Every bullet has different Ogive???

[stonehands1]

Ok so in an attempt to get my rifles as precise as possible I have recently purchased and oal guage and bullet comparator. My dumb brain thinks that when using the comparator along with oal guage that I should be getting the same measurement no matter what the bullet weight or design. It is after all measuring from a consistent point of thickness on each bullet. However this is not the case.
Any ideas?
Thanks

 

[climb-101]

all the bullets will be different if they are different weight or different manufactures.

 

[DocB]

Ok so in an attempt to get my rifles as precise as possible I have recently purchased and oal guage and bullet comparator. My dumb brain thinks that when using the comparator along with oal guage that I should be getting the same measurement no matter what the bullet weight or design. It is after all measuring from a consistent point of thickness on each bullet. However this is not the case.
Any ideas?
Thanks

Yes and no.

Yes in that the compatator is measuring each bullet at the same point on the bullet where it reaches caliber width, the ogive, which is where it should contact the lands. No because due to the bullet form, length, weight the beginning of the ogive will be at a different location from bullet to bullet, sometimes even within the same lot of bullets.

Hope this helps.

DocB

 

[FearNoWind]

DocB probably said it as well as anyone can.

 

[RonS]

Couple the above with the fact that all comparitors are different and most will not match the chamber of any given rifle with any degree of precision. The comparitor is a relative measure. That is why you must use the same comparitor when measuring the distance to the lands in any given rifle with any given bullet.

 

[bob4]

+1 on what DocB said. I have this happen with the same box/lot of bullets. always a difference of .001- .002.

 

[Corey Schwanz]

Within a box/lot you should hope to not see more than a couple .001s variation. Different lots can have wider spans (made on different dies, etc). Different weights and especially different brands of bullets, the comparator measurements will likely be no where close to the each other.

Also, don't get a 2nd comparator and try to confirm it with the first. 2 comparators could get a different reading on the same bullet as they may be machined slightly different from each other and contact a different spot on the ogive.

 

[stonehands1]

I think I just figured it out. The comparator hole is less than .308 probably .300. This is why bullets with different Ogives fit my rifle differently. Am I right?

 

[DocB]

I think I just figured it out. The comparator hole is less than .308 probably .300. This is why bullets with different Ogives fit my rifle differently. Am I right?

That's correct. The lands are normally .300 (hence .30 caliber) which is where the ogive makes contact; and the grooves are .308 caliber, which is the barrel full diameter. Your comparator will size the ogive at .300. By fitting your rifle differently, I'm thinking you mean 'further down' the bullet from the tip, or more correctly said, the ogive is further down the secant from the tip. This would be reflected in different seating depths and COAL for the same caliber bullet but in a different configuration, i.e. a VLD or Hybrid .30 cal bullet versus a .30 cal Scenar or Match King, or for the same style bullet in a different weight. A bullet in the same caliber that is heavier is 'longer' by necessity. In most cases this normally relates to a higher BC and a more stable (increased sectional density) but slower bullet at longer ranges.

You're on the right track sir, keep at it and soon all of this reloading 'magic mumbo-jumbo' will all fall into place.

Have fun!

DocB

 

[climb-101]

I think I just figured it out. The comparator hole is less than .308 probably .300. This is why bullets with different Ogives fit my rifle differently. Am I right?

the comparator size is just for giving you a place to measure that is close to a given bullet diamiter and let you measure that same diamiter on all the bullets on that given size. the bullets can be different shapes though and that will move that given diamiter up or down on a bullet.

here is a picture of 2 different bullets "A" and "B". the lines represent where the ogive is and also where a comparator would hit the bullet. if you had your press/die set up for bullet "A" to have a .010" jump to the barrel and switched to bullet "B" it would still have a ".010" jump but it would have a longer OAL because the ogive is further down the bullet because of the shape. if you measure just the bullets from the ogive to the base they will also be different even though they are the same length from base to tip.

 

[stonehands1]

Thanks for all the help. Makes sense now.