Ogive Measurment Differences

[PKT1106]

Hey guys-

I have been going through the 3rd Step tutorial from the pinned threads to find a good start length for my loads. I have both 175 SMKs and 155 Scenars. Last night, I went through and did some measuring and found the following:

175 SMK Ogive Length = 2.244"
155 Scenar Ogive Length = 2.236"

Now, I know everyone's chambers will be different, epecially in factory cut chambers. I am asking if these measurements are in line with what you guys have seen, with the Scenars shorter than the SMKs when measuring to the ogive.

Thank you

 

[waste_knot]

Here is a PDF form I fill in for all my match rifles.
This chamber shows 175SMKs
You can erase the data and use it.
That chamber from Accurate Ordinance measures 2.227 but my BD customs 308 measures closer to what you are getting.
I don't have any Scenars so I can't compare.

 

[Deadshot2]

Here is a PDF form I fill in for all my match rifles.
This chamber shows 175SMKs
You can erase the data and use it.
That chamber from Accurate Ordinance measures 2.227 but my BD customs 308 measures closer to what you are getting.
I don't have any Scenars so I can't compare.

Nice form. Of course my numbers will be a lot bigger as I have a Remington with a "tunnel" for freebore

 

[Heman]

Check where you comporator is mesauring. The stock stoney point measures on the bullet nose and since the noses have different shape you will get different measurements. I made myself some comporators guages that are 0.0005 under caliber size so I am measuring right on the ogive of the bullet. I now have consistant measurements regardless of bullets.

 

[PKT1106]

I am using the Hornady Comparator set with the .30 Cal insert on my calipers.

 

[Deadshot2]

Check where you comporator is mesauring. The stock stoney point measures on the bullet nose and since the noses have different shape you will get different measurements. I made myself some comporators guages that are 0.0005 under caliber size so I am measuring right on the ogive of the bullet. I now have consistant measurements regardless of bullets.

I just use the same comparator that I use when checking loaded OAL's. I don't measure to bullet tip unless I am going to use the magazine and want to make sure the round will reliably feed. Since it's all relative, I figure by using the same tool the results will be the same regardless of whether I am measuring from the design ogive or the "point where the bullet contacts the lands".

I've been previously using a 3x5 card with "Length to Lands", "Desired Jump", and "OAL with Comparator" for my various bullets.

FWIW, make sure to update your "Length to Ogive" measurements every so often. The hotter the loads the quicker the "Throat" will erode and your measurements will get larger, thus increasing the jump. Some barrels will "erode" more quickly than others as well as some calibers being more harsh than others.