What has happened over the years with the Blackout cartridge is largely operator error, but also due to trusting published data and new components. Many 308 bullets can not be loaded to magazine length. What has come up a few times is people unknowingly jamming bullets.Suputin221 wrote: ↑Sat Dec 28, 2019 5:21 pmWhile the benchers guys made a thing out of jamming bullets into the lands, that is not a good idea for most of us. Once had an issue where I ejected an unfired round and left the bullet in the throat. That wasn't the worst part though. The case spilled ball powder into the bolt locking lugs and action. Basically the result was an inoperable rifle. Ball powder is just nasty to try to clean out of locking lugs and it very effectively prevents the bolt going into battery properly.
Thus we should always shoot for at least some jump to the lands.
I have measured many new factory cases and found at least a .020” variation in base to datum length. A few that would be less than minimum headspace, many that would be more than maximum. A cartridge made with base to ogive set to .010” off the lands, that has the shoulder set too short or even minimum spec, can headspace off the bullet. Fiocchi had a run like this, I think ADM also did.
Same thing happens if you bump the shoulder of fired brass .002-4”, set the bullet .010” off the lands and then use the same base to ogive length with new brass.
Many people check base to datum on the case, and base to ogive on the bullet. Those numbers generate datum to ogive. That number has helped diagnose enough unexplained pressure problems for me that I at least pay attention to it.
Just another number that has meaning and can be helpful at times to know.