Bullet Seating Question

[shcal]

I recieved my new Pac Nor barrel last week. I had the chamber reamed with a reamer I purchased from PTG with a spec'ed freebore of .085. the barrel is an 8" twist at 28". I want to shoot 75gr & 87gr V-Max and 105gr A-Max bulltes. I have started to establish seating depth and have noticed that when I set the bullets at the point where the ogive meets the lands everyone of the bullet bases is protruding past the neck/shoulder,n/s)area and into the shoulder. Here are my calculations taken form measured rounds follwoing the method I just described. As you can see, the adjustment required to set the base of the bullet .050 above the N/S places the bullet @ the ogive well into the lands. Am I doing something wrong in my calculations?

Bullet 75gr
Actual Dim. 1.719
Ogive to Bul. base 0.503
Diff. 1.216
To N/S 1.238
Into shldr. 0.022
Set N/S @ Zero 1.741
.050 to N/S 1.791
Into Lnds. 0.072

Bullet 87gr
Actual Dim. 1.764
Ogive to Bul. base 0.576
Diff. 1.188
To N/S 1.238
Into shldr. 0.050
Set N/S @ Zero 1.814
.050 to N/S 1.864
Into Lnds. 0.100

Bullet 105gr
Actual Dim. 1.768
Ogive to Bul. base 0.692
Diff. 1.076
To N/S 1.238
Into shldr. 0.162
Set N/S @ Zero 1.930
.050 to N/S 1.980
Into Lnds. 0.212

 

[Anmlsrdelicious]

An ancient chinese philosopher would say,,,"Sum ting wong". If your case is a 6br, and your freebore is .085, then there is no way you should be anywhere near the donut area with a 75gr bullet that is touching the lands. I have a 6br with a .060 freebore, and I can load 80gr bullets to touch the lands, and I am still well ahead of the donut area.

 

[Forum Boss]

You want the bottom of the bearing surface,full diam shank of bullet) above the neck-shoulder junction. Not so critical to have base of bullet above NS-junction.

If the bottom of the bearing surface,where the boat-tail begins) is above the NS-junction then you do have a problem.

On thing I've seen with brand-new barrels is that sometime there is a small chip or high point on a land that gives false readings on the throat length until it polishes out.

But eyeball your cases for us. .050" is roughly 1/16". If your full-diam. BEARING surface starts at least 1/16" above the NS-Junction you're fine.

Still, something sounds quite wrong. The 75 V-max has a very short boat-tail. No way that bullet should be coming close to the NS Junction.

Did you send JGS a dummy round. We've found that some die-makers have different methods of measuring freebore.

What's your cartridge OAL on the 87s, touching the lands. That will help me judge your true freebore.

 

[shcal]

On the 87 V-Max the OAL,from tip of bullet, not ogive) at just touching the lands is 2.234.

In each case that I gave you before the measurement of the bullet was taken from the lead ogive to the flat bottom of the bullet, not from the boat tail junction to full bullet diameter.

I did not send PTG a dummy round, I spoke to Dave about what I wanted to do, primarily shoot the 87 V-Max and he suggested the reamer with a freebore of .085".

 

[shcal]

UPDATE: I compared both the 75gr & 87gr V-Max as seated to just touching the lands and set bare unseated bullets next to them. On the 87gr it appeared that approx. .060" measured between the N/S junction and the bearing surface of the bullet, at just above the boat tail.

I believe, since I did not have an additional .243 Stoney Point bushing, that my mistake may have been to measure from the bullet's flat base behind the boat tail/bearing surface transition to the bullet's leading surface ogive. Does this sound reasonable?

 

[BoydAllen]

How are you determining the "just touching the lands" part? The reason that I ask is that it may be easier to work from jamb length,,the OAL that results when a bullet is seated so long that it is forced farther into the case when fully chambered, the length that results being referred to as the jamb length for that barrel, bullet, and neck tension combination) rather than touch which is much more subject to technique, and therefore more difficult to determine in a consistent manner. Have you seated bullets long in cases and chambered them to see what your jamb length is for each?

 

[shcal]

Boyd: The 87gr V-Max was seated as you described, bullet first seated long in case then placed into the chanber and jamed hard so that the bolt closed with bolt handle secured.

 

[Forum Boss]

On the 87 V-Max the OAL,from tip of bullet, not ogive) at just touching the lands is 2.234.

Sounds like everything is A-OK, though with the 105 Amax you may be getting close to the NS-Junction unless you go into the lands a ways.

The neck on a Lapua case is about .300. Using Quickload's bullet calculator, with a 87 V-max I measured at 1.045", with a cartridge OAL of 2.234", you will have .231" of bearing surface in the neck.

.300 minus .231 = .069" Just about right.

With the Amax 105s, a 2.350" overall length will put the bottom of the bearing surface .050" from the NS-Junction. See how close to that OAL you can get.

 

[shcal]

Moderator: Thanks for the double check, As soon as I break-in the barrel I'll report on the process, loads, accuracy and seating depths. Just waiting on my FL dies at this point. Have you got some good loads for for the 75gr, 87gr & 105's?
Thanks, shcal.

 

[Forum Boss]

Moderator: Thanks for the double check, As soon as I break-in the barrel I'll report on the process, loads, accuracy and seating depths. Just waiting on my FL dies at this point. Have you got some good loads for for the 75gr, 87gr & 105's?
Thanks, shcal.

For the 105s, 30.0 Varget for starters. IMR 4895 also worked well, with maybe 0.3 grains more powder. I saw some pressure at 30.5 Varget with naked bullets on hot summer days. With the 75s and 87s, consult our Varmint load page: http://www.6mmbr.citymaker.com/varmintloads.html

I'd start with VV N135 for those.