If you have pulled 173 bullets or even new ones you will see a big variation in how the bases are formed. The third bullet from the left is a perfectly formed base and will be best for 600 yards and beyond.
Note how the lead is nice and uniform below the rolled radius of base of bullet? That is what you are looking for.
Bullet base uniformity is critical in long range applications.
A ammo tech from Frankford Arsenal put this tidbit on me about 25 years back. You can prove it yourself. Select 10 bullets like the one on the extreme right and ten like the one 3rd of left. Load them with same load and shoot for dispersion. You should see a much smaller group from the ones that look like 3rd from the left.
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