I have a head scratcher I need every ones help with. A little back ground first.
I have a S&W 1500 in .243 I've had for 30 years as my truck/coyote gun. The gun has at least 2000 rounds through it but it has been kept clean and still shoots .5" groups with 72 gr Barnes Varminators. I have Lyman dies I've had for the entire life of the gun that have loaded all these rounds with.
Here is the problem.
The last year or so, every round I chamber is very tight, I almost can't close the bolt. I full length resize and try to bump the shoulder back just a touch, every time I size. cases are trimmed to the right specs as well.
For the first time in 30 years of reloading, I had excessive pressure to the point of blowing the primer and sticking the bolt with one round. None of the other cases show any sign of excess pressure. I have not tried to chamber a factory round to see if it is to tight.
Do dies ware out?

You probably are not bumping back far enough

How many firings on the brass? Do you feel a lot of resistance when seating bullets?


X-verminator

maybe pulling the shoulder back out when the expander ball comes thru the neck.

Sounds like the chamber is not allowing the neck to release the bullet. The same situation that you would run into with long or thick necks. Check the chamber out and check the neck wall thickness of your brass.
If you don't find anything with that, think back if you started a new lot of powder or brass or bullets when the problem started.

Primers...there's been some bad lots. See MuleDeer. powdr

Primers...there's been some bad lots. See MuleDeer. powdr

Could be one or many things. Start with an empty cartridge that chambers. Separate your sizing and expanding steps, and try chambering the cartridge after each step.

Blacktailer and I are thinking along the same lines here. The reason I asked the questions I did is because I was thinking thickening necks as well.

Sometimes (not always) SAAMI chambers are cut with an excessive amount of clearance at the neck-shoulder junction. Given this kind of chamber and the case's shallow 20° shoulder angle, the brass can build-up at the base of the necks. You may find that the force required to seat your bullets goes up. One solution is to turn the bottom third of the case-neck, but the brass will eventually migrate back.

Take some measurements on the bottom third of your necks and compare it to the rest of the neck.....

X-VERMINATOR

looks like the necks were a bit thick, I turned the necks and they seem to be chambering much better. Thanks for the help everyone.