I am trying to seat 300 grain Hornady solids abd they stick in the seater stem and won't stay in the case when I seat them.
Several otrher bullets seat just fine.
Any ideas on how to solve?

I've had similar things happen in just about every caliber I own...most of the time it was because the seater stem was backed out too far and the bullet went up into the alignment chamber too far and just stuck there.

It feels like the bullet is being seated in the case and it might be, but it might also be the bullet just getting stuck too far up the spout.

Try running in the seating stem down farther...obvious but it still catches me on occasion when I'm messing about with different length bullets and back the stem out too far.

If that isn't the case then the bullet alignment portion of the seater above the neck expansion area is slightly too small and is grabbing the bullet tight enough to hold it against the neck grip tension and you might need to send the die back to get polished out.
Try another seater if you can.

Lcuk

Take the seater out of the die and put a bullet into it and see what it looks like. The seater is probably contacting the bullet right where the 2 meet and may even be leaving a ring around the ogive. If that is the case take the seater and gently chuck the stem (you may even want to wrap it with a little bit of tape) into a drill press or even a drill clamped in a vise. Now take a fine abrasive like Cratex or a polishing stone or even 240 grit sand paper wrapped around the eraser end of a pencil and gently polish the seater where it contacts the bullet. Be careful, you are only polishing. That should be the cure.

Thanks guys
I had to go pick up some reloading stuff at the GunStop in Minnetonka, Mn they suggested a different seating stem.
I tried a different one and it worked fine.

Just wondering if that was a set of RCBS dies that you had the problem with?

I had the same problem quite a few years ago, 15-20, and I resolved it by buying a set of Hornady dies. I never bothered trying another seater stem in my RCBS set. I think I even still have that set somewhere, been using the Hornady ever since.

Slowpolk Jim, yes it is a RCBS die set.