Thread: Olive length changing?

One thought...
SAAMI specs for 308 say lands at 7.62mm and grooves at 7.82mm. So I assume this means 308 projectiles are actually greater than 7.62mm diameter, otherwise you won't get any rotation from the rifling. .308 of an inch is actually 7.82mm
If your comparator insert is 7.62mm (or anything less than 7.82), it is actually contacting just before the true end/start of the ogive, and how far before the ogive will be affected by projectile shape. And the insert has to be at least a bit smaller than bullet diameter or it could travel the full length of the projectile and you wouldn't be able to get a meaningful measurement.
In effect, you are probably measuring where the projectile diameter equals the diameter to the lands, not the true ogive point. But that is what you want anyway to be able to set your jump so all good, but the measurement will vary slightly between projectiles.

Originally Posted by Gibo

I think you have COAL and Base to Ogive mixed up? The COAL can be the same for any given projectile if you choose to seat it as such but the Base to Ogive will change depending on the projectile shape. Your lands cant move as they are part of the rifle but due to bullet shape the distance to the lands can vary even if seated using the same base to [bullet tip] measurement

I think adding olives was a complication too far.

[QUOTE=Cigar;753157]One thought...
SAAMI specs for 308 say lands at 7.62mm and grooves at 7.82mm. So I assume this means 308 projectiles are actually greater than 7.62mm diameter, otherwise you won't get any rotation from the rifling. .308 of an inch is actually 7.82mm
You are over thinking it, 7.62 is the bore diameter and 7.82 is the groove diameter in English/American .300" x .308" as you can't get .300" diameter bullets don't worry about it,
Just start with the bullets seated to Manufacturers specs and tweak from there, The ogive measurement is variable any way manufacturing tolerances being what they are there can
be a spread of .003" or more between bullets, The only way to get them all the same is to measure the base to ogive on all bullets and batch them, That gets boring very fast, unless you are OCD
If you are trying for a world record group at 1000 yards Ok, anything else it's a waste of time