Well at least some progress made.
With the price or unavailability of components today factory ammo is actually more cost effective than it used to be, and of course you will then have fired brass from your own chamber to reload and use again. You are able to achieve two things with a box of factory ammo; check the fit of factory cartridges in your chamber and check the fit of fired brass, before and after resizing, from your chamber, not brass from another rifle as you have struggled with.
Even the brass sized by dpcd hasn't entirely solved the problem as you say two of the cases still offer some resistance.

Please bite the bullet and get some factory ammo

Ok, send me the die and I will remove .010 from the end of it. With carbide tooling it is child's play. Then you can adjust it however you want. You obviously have a sub minimum chamber length. Or send me the rifle and I can lengthen the chamber. I use rusty drill bits for that.

Sorry Tom just saw your response.

Still trying to figure out whether my chamber is too short or too narrow.

I brought the gun to a local gunsmith who inserted a go gauge - it went in. But of course that doesn't tell me if the chamber is too narrow. When I try to chamber Lee resized cases they really jam in the chamber (I need to hit the bolt handle with a piece of wood to get them out). Not what I would expect if the chamber is too short.

But I think I will take Tom's offer and send him the die - that will tell me for sure whether it's a length issue.

Coat a case with layout die, or a black magic marker,and it will show if it is too small in OD.