I see Mr Guffy decided to show up.
OP, do whatever makes you happy.
But I suggest ignoring distraction for now. Focus.
1) Your resized brass chambered easily.Thats important. Your problem is not in the sizing die or operation. Your rifle chamber,as a gauge,proved that.
Putting powder in the case did not change anything,unless maybe you have powder in the case neck. Over compressing powder can be an issue.
2)Remember,the brass fit till now. SEATING The seater die body is a slip fit on the cartridge case. Brass should fall in,and fall out..It just holds and supports the brass for seating.It does not reform the brass.
Seating should not change the brass that easily chambered.
Except for one thing. The seating die will crimp the neck into the bullet.
And new reloaders don't think of that. So,instead of reading and following the die instructions,they intuitively screw the die body into the press till it contacts the shellholder.Bingo. Crushed case. But the eyes don't see it.
Next,they write a post in TFL "My .223/5.56 ammo won't chamber...."
Then people go back to talking about sizing and gauges and headspace. Mr Guffy shows up and tals about old milsurprifles with excessive headspace,he's the only reloader,and he has a quick draw feeler gauge.
All in the world I asked for is a measurement over the shoulder before and after you seated bullets. You can substitute a factory load or any flipping piece of 223 brass that will easily chamber.
I don't see why its so hard.
I believe the bullet scuffing was a red herring.IMO,collapsing the shoulder made the ammo eccentric. The bullet is off center.
I also believe something else.
3) My theory could be WRONG!! I'm OK with that. I'm happy to eliminate it as a possibility. Truth,not ego. That's why I asked for a measurement FIRST,