This little Ruger shooting the short 125gr Speer projectiles was proving enigmatic. Sometimes it would shoot exceptionally well, other times not so. I finally cracked the secret to achieving a consistent reload; <DRUM-ROLL> "And the winner is, NECK TENSION!".
The lee collet die mandrel was sized to around .306". Neck sizing was only resulting in around -0.001" to -0.002" of neck tension. The 125grainers paired with the rather aggressive Lil'gun and a very long throat (to cater for exceptionally long, heavy subsonic pills the 300aac is kinda designed for) was yielding poor accuracy. But only on with fireformed brass sized by the Lee Collet Die. My guess is this is likely due to inconsistent ignition. And I can't rely on the lands to halt the pill, as it is miles away. Nope I needed a very tight neck.
I systematically turned the mandrel down to .304", yielding aproximately -0.003" of neck tension, and now she is shooting into well under moa for at least the first 5 shots. A crimp would likely have a similar effect, but as discussed above, I much prefer the non-destructive and controlled collet die over a secondary.
- Muzzle brake, m1907 sling
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