9MM conundrum

[Redneck]

I have a goodly amount of 147 grain cast TC 9MM bullets and have been trying to work up a load. My Lyman cast bullet book said that Blue Dot gave the highest velocities with this bullet, so that was where I started, then the problems started. The sized cases (all range brass) were given a sufficient case mouth flare to accept the cast bullets without shaving lead, and had no issues in that regard. The loaded rounds had a C.O.A.L. of 1.054-1.058" checked right after seating the bullets, then they were crimped with  a LEE FCD and shot for functionality. The load was 5.5 grains of Blue Dot, right in the middle of the load data and the primers of the fired rounds were completely flat. I tried another 5 rounds using the same load procedures only I cut the load back .2 of a grain (5.3 grains) did the same exact load procedure and I was still getting flat primers. I walk away from the loading bench scratching my head trying to figure out whatinthehell is causing this, and come up with nothing. After a while I go back to load 5 more at the reduced charge, go through the same loading procedures except that I check the C.O.A.L after crimping and the measurements are from .022-.030" longer than what I checked them at after seating the bullets. I now know what is causing the flat primers, the bullets are being forced into the rifling causing the high pressure. I know how, I just don't know why or how the rounds can be increasing their length by simply adding a crimp.
Today I'm back at it with two different taper crimp dies, one is mine a 38/357 taper crimp die and a 9MM taper crimp die that I borrowed from a friend, both of these are Redding. I also changed the seating plug to the type for round nose bullets and the seating depth/OAL lengths became more consistent even though I'm loading truncated cone bullets and the other replaced seating plug was designed for flat nose bullets (?). Now I'm thinking everything is in order to test these new loads, the loading procedures have been double checked for any errors, the C.O.A.L. is 1.052-1.056", crimped with the Redding die and double checked for length, I should be ready to shoot them. I re-checked the C.O.A.L. and a couple  of them have grown in length while sitting in a cartridge block on my loading bench, they have increased their length by .009" and .012" WTF? They are different brass makes, one a WCC mil-spec case and the other a Blazer. One of them, the longer of the two I have re-seated the bullet 4-5 times and it keeps going back to that +.012" length.  Does anyone out there in reloading land have any idea what is or might be causing these foibles?

[Trapper6L]

Here's more for you to consider. Blue Dot doesn't really perform well until it hits close to max loads, you are on the bottom of the book. You are also at a compressed powder charge for the powder/bullet combination. Most likely the powder being compressed is pushing the bullet out of the case. You are attempting to crimp a cartridge that head spaces on the OAL of the case at the case mouth- a major no-no. You do not crimp 9mm ammo. The bullet is held in place by neck tension only. You should have somewhere around 40lbs of neck tension. You're probably not getting there with your dies. It's been my experience with 9mm that the brass can be an issue too. Some of it is heavy walled while others are thinner than paper. Current manufactured Winchester comes to mind for being thin. Thinner brass means less neck tension. I would strongly suggest saving the Blue Dot back and using a faster burning powder. Power Pistol by Lymans node is their accuracy load. I've found over the last 50 years of reloading that their accuracy loads are on the money. Velocity is close to the same.
If you just want to be adventurous you can increase neck tension by taking 00 steel wool and running the expander plug in a drill and take off about .001, is where I would start. The biggest issue you'll run into is if you end up with heavier walled brass, neck tension will go up and it can leave a ring on the brass at the base of the bullet after the bullet is seated. I've not had any issues with it accuracy wise or functioning of the gun but it looks ugly. Just so you are aware before you change the expander dimensions.

[Redneck]

I've read your post and will give it all some consideration, however my problems/issues are not with the Blue Dot powder.  The original issue was what is/was causing the cartridge to increase it's length by as much as .030" when applying the taper crimp. Yes the 9MM does require a crimp after the bullet seating, all pistol cartridges require a crimp, be it a taper crimp on auto pistol cartridges or a roll crimp for revolver cartridges if the bullet configuration allows that to be done.
I thought about powder compression or neck tension causing the loaded rounds to grow as you said, but the loaded rounds have a neck diameter of .3765-.377",  under recommended neck/mouth diameter of a loaded round. The Blazer brass is about .001-.0015"thinner at the mouth than the WCC brass, usually this doesn't create issues when loading ammo. The last variable I can think of is maybe the bullets themselves, there is some length variation by as much .012-.015", but those that I've checked the diameter of all fall between .3558-.3662". I may end up melting all of these down and casting my own from the salvaged lead alloy. So far I haven't had any issues with my home cast bullets.