New Reloader with detailed COL numbers looking for double check

Moderators: gds, bakerjw, renegade, bamachem

User avatar
dellet
Silent But Deadly
Posts: 6355
Joined: Fri Nov 30, 2012 1:25 pm

Re: New Reloader with detailed COL numbers looking for double check

Post by dellet » Sat Dec 28, 2019 10:49 pm

Suputin221 wrote:
Sat Dec 28, 2019 5:21 pm
While 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.
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.

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.
300 Blackout, not just for sub-sonics.

BulletFlight for Android
Suputin221
Silent But Deadly
Posts: 338
Joined: Thu Dec 22, 2011 9:03 pm

Re: New Reloader with detailed COL numbers looking for double check

Post by Suputin221 » Sun Dec 29, 2019 2:35 am

I don't buy factory ammo. I only reload.

As the bullet seater sets loaded length from base to ogive and my OAL gauge measures base to ogive, it would seem obvious to just use those two values. I've really never considered calculating the datum to ogive value.

User avatar
dellet
Silent But Deadly
Posts: 6355
Joined: Fri Nov 30, 2012 1:25 pm

Re: New Reloader with detailed COL numbers looking for double check

Post by dellet » Sun Dec 29, 2019 4:08 pm

Suputin221 wrote:
Sun Dec 29, 2019 2:35 am
I don't buy factory ammo. I only reload.

As the bullet seater sets loaded length from base to ogive and my OAL gauge measures base to ogive, it would seem obvious to just use those two values. I've really never considered calculating the datum to ogive value.
It only matters if you’re loading just off the lands and minimally sizing brass, but you’re right, the bullet seating die and the overall length gauge don’t care where the shoulder is. The rifle chamber does.

The base to ogive length isn’t what keeps the bullet out of the lands until it’s too late. The case stops in the chamber on the shoulder, at least it should.

It’s a measurement that most people will never need, but Understanding the relationship and distance between shoulder datum and bullet ogive is something anyone who loads should understand.
300 Blackout, not just for sub-sonics.

User avatar
rebel
Silent But Deadly
Posts: 7239
Joined: Mon Apr 22, 2013 2:01 pm
Location: Moonshine Country

Re: New Reloader with detailed COL numbers looking for double check

Post by rebel » Sun Dec 29, 2019 4:14 pm

Ask any guy shooting IBS of F Class if they use that measurement. Hell, those guys trim their fingernails the same length before a match.
I would recommend adding that to your log data.
You can't beat the mountain, pilgrim. Mountains got its own way.

Post Reply