Tight chamber?
 

I have a Browning A-bolt in .280 Rem that has about 300-350 factory rounds through it. I decided to work up a load for it even though it has always shot exceptionally well with factory Remington ammo. I measured my max length with a Hornady overall length gauge and seated my bullet about .02" from the lands. When I got to the range, I had a difficult time closing the bolt. At first I thought I didn't bump back the shoulder enough but I had one of the bullets stick in the rifling when opening the bolt. When I got back to the bench, I realized that the modified case was not seating all the way thus causing my Max COL to be incorrect. I attempted the chamber more cases without success. The sizing die was originally adjusted to about 1/4 turn beyond touching the shell holder. By increasing to about 1/2 to 5/8 additional turns I am finally able to barely chamber the cases. Could this rifle have an extremely tight chamber? Could a small base die help?
Additional info - once fired brass through this rifle; all factory ammo chambered fine

No, you seated the bullet wrong.

If the once fired brass was fired from your rifle, then your problem is probably bullet seating depth. Bullets from different manufacturers have different shapes, and different seating depths. Try seating your bullets a bit deeper first.

Yes, I did seat the bullet wrong. After forcing the modified case further into the chamber, I found that the max length was actually about .03" shorter than originally measured. I also blackened a couple of cases and chambered, all have the black removed just above the case head at the bulge.

....Once you realized the factory ammo chambered up fine plus the fact you were obviously jamming the bullet into the lands, a big red light should have come on for you. By the way... are you lubing the inside of your case necks well? If not, the expander plug can possibly actually pull the shoulder of the resized case forward upon the press stroke removing the case from the die. Guess what happens??.....

Dad has a bottle of powder graphite that he applies to the inside of the case neck with a cotton swab.

One 4 oz bottle would probably last a lifetime the way he uses it.

Okay I'll be the cat that gets killed by curiosity. WHY?