Once the neck is squeezed in and NOT expanded, and the brass is trimmed back a little so neck issues are excluded,
Then it's usually feeler gauges under the brass to see if it's a side wall/shoulder issue...
When loading for a specific rifle, I have ZERO reservations about buying common dies and modifying the dies to fit the rifle. In fact, I encourage it.
$40 or $60 worth of common dies to get brass/rounds that specifically for your favorite shooter is cheap compared to several hundred dollars worth of 'Competition' dies to make rounds for that one specific rifle...
For rifles I own that have specific requirements, the dies set right behind the rifle in the safe.
I know if I have that rifle out, I'm going to reload the brass, so when the rifle goes back in the rack the dies come out, and that also keeps them from getting mixed in with other dies, case holders, etc.
The ammo for that specific rifle usually sits on the die box behind the rifle also.
.30-06 die is not by any means a perfect 'Bulge Buster', but it will push the bulge back in slightly further down without screwing up the shoulder.
The case holders seem to get thicker above the floor plate all the time...
This is a DEAD STOP for the die, no amount of screwing the die down, or 'Over Camming' the press will overcome a dead stop, you are only overstressing the press for no good reason...
The stupid/easy way to tell if it's a shoulder/case bloat issue is to stick feeler gauges between the brass & case holder.
This will bump the shoulder back AND push the case in a little more.
This narrows it to two issues you need to look at instead of 5.
I don't sell it as a 'Fix All', but it does narrow things down...
Sizing the body, especially lower body on .308 brass with a .30-06 die is an old loaders trick.
Most cases have a 'Parent' case they started from, parent usually being older & longer than the current version.
We .308 shooters just lucked out with a super common .30-06 dies, which are cheap and make for an excellent lower case sizer without screwing up the shoulder.
.308 & .30-06 have a taper to the case, so taking a little off the bottom of the .30-06 'Bulge Buster' die will allow you to undersize the brass if you have a REALLY tight chamber without screwing up the shoulder.
-- I ALWAYS use feeler gauges under the case if the factory .30-06 die doesn't do it out of the box.
This tells you if it's case holder or die reach/mouth profile.
-- I *Usually* shave the top of the shell holder when a .30-06 die doesn't do the job out of the box.
No sense in modifying the .30-06 die until you KNOW where the problem is...
A case roller (like a Case Pro 100) is as close to a perfect solution as is commonly available for lower cases, extraction rims & grooves, etc., But not everyone wants to shell out $1,200+ for a case roller!
Just hearing $1,200+ makes most home loaders shudder and I don't blame them!
It takes a LONG TIME at 200 or 300 rounds a year to see a reasonable cost/benefit return!
If $3 case holder & $20 .30-06 die does it for you, no need in more expensive equipment...
I ALWAYS come back around to the neck...
The ONLY reason for an 'Expander' ball is to drag brass up when the case has been excessively stretched, or if the neck sizer hole in the die is too small.
The big idea (and it was a HUGE idea!) Is when the ball enters the stretched & bloated case, the case is still stretched & bloated...
When you push swollen walls back in, the brass has to go somewhere.
When the stretched length is too long, and the shoulder in the dies pushes brass up, it closes down the neck a little.
It's metalworking basics.
When the case stretches in any direction, the brass gets thinner.
When the case is resized, the case walls can't get thicker, so the excess brass is forced UP, the only direction it can go...
When the shoulder is bumped back, the excess brass follows the shoulder in the die, moving up.
This closes down the neck hole right at the top bend of the shoulder.
The expander ball pulls that excess brass up into the neck where it can be trimmed away.
Guys that fire form, then neck size only have this figured out, they don't undersized the brass in the first place so it stretches even more on the next firing, so brass doesn't migrate nearly as much.
Orifice neck sizing (hole in dies that push brass back in to hold a bullet) is basically working a case that is chamber size, very little brass migration, neck sizing only required.
You chat get away with this if you are making ammo for different rifles in the same caliber, you MUST size the case, neck ball required to pull migrating brass up...
What I do recommend is seeing how far your necks are being crushed down!
Take the deprime/sizer ball out of your die, size a few cases and measure.
Most times you will be SHOCKED how much undersized the neck is!
This causes excessive work hardening and is a large contributing factor to neck cracking.
Honing out that neck in the die reduces the amount of crush, reduces work hardening.
If it's not broke, don't fix it..
If it's crushing like crazy, hone out that neck!
This takes a dead case, cut the neck off, drill out the primer/flash hole for a stick (wooden dowel rod) to pass through getting to the neck.
This dead case protects the rest of the die and serves as a guide for the dowel rod so you lap the neck out squarely.
Chuck up an appropriate size wooden dowel rod, sand the end down until it very tightly fits in the neck of the die.
Apply lapping compound, hone the neck a little...
When the dowel rod turns loose, cut the end off and sand down another tight fitting end.
Clean the die and test often, size a brass and measure the results.
The idea is to get a hole that sizes necks about 0.001" or so smaller INSIDE than your bullets.
Guys that want a little more bullet hold will want slightly smaller inside CASE necks and still let the sizing ball do its job.
Guys that want a little more bullet hold can chuck up the decapped/sizer ball rod and use lapping compound on the ball.
Be careful here, a little removal & measure/test!
Making dies fit YOUR rifle isn't fast, but it isn't difficult either!
. All three 308's are sized different and three of the AR's are sized different . I size on a single stage press and haven't adjusted my dies in years to size any of those cases regardless of how far I bump the shoulders . 
