I have one of the first 300 RUM model 700 rifles that was available in this area when they introduced the round in 1999-2000. I got the gun fro the original purchaser and he never fired the rifle. That is the history of the rifle. My problem is that when I got it I purchased several hundred once fired cases. and a set set of Hornady Custom Grade Dies. After full length resizing the brass still would not chamber. I cursed the dies and slowly ground the shellholder so that the shell would go further into the die and be sized more. I finally found where I could get the brass resized to where it would chamber with minimal bolt pressure and reloaded some rounds to try it out. The fired brass chambers easier that the sized brass due to to fire forming in the chamber. Now my problem started once again. When I reside the brass trying to adjust the dies for minimal case resizing but resize the neck my brass was difficult to rechamber again. I am talking some serious pushing on the bolt. I finally broke down and bought a box of Remington Premier Ammo and guess what I can barely get the bolt closed on factory ammo. I was going to but a RCBS FL sizing die but after trying factory ammo I am not sure that this will cure the problem. What do you think about smoking-sooting an empty case and trying to find where the tight spot is and then trying to polish the chamber in that area ( spin a once fire case case with some super fine abrasive ) to fix the problem? Or do I need to find , borrow or rent a 300 RUM finish reamer and relieve the chamber a little. It doesn't seem like it will take much material removal to end up with a chamber that will close on a case like it should . Has anyone polished up a tight chamber like this with positive results?