seating depth and ogive measurement method differences

[rpl6cm]

I am having a very big issue and I wonder if there is someone out there to help me. I am shooting a 6.5 x 47 lapua with a bat action, Shehane MBR stock and 28" Bartein barrel. The problem is in the seating depth. I have shot Lapua 123s, Berger 130s with acceptable results at 100yds. 123s moa .280, 130s moa .386. My question is, am I using the wrong method of measureing to the ogive. i am convinced, maybe wrongly, that the best way to measure to the lands is by measure to the ogive and forget about the coal. The ogive would seem to be the most stationary data point on a new barrel.

I have tried three different methods, with once fired cases, same bullet for each weight and got three different lengths. I need help to teel me where I went wrong.

First method was with a Sinclair seating depth gauge. Second method is with a prepped case(fired once from my rifle and then threaded at the pocket. Third method is with a split-neck case I prepared with just enought tension to move the bullet with effort.

The measurements come out all different. I thought they should be similar, I'm not sure what method to use and why they are not the same.

coal ogive
bullets lap123gr, lap139gr, berg130gr lap123, lap139, ber130
method
sinclair 2.769 2.735 2.81 2.132 2.107 2.104
split-neck 2.073 2.106 2.075
hornady 2.739 2.726 2.789 2.107 2.098 2.078

could someone tell me what would be the most accurate point to measure against, and why these methods differ. I know ther are some brain-stormers out there. Thanks

 

[watercam]

I measure at least three times (usually more) to make sure I am consistent. Assuming you are using a comparator to measure the ogive you should be getting consistent results with either tool. I think the Hornady tool is the most accurate myself. Are you sure that the calipers are completely flush with the bottom of the case AND the surface of the comparator? That error is good for .010" or more.

 

[rpl6cm]

thanks for the response. yes i do use a sinclair comparator on all the bullets. i try to make sure the base is flat to the point i sometimes use a mic base holder. all these measurements are without the base holder. i may have to try this all over with the base, but i am pretty anal when it comes to these measurements, that's why i'm stumped. thanks again for the help.

 

[Rust]

Consistancy is the key to the whole thing. Using the same amount of pressure to hold the case in the chamber and the same amount of pressure to seat the bullet. The problem with the little rod that locks in the Stoney Point/Hornady tool is that it is a little flexible and can be a little bowed from too much pressure seating the bullet. The other thing is that not setting the lock screw with the same pressure each time can cause variances as well.

Practice may not make perfect, but it can improve things.

 

[JRinCo]

The Hornaday tool is the only one that I know of that gives consistent results. I bought the Sinclair tool 25 years ago, I couldn't make it work (maybe I'm to clumsy). Nor can I get consistent results using a fired case. When the bullet makes firm contact with the throat, it sticks there, maybe a little maybe allot. When you withdraw the case, the bullet doesn't come along consistently.

If you have the Hornaday tool, you normally get good results. But even this requires some practice. When you use it, all that you want to do is make the bullet touch the rifling with the same amount of pressure every time. That's the measurement that you want (bullet touching the rifling). If you use more pressure you're pushing the bullet beyond the contact zone and you will not get consistent rusults.