Is there a minimum amount of projectile that should be seated in case neck?

[goinghunting]

Is there a magic amount you guys are after? I know it varies a ton on cartridge and bullet, freebore, but say with 6 CM or 6.5 CM.

Like say on my 6 CM Proof pre-fit if I want to run the 110 MK about .020 off the lands only about half of the neck has bearing surface of the bullet making contact, and to run the 110s bearing surface down to the neck/shoulder junction I need to jump about .180-.200...

Where the 108 ELDM can be .020 off the lands and have almost the entire neck in contact with the 108s bearing surface.

Is there a sweet spot you try to get to?

FINALLY, What I'm getting at-

In my mind more of a donut could be formed if the entire neck does not have bearing surface of the bullet making contact on ignition.

Am I looking at it wrong?

 

[30cal user]

Here's a definition of the 'ideal bullet position' from Robert Whitley's description of his 6mm / 6.5mm SLR designs.

http://6mmar.com/Super_LR.html

Note: When the term "Ideal OAL" is used, it means the junction of the boat tail and bearing surface of the bullet is forward of the junction of the neck and shoulder of the case by about .025" or so. When the term "Forward in neck but good OAL" is used it means the junction of the boat tail and bearing surface of the bullet is forward of the junction of the neck and shoulder of the case by about .040" - .070" or so (depending on the bullet involved) which is still good because the cartridge neck is .322" which means you have about .250" plus of neck still holding onto the bullet.

 

[30cal user]

You can ascertain this two ways. The quick and dirty way is to seat a bullet gradually deeper in a sized but unprimed/uncharged case and put the same model of bullet alongside on the bench with the tips level to see where the shank/shoulder junction lies in the case and judge that ~0.025" gap by eye using calipers set at that value to give a guide. When you're there, then measure the resulting COAL and see how that matches your magazine and/or rifle chamber freebore.

The other (more scientific) way is get a drawing of the bullet - as in this drawing on Berger Bullets' website of its new 156gn EOL Hunter:

https://bergerbullets.com/new-berger-6-5mm-156-grain-eol-elite-hunter/

and see where the tail to shank junction lies - ie take the quoted OAL and subtract the tail length, 1.512 - 0.189 = 1.323" from the junction to bullet meplat (tip).

Then take that value and subtract the case-neck length. (But first measure the OAL of the case you're using - you'll need it later.)

1.323 - 0.259 = 1.064" for the Creedmoor. That amount of bullet should be visible outside of the case, but we want that 25 thou' of clearance between the two junctions so add that back in to the bullet outside of the case-mouth:

1.064 + 0.025 = 1.089"

You then take that value and add it to the case OAL. The 6.5mm Creedmoor at its maximum SAAMI length before trimming is 1.920". so let's assume your case is exactly that. Add this figure to the calculated one for the bullet to get the cartridge OAL (COAL) for that bullet seated at the optimum position in a Creedmoor case.

1.920 + 1.089 = 3.009" ........... over SAAMI max COAL but no surprise for this very long / heavy bullet.

You then have to reconcile this to the rifle chamber and / or the maximum COAL that the magazine will feed reliably.

 

[30cal user]

This is taken from another forum and forum member

 

[goinghunting]

Thanks @30cal user , the "quick and dirty" way you described above is what I have always done, and has always worked good enough for me.

Not really sure why I started questioning it or thinking about the donut that can form at the neck/shoulder...