80gn Projectiles Touching Lands

[Mechdraw]

Hello All,
Why is it so conflicting to get a consistent reading when a projectile is touching the lands, 223Rem.
Sierra 80GN MK's. New case, new projectile, firing pin removed and ejector removed. Insert projectile into case a short distance and insert into action, close dismantled bolt and check projectile for witness marks from rifling. Measure case to theoretical ogive,gauge made and mounted on verniers for readings), 3 assembled rounds,without powder, primer etc.) with readings within 0.07mm.
Hornady 80gn A-Max same procedure but very different readings, a variation of up to 0.29, that's close to 0.012'.
If cartridges were assembled with a variation of 0.012' in bullet seating depth you would think a lot of verticals would result, yes?
Why such a variation between projectiles? Am I doing it wrong?
The new cases were neck sized, throat opened and then run through neck bushing to get consistent neck size.

Regards

 

[janderson0]

I think you might have the bullets sticking in the lands, and when they release they will vary. I use the Lock-n-Load OAL tool, and use a cleaning rod to push the round out after the tool is locked. Some really stick in there. And I measure a few and use an avg.

Jim

 

[Mechdraw]

Thanks Jim, I understand what you mean. I will try it and see if my readings are more consistent.
Thanks again.

 

[Mechdraw]

I changed the neck tension, a lot less, as Jim suggested,,this was also stated to me on the OzFclass forum by AlanF) when I then inserted the cartridge into the chamber it was a lot more consistent, primarily because the projectile was not being jammed into the lands, again as Jim suggested, and in turn the projectile was not being pulled back out of the case which gave me a variation in length.
Thank you for the replies, I hope a few more are forth coming with different ideas that will make us all think about what and how we do things in our sport and hopefully improve our scores.

Cheers