue is perhaps you opened the case mouth a little too much on few of them. It happens!

 

[Joker]

They are mixed cases.

That does make sense about the rim being too wide. How can I check that?

 

[Frost]

I would start by going through the setup on the expander die again.
You want just enough flare to allow seating bullets without having the case mouth shave lead from the bullet.

 

[Tigerstripe]

i would say the seating depth is still 38.

one other thing that will happen with lead bullets is wax buildup on the depth adjustment. those arent lead though are they.

do you have a caliper to guage max and min loaded length?

 

[buddyb]

Everyone else gave good advice with checking to be sure bullet lube is not in the seating die from previous loading lead bullets and expand the case mouth as little as possible.Also screw the seating die in until it touches the shell holder with the ram up,then turn it about a half turn in and back out on the seating screw on top of the die.That should give you a little crimp.If you need more crimp,turn the die a little deeper on the press until you get the crimp you need and then adjust the depth of the bullet until you get the COL where it needs to be.