Try Rotating Cases During Bullet Seating to Reduce Run-Out
Here is a simple technique that can potentially help you load straighter ammo, with less run-out (as measured on the bullet). This procedure costs nothing and adds only a few seconds to the time needed to load a cartridge. Next time you’re loading ammo with a threaded (screw-in) seating die, try seating the bullet in two stages. Run the cartridge up in the seating die just enough to seat the bullet half way. Then lower the cartridge and rotate it 180° in the shell-holder. Now raise the cartridge up into the die again and finish seating the bullet.
Steve, aka “Short Range”, one of our Forum members, recently inquired about run-out apparently caused by his bullet-seating process. Steve’s 30BR cases were coming out of his neck-sizer with good concentricity, but the run-out nearly doubled after he seated the bullets. At the suggestion of other Forum members, Steve tried the process of rotating his cartridge while seating his bullet. Steve then measured run-out on his loaded rounds. To his surprise there was a noticeable reduction in run-out on the cases which had been rotated during seating. Steve explains: “For the rounds that I loaded yesterday, I seated the bullet half-way, and turned the round 180 degrees, and finished seating the bullet. That reduced the bullet runout by almost half on most rounds compared to the measurements from the first test.”
READ Bullet Seating Forum Thread »
Steve recorded run-out measurements on his 30BR brass using both the conventional (one-pass) seating procedure, as well as the two-stage (with 180° rotation) method. Steve’s measurements are collected in the two charts above. As you can see, the run-out was less for the rounds which were rotated during seating. Note, the change is pretty small (less than .001″ on average), but every little bit helps in the accuracy game. If you use a threaded (screw-in) seating die, you might try this two-stage bullet-seating method. Rotating your case in the middle of the seating process won’t cost you a penny, and it just might produce straighter ammo (nothing is guaranteed). If you do NOT see any improvement on the target, you can always go back to seating your bullets in one pass. READ Forum Thread..
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Tags: Bullet Seating, Concentricity, Die, Reloading, Run-Out, TIR
Simple, cheap (free!) and can make a measurable difference in run-out. Brilliant.
Good info. Falls under nothing ventured-nothing gained. It works for me!
I’ve been rotating my ammo 180 for years but after I have allready seated the bullet on the first stroke. Does it matter that much to seat the bullet 1/2 way before you turn it 180?
Fully seat the bullet. Then turn it 90 degrees and fully seat again.That will split any run-out by exactly half.
Turning 180 degrees will put the run-out to the other side, not split the difference
I started the practice of rotating about 2 years ago. My technique is different however. I do 3 steps, split the seating and rotating into 1/3’s. It has reduced my TIR by over 50%.
I start with very straight case necks (less than 0.001″ TIR). Runout was running as high as 0.005″, now everything is basically less than 0.002″.