SmallCaliberCentral

If I run my sized cases through a mandrel before seating bullets will it give me more consistent neck tension.

It should.The same as the expander button in the sizing die performs.I'm guessing you do this because you don't use the button in the die,to expand the neck.I don't do that,but it will give more consistan neck tension than just using a neck bushing without any kind of expansion.It's all about consistant neck wall thickness.Better brass,sorting,and turning are a few of the alternatives in uniform neck tension.

I love the Lee collet neck sizers myself. I have tried a couple of other brands in other calibers and found the least give me less bullet runout, when I check them for concentricity 95% are olus or minus .001. I square my necks after every firing and also I do not polish my cases in a tumbler. That little bit of carbon on the inside of the neck acts as a lubricant. To help it out after adding the powder I use a small brush and brush a little talc in there (babypowder) works fine. I anneal the necks after every third firing, I have some 308's that are on their tenth loading and necks are like new. Guess I am a bit anal, but the least little thing can throw you off on a long range shot.