Hi Weaselthis. Ok, you should always use lube for sizing bottle neck cases, whether it be graphite or wax based. Furthermore, if you are reforming such as necking down, lube is even more important. The only situations where lube is considered unnecessary is for resizing pistol brass using tungsten carbide dies.
The second problem you are most likely experiencing is that you are running the .300 case too far into the die, pushing back the shoulder and also increasing the body dimensions. Annealing will actually cause more bulging as the brass is more maleable. Nevertheless, by not using sizing lube, the brass will be work hardening quickly anyway, necessitating annealing.
You are really going to have to re-address your reloading practices regardless of your past 25 years experience, not just to be able to form a wild cat, but also for the sake of accuracy. There is no point having a potent cartridge that will only group 1.5 MOA because you have been rough on the brass. Slow down a bit and take so try to study what is going on, you will work it all out just fine. If you can get your head around the fact that you may have to lift your game a bit for this project, you will find any obstacles a lot easier to overcome and the results will be very rewarding.
I use a basic Hornady 7m Mag neck die for my 7mm Practical: The 7mm Practical. A Practical Magnum.
I own very expensive bench rest dies but they make no difference, the Hornady neck die is fine. The reamer for my cartridge as well as other reamer options can be obtained from Pacific tool and Gauge. Please bare in mind that they are under a heavy work load at present/ this year so gather what information you need prior to contacting them via these posts and contacts so they can process your order without fuss. Throwing a heap of questions at them is currently too much too ask of them when the work load is so high.
Yes, fireforming will remedy your cases but you probably won't be able to chamber them due to the body dimensions they have been pushed too. If you try and force them, you'll risk snapping an extractor.
Hope that all helps and I hope I haven't been offensive in answering your questions.