Bullet Seating Depth Measuring Problem - Touch, Jamb, or ?

[thermaler]

I must say I have never been impressed with the old Stony Point seating depth measuring device, that is now called the Hornady LNL device. There is many tolerances that can skew measurements as you are finding out. IMO the best thing you can do is sell this tool. The Sinclair depth finding device is not much better, though it takes out many of the variables found in the Hornady device, my experience is that it just doesn't come up with a correct seating depth.


What I have found to work best ot using a fired case that has been sized, and will tightly hold the bullet. One variable you may be seeing is you need to segregate your bullets by Ogive length. In a typical box of 100 Sierra bullets it is not uncommon to find two different ogive length bullets. Once you have this figured out you can proceed, to find actual seating depth is a tedious and time consuming process. You want to start with the bullet seated just into the case, (WITH NO PRIMER OR POWDER!!!!) and then place it into the gun, and close the bolt. then remove the case, and measure it. Now place your seating die to that measurement, and then taking the bullet clean the marks off with some 0000 steel wool. now move the bullet in at .002 increments, and watch the marks. At first the marks will be rectangular, and this is a hard jamb. when you back the bullet out you will see the marks change, when the marks are square, this is close to jamb, then as you move out you will see the marks be crisp at the top, and fad at the bottom, this is close to touching. It takes many times of moving the bullet in the case and reinserting the case to find this measurement. When I look for is at the point where the marks are hardly visible, this is just touching, and this is where I start looking for a seating depth. From this point I will make loads with the bullet .005, .010 , .015 , 1nd .020 off from this measurement.

Bullet seating depth is THE most curtail thing to accuracy, and spending time to get it right is well worth the effort.

I'm having a bit of trouble following the rectangular/square marks thing--any illustrations/photos to help more easily understand? thnx.