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Old January 10, 2017, 09:11 PM   #1
Bytesniffer
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Join Date: November 29, 2016
Location: Long island ny
Posts: 59
Using nosler 7.62x51 data as reference.

The 7.62 data shows a volume of
49.5 gr of water
My fire formed 7.62 round
Trimmed to factory length 2.0075
After firing the round
Reads 52.3 grains of
Of water.
Nosler shows a length
Oacl of 2.800 with a 155 grain bullet
Powder charge of 40.5 in
For imr 4064. What Inn using.

If I read the coal of my 7.62 round
It reads 2.784
Bullet is 150 grain. 1.125/6 in long.

If I take my fire formed case
With neck tension on it and take the
Exact bullet that factory ammo is using
150 gr BT 1.125 in lenght and put this bullet
(Dummy round ) load it in my chamber
And close it. I force the bullet
Into the case and bullet ogive hits
My lands .
It reads 2.834.

So I'm using 40 gr of
Imr 4064 150 gr bullet
Coal 2.785

These rounds should be fine
Just like factory spec 7.62
Ammo I have.
Then , I will increase to 2.790
Next time. Then 2.795 that's still
Approx 40 thousandths from ogive
To lands.
See how they perform.
In my rifle case and bullet
Hits the lands at 2.834
I have room to move closer ?
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File Type: jpg 762-155.jpg (49.7 KB, 8 views)

Last edited by Bytesniffer; January 11, 2017 at 08:12 AM.
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Old January 11, 2017, 08:55 AM   #2
Mobuck
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"These rounds should be fine
Just like factory spec 7.62"

No reloaded round "should be just fine" unless you have followed the rule of "start low and work up".
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Old January 11, 2017, 10:32 AM   #3
jwrowland77
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Location: Conway, Arkansas
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Quote:
Originally Posted by Mobuck View Post
"These rounds should be fine

Just like factory spec 7.62"



No reloaded round "should be just fine" unless you have followed the rule of "start low and work up".


Mobuck, if you noticed, 40gr is about .5gr under minimum. It's not like he's starting at max.


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Old January 11, 2017, 11:48 AM   #4
Unclenick
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Location: Ohio
Posts: 12,968
Bytesniffer,

You have to keep the two water capacity standards separated:

Case Water Overflow Capacity (CWOC) is capacity for water with the case filled to level with the mouth. This number is used with QuickLOAD.

Case Water Capacity (CWC) is the amount of water space remaining after seating the bullet into the neck. This number is used together with powder bulk density to determine load density.

If you have CWOC it is pretty simple to use seating depth to determine the CWC.


Seating Depth = Case Length + Bullet Length - COL


For a flat base bullet, where:

lengths are in inches

r= ½ the bullet diameter in inches

253.5 converts cubic inches to grains of water volume at 73°F (room temperature average in many places).

CWC = CWOC - (Seating Depth × pi × r² × 253.5)


For a boattail bullet you will additionally have to add back the difference between the volume of the boattail and a cylinder the same length.

Where:

l is the length of the boattail in inches

r is the diameter of the bullet in inches

R is the diameter of the heel of the boattail (the bottom diameter):

Add back volume = 253.5 × ((l × pi × r²) - (l × pi × (r² + R² + (R × r)) / 3)


Nosler's 49.5 grain number is about right for CWC with their bullet seated to their specified COL. CWOC is usually more like 55-56 grains in 7.62 cases.
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Old January 11, 2017, 12:50 PM   #5
T. O'Heir
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Location: Canada
Posts: 7,078
You're over complicating the entire thing. You don't need to fiddle with case water capacities at all.
"...Trimmed to factory length 2.0075..." 7.62 x 51 is loaded using .308 Win data. Trim-to for .308 is 2.005". Mind you, the 2.5 thou won't make any difference.
2.800" is the Max OAL for .308 Win with any bullet. You can forget the 'off-the-lands' stuff until you have worked up a load too. Just use the 2.8" and you'll be fine.
Don't know what No$ler bothers with separate data for 7.62NATO either. Or why they mention SAAMI. 7.62NATO isn't a SAMMI spec. NATO specs have nothing to do with SAAAMI anything. Nobody else provides NATO spec data either.
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Old January 11, 2017, 01:00 PM   #6
Bytesniffer
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Location: Long island ny
Posts: 59
Unclenick
Very technical info on
The water capacity. This explains
Clearly why the volume is
Larger for my case.
If I subtract the space for the
Boat tail bullet I'm using
Its about right on.

Also mobuck,
I definitely start low to be safe and work
Up. Previous was 39.5 grains and I had
No signs of pressure issues when examining
The case and primer after firing
20 rounds.
I think after 40 gr I'm going to go up
I'm 0.3 gr
I just want To find best combination for
Accuracy.
Case the same , bullet the same , setting
Depth same. (Cartridge overall length) same, jump the same and same powder etc

I may be crazy but I seem to enjoy
Reloading as much as shooting
No that I'm retired.
l will need to reload a lot of rounds
To break even, on what it cost to
Get to this point but , I'm not
Doing It to save money.
I'm on a quest to build reliable and
Consistent ammo that should
Translate into better accuracy.
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