reloading - case length to ogive 7mm

[officework13]

i am reloading some 7mm loads.
in particular the hornady 162sst and the berger 168vld hunting

i have loaded a blank casing (full length sized) bullet and pushed each into the rifle so the bullet would be pushed into the case so the ogive touches the lands.
i repeated this a couple times and came up with the same numbers for each of the bullets

however, there is a difference between the measurement to the lands between the berger and the hornady.

i am thinking i did something very wrong as my understanding is that i should be getting the exact same numbers. my understanding is the ogive is the ogive is the ogive and when it touches the lands, the measurement should be the same on every bullet tested. hence, test once and that measurement should be the same for every bullet.

i am using the hornady comparator guage.

thanks.

 

[txsendero]

Since the ogives of the 2 bullets are not exactly the same shape, your comparator bushing is probably touching each bullet at a little different place along the ogive.

 

[phutch30]

The ogives are certainly different. You should expect differnt measurements between bullet brands and bullet weights. Your seating depths will change accourdingly

 

[Kevin87]

For instance, my 7 mag measures 3.403 distance to the lands using the 160 gr Nosler Accubonds. With the Berger CH Hybrids, that measurement to the lands is 3.306.

 

[Corey Schwanz]

As said, different bullets with different ogive shapes will give you different results. The bearing surface of both bullets may be touching the rifling, but where the comparator actually touches and measures on the bullet from will be different from each other. Also, if you get a different comparator, you are likely to see different measurements as well.

But if you use the same comparator to measure the same spot on the any given bullet, you can have a good reference point to base future loads from as long as you stick with that bullet. When you change bullets, you have to re-measure to get a new baseline.

 

[Bart B]

Don't forget that the rifling erodes away .001" for every dozen or so shots fired. A .308 Win erodes .001" for every 3 dozen shots. That's how much further bullets have to jump to the rifling for a given load's fixed bullet seating depth.

A 7mm Rem Mag's rifling erodes away .001" for every 12 to 15 shots.