Hoping someone can help diagnose a problem I'm having with a shilen barrel.

While my CBI 260rem barrel is at the gunsmith having some work done, I swapped my backup barrel on - a prefit Shilen 260rem bull barrel from NSS.

I started working on handloads, used the hornady tool to measure the lands for some hornady amax 140gr. And set my seater for .020 off.

All was well with the rounds until I tried chambering them. Bolt required a lot of force to close, and also a lot of force to extract the round. This was with the ejector pin removed from the bolt btw.

Upon inspection, the projectiles have a scuff mark on one side. Unchambered rounds off the reloading press are pristine.

Measured runout, under .001". Just to make sure, I used the hornady concentricity tool to get some rounds dead on 0.000". And tried chambering them. Same deal - scuff on one side.

So I tried chambering some ABM 260rem match ammo, it chambered perfectly, little force required on the bolt, and zero marks on the projectile. I measured the projectile diameter - 0.2635". Measured my amaxes and they were 0.264".

I took a bore brush and cleaned the ever living crap out of the chamber. Then tried chambering a round, same problem.

So I am pretty sure the problem is not:

* dies scuffing the projectile
* runout
* jamming into the rifling
* ejector forcing rounds to scrape the chamber
* dirty chamber

Anyone seen this problem before? What else could the problem be?