The tracking distance is too limited to correlate to any BC’s at distance, where BC really matters. It could give you an idea of your MAX BC, but as velocity falls off over distance, so does your BC. Sort of in line with Sierra showing BC’s over different velocity ranges. You could get some...
Yes to GordonsGarage’s comment. If the tension or burrs are not this issue, do what he said with lapping compound. I do not recommend the sandpaper method for anything other than knocking a burr off the circumference of the stem.
If you have loaded this bullet without the ring before, don’t do this....I have jumped the gun on things like this before and have been stuck buying new equipment.
This could be a viable issue as well. Can’t see really well, but it appears the case mouth shaved a little copper off the bullet in your first picture. If so, add more inside neck chamfer
Take a bullet and fit it with both your stems out of the die. The stem it likes will show little to no wiggle, but I would explore neck tension if you have loaded this brass and bullet combo without issue before
I wouldn’t dive right into a custom stem. I feel that is like throwing parts at a vehicle when you don’t know the exact cause. Determine the cause, then remedy.
Measure the outside neck diameter with your calipers before and after seating a bullet for neck tension just to calibrate your bushing calculations. Spring back from work hardening will cause you to need to go to a larger bushing as you continue to reload a case over time if you do not anneal
One possibility is too much neck tension. Another is a cracked seating stem. Take your stem out and give it a hard look with a flashlight looking for anything from a large crack to a hairline crack.
Make sure you have properly adjusted the diopter. There are some posts on it.
1) Set to Max Power
2) Parallax set to Infinity (this is very important)
3) Point it at a solid, light background like a white wall or blue sky. You don't want anything except a solid, light color to look at.
4) Start...
Wet tumbled my 30-06 brass I shot last weekend as well as a huge pile a range pickups in various calibers. I think I wore off my fingerprints match prepping all the brass.
I have tons of various head stamps sorted by head stamp. New and once fired, match prepped including primer pockets uniformed, flash holes deburred, etc. New unprimed LC without crimp, new Winchester, lots of once fired processed
I would start at the starting charge for the 150 with H4831 and run a pressure ladder. 4064 could work, but probably a little fast for that heavy for caliber projectile. Another option is call Berger, they are very helpful.