Precision reloading Redding micrometer die trouble

[Ldigio21]

I have been reloading for 50 years. Doing everything the way I always did. Over the last 6 months have tried to up my knowledge and game with precision techniques (Should have doe it years ago). Started measuring CBTO instead of COAL Using a Hornady Lock-N-Load® Bullet Comparator system off the ogive on my digital micrometer. There is a spread of 40 thousandths or more from cartridge to cartridge. If I adjust the seating even a few .0001s the outcome in CBTO is unpredictable spreading .0030 or more on the same cartridge .If I raise the ram more than once with out changing anything CBTO does not change so it does not appear to be variability in seating technique. This is for 280 AI with 160 gr accubond bullets. New never fired Petersen brass. I used an expanding mandrel so the case neck tension should be uniform.
Any help would be appreciated

 

[P7M13]

If I adjust the seating even a few .0001s the outcome in CBTO is unpredictable spreading .0030 or more on the same cartridge .If I raise the ram more than once with out changing anything CBTO does not change so it does not appear to be variability in seating technique.

I have experienced this same symptom. Part of your force needed to seat the bullet is being transferred to the shoulder and case body. It is then springing back. In the worst-case examples, you will bulge the shoulders or compress the case.
I can tell you it's related to multiple things:

• How well you case has been annealed.
• Neck web thickness
• The inside diameter of the neck after the expander ball has done its work.
• Bullet diameter

All of these have to be dialed in, and the force required to seat the bullet be very close to the same, every time.

 

[Wedgy]

Take the seating stem out of the die and verify that the tip of the bullet is not bottoming out in the stem and pushing on the nose instead of the ogive. They make a VLD seating stem for this reason.

 

[Varmint Hunter]

Cartridge OAL is irrelevant, other than to keep a cartridge withing the magazine limits. BTO is all I use when tailoring loads.

Several things may cause you to have a varied BTO after reloading. IMO The biggest two are excess neck interference (tension) and powder compression.

Just a few things to consider - good luck.

 

[M1A1ABRAMS]

I have been reloading for 50 years. Doing everything the way I always did. Over the last 6 months have tried to up my knowledge and game with precision techniques (Should have doe it years ago). Started measuring CBTO instead of COAL Using a Hornady Lock-N-Load® Bullet Comparator system off the ogive on my digital micrometer. There is a spread of 40 thousandths or more from cartridge to cartridge. If I adjust the seating even a few .0001s the outcome in CBTO is unpredictable spreading .0030 or more on the same cartridge .If I raise the ram more than once with out changing anything CBTO does not change so it does not appear to be variability in seating technique. This is for 280 AI with 160 gr accubond bullets. New never fired Petersen brass. I used an expanding mandrel so the case neck tension should be uniform.
Any help would be appreciated

 

[Ldigio21]

I watched this video a number of times and purchased the Hornady system and modified cases.Doing it about 30 times I got about 20 different readings . Some numbers came up a number of times so I have a rough guess that I can use . This is not the problem , It was inconsistent results from seating my bullets and getting significant variance in CBTO. I need to check the seating stem as per Wedgy's suggestion.

 

[Wedgy]

Doing it about 30 times I got about 20 different readings . Some numbers came up a number of times so I have a rough guess that I can use .

Do everything the same with the same amount of force ; make sure the modified case is firmly on the tool, push the case in all the way in the chamber firmly, even turn it a little back and forth to make sure it is snug. Push the bullets firmly into the lands(I use a cleaning rod from the muzzle to push it out), and I lightly push the head of the caliper against my bench which seems to give more consistent results than rolling the wheel alone.
As another mentioned be sure you are not compressing the powder as it can As another mentioned be sure you are not compressing the powder as it can push the bullets back out.

 

[Ldigio21]

Good tips all.I haven't been pushing to bullets with much force against the lands. They usually fall out without the cleaning rod trick. I have ordered the VLD seating stems and I think that will make most of the difference as COAL is closer than CBTO and that should not be.