I think you might have stumbled on to the problem, something sucks.
Leaning toward brass, but it could be the measuring device, might be the operator.
.283 & .286 make sense a.003” interference is not un common.
.286” less .257” leaves brass .0145” thick. A bit much for my taste but no big deal.
The problem is .290” fired and any tension at all from the bullet slipping in. You have .002” clearance. This assuming the inside diameter is consistent.
There is a phenomenon known as a donut that form inside the neck and shoulder junction. This can cause the bullet to be pinched in the case and cause a pressure spike.
You might be able to feel when the bullet hits this tight spot. The bullets you are using will be ideal for this, they will possibly ratchet down and basically click every time a grove passes the tight spot. I think if you solve why .002” of clearance requires any force other than gravity to drop the bullet into the case, you might be able to move forward.
Double check your numbers, but I would certainly give this some attention.
I would add that comparing case capacity of the hornady and Alpha brass could provide another clue.
dellet:
I understand where your philosophy is at!!!
Lets take a stroll back in time!!! This is going to blow your mind!!!!
In the old BR days of NECK SIZING ONLY, Bonanza/Forster made inside neck reamers that fit in the Forster Hand Crank Trim Lathe!!!!
The reamers were tool cut to +.0010" to +0.0015" of bullet diameter!!!!
The Once Fired, Full Fire Formed brass, with full blown out necks, were inserted into the Lathes collet (based clamped) while centering the chamfer cutter into the blown out case mouth!!!
The secret to inside reaming is to never stop turning the tool and lightly forcing the cutter into the case!!! If it start binding, slowly withdraw the turning tool!!! Clear the chips from the cutter with a small paint brush!!! Start cranking and work slowly into the case again and don't stop turning the tool!!! Keep working in and out unto you have cleared the neck shoulder junction!!! Keep cranking as you withdraw!!!
THE REASON TO KEEP CRANKING WHILE THE TOOL IS IN THE NECK, IS TO AVOID 6 SCORE CUTS IN THE NECK WHICH COULD LEAD TO NECK CRACKS!!!
For BR shooters, at that time, this prep work was great!!!
PLUS, YOU COULD INSIDE REAM, AND TRIM AT THE SAME TIME!!!!
But in the situation that the OP wants, it is also great!!!
Having 0.0010-0.0015" clearance is great for BR reloading Hunters!!!!
Extra neck tension is required for the near max, to max loads for hunting!!!
I've done this for Rem 700 actions in a BDL varmint special(7-08), VLS in 22-250, and a custom rifle (air gauged barrel) in 25-06!!!! All this rifles shoot less than 0.2MOA!! And all are personally tuned hunter/varmint rifles!!!! The 7-08 (160gr SGK SBT) shot a 7shot group of 0.092MOA from the bipod, squeeze bag, prone position!! Tight cloverleaf!!!!
Now, the OP has a family!!! Family comes FIRST!!
To ease your mind dellel, and cut expensive tooling for the new OP reloader, I'm offering assistance for the OP to send me 10 fired, (not resized) cases!!! I'll record the before and after measures!!! Then send the cases back to the OP!!! I'LL GUARANTEE THAT THOSE 10 CASES WILL BE HIS FAVORITES!!!!
Plus, with minimal neck clearance, the OP doesn't need to anneal the neck shoulder region!!! Another cost saver for the new reloader with family!!!!
dellet:
This will hopefully satisfy one of the issue you are worried about!!!
By the way, isn't bumping with FL dies a modern day verses of modification of BR Neck Size only until it can no longer chamber, where the BR shooter bumped the shoulder back a bit with FL dies?????????????????????