HI,
All the guys have already said the right thing about measuring from the ogive. If you want to load consistant rounds then one of the first things to get is a Sinclair comparator.
I'm still interested in your comment about some seating harder than others. Given you are using one of the better seating dies that delivers an aligned pill to the neck I feel you may have inconsistant neck tension. Thats bad for accuracy and the hard neck brass inferes early failure due to cracking.
I suppose there are a couple of things to say before I go any further. Excess neck tension, eccentric projectiles, neck turning, neck sizing: all this is focussed on squeezing out a bit more accuracy, but if you have a shop bought bolt rifle and you are taking shots under 200 yards at a 4" plate then even without all this hocus-pocus you'll still hit the plate if you do your part. So if you are predator hunting then you have 'em nailed with what you have already got.
Having said that, I only have shop bought rifles and as a hobby I choose to make the best ammo I can make with the resources I have. On that basis, some time ago I also found that some rounds were seating hard and that there was inconsistant seating depth. I bought a Sinclair comparator to measuire from the ogive so I knew where I was starting from and a hand held propane torch to anneal the necks. I did a fair bit of reading and found that if I heated the necks in a Lee case holder in a battery drill until the necks got a slight blue hue and dunk 'em in water then that was all the heat that was needed. Those two devices solved my inconsistant neck tension issue.
Some time later another guy got it into my head that if the projectile is not dead in line and straight along the axis of the round then that can cause inaccuracy too. I bought an RCBS case measuring tool to measure this new found scourge to accuracy, a Redding Competition seating die ('cause I coudln't get a Foster)to ensure straight insertion of the pill and a neck turner to ensure the neck dimension didn't offset the pill due to irregularity in neck wall thickness. Note* I was told by those that know way more than me that if you use a neck turner (K&M is a good one) you should use the K&M expander before neck turning.
I have rotated the case half way through seating a pill and I note that Barnes recommend that proceedure, but with a good seating die there is at least less need for that to be done because they drive the pill straight to start with.
I would say though that all this is a bit of a waste if you FL resize. That amount of case expansion that goes on just overrides all the work that you put in. I would also say that I have had trouble with a neck sized case not chambering quickly and missing a shot.
My next step is to use bushing dies. It never ends, but my wife knows what I want every birthday and christmas.
It all comes down to working out if you want to make the best ammo on the block or do you want to hit a 4" plate at 200 yards. You don't make it any deader by hitting a 1" coin at 200 yards, but cricky it makes you feel good.