loob groove capacity

[Bloodman14]

Guys, is there any way to calculate the capacity, in volume, of a loob groove for the purpose of calculating how much loob is necessary for a given gun?

The reason I ask is this; I was looking at Tom's (Accurate Molds) list of designs, and was wanting a particular design with a larger-than-shown loob groove to be sure I had enough loob. This led me to my question; how can I determine if a boolit has enough loob?

Fully realizing that there is no 'right' answer, does anybody with a strong math background have any ideas, or anyone with lots of practical experience have any suggestions?

The boolit in question is his 31-200L, his idea of the 314299. I am also looking at the 31-200R.

[45 2.1]

Figure the area of the lube groove (use inches for all measurements)... whether it is a trapezoid [(base + top)/2 x height] or circular(harder to tell as it's not what you think it is)..... then the mid groove point of the lube groove to the centerline of the boolit (that distance x 2 x 3.142). Multiply both together and that is the capacity in cubic inches. This is a basic crude method, but close enough for what you want.

[Tom Myers]

Guys, is there any way to calculate the capacity, in volume, of a loob groove for the purpose of calculating how much loob is necessary for a given gun?

The reason I ask is this; I was looking at Tom's (Accurate Molds) list of designs, and was wanting a particular design with a larger-than-shown loob groove to be sure I had enough loob. This led me to my question; how can I determine if a boolit has enough loob?

Fully realizing that there is no 'right' answer, does anybody with a strong math background have any ideas, or anyone with lots of practical experience have any suggestions?

The boolit in question is his 31-200L, his idea of the 314299. I am also looking at the 31-200R.

Gunnerd,

If the groove is a typical rectangular profile, the process is fairly straight forward. Elliptical grooves require toroidal math to calculate.

For a typical groove with sloping sides do it like this.

First:
Calculate the total volume of the lube groove section using this formula:
GV = the volume of one grease groove
Let H = the length or height of the groove.
let D = the diameter of the bullet.
Let R = the radius or 1/2 the diameter of the bullet.
Let V = the total Volume of the lube groove section.
Lei Pi = 3.141593
Then
R = D / 2.
and
V = Pi x R x R x H. Now you have a value for the total volume of the lube groove section.

Next, find the volume of the short cylinder formed by the bottom portion of the lube groove.
So Let:
V2 = volume of lube groove bottom portion.
d = the diameter of the bottom of the lube groove,
r = 1/2 of d - the radius of the bottom of the lube groove
L = the height or Length of the bottom of the lube groove.
Then:
V2 = Pi x r x r x L. Now you have a value for the volume of the bottom of the lube groove section.

Each sloping side of the groove may be considered a truncated cone (The geometric term for the truncated cone is referred to as a frustum)
The formula for the volume of a frustum is:
Let R = the large radius or base radius of the truncated cone (The same value as above)
let d = the small diameter of the cone (this will be the diameter of the bottom of the grease groove)
let r = the small radius or 1/2 the diameter of the grease groove bottom.
let h = the height of one of the truncated cones. h = (H - L) / 2
let v = the volume of one of the truncated cones.
Then
v = Pi x h x ( R x R + R x r + r x r ) / 3. Now you have the volume of one of the truncated cone groove sides

Finally, subtract the 2 cone volumes and the bottom groove cylinder from the total groove volume.

GV = V - V2 - v - v. The volume of one grease groove.

You now have the value in cubic inches of the volume of one lube groove.
Most lubes have a Specific Gravity of 0.8851 grams per cubic centimeters. (1 cubic centimeter of water weighs 1 gram)
So the groove volume measured in cubic inches first needs to be converted to cubic centimeters by multiplying by 2.54 x 2.54 x 2.54 (16.387064)
CC = GV x 16.387064 = volume in cubic centimeters.
So using the average Specific Gravity of most lubes, find the grams of lube in one lube groove
Grams of lube in the groove = CC x 0.8851.
Now there are 16.43236 grains in a gram. So to find the grains of lube in the groove, multiply the grams x 16.43236.

Let's use the sketch below and the values to find the volume and weight of lube of the bullet.
V = Pi x R x R x H
D = 0.357
R = 0.357 / 2 = 0.1785
H = 0.11
V = 3.141593 x 0.1785 x 0.1785 x 0.11 = 0.01101080 cubic inches.

V2 = Pi x r x r x L
d = 0.32
r = 0.32 / 2 = 0.16
L = 0.08
V2 = 3.141593 x 0.16 x 0.16 x 0.08 = 0.006434 cubic inches

v = Pi x h x ( R x R + R x r + r x r ) / 3
h = (0.11 - 0.08) / 2 = 0.015
R = 0.357 / 2 = 0.1785
r = 0.320 / 2 = 0.160
v = 3.141593 x 0.015 x ( 0.1785 x 0.1785 + 0.1785 x 0.16 + 0.16 x 0.16) / 3
v = 0.001351234 cubic inches

GV = V - V2 - v - v. The volume of one grease groove.
GV = 0.01101080 - 0.006434 - 0.001351234 - 0.001351234 = 0.001874332 cubic inches
0.112996 x 16.387064 = 0.03071479 cubic centimeters

Grease Groove volume is 0.03071497 cc

0.03071479 of water would weigh 0.03071379 Grams
there are 16.43236 grains in a gram so the groove volume would be equal to
0.3071379 x 16.43236 = 0.504717 grains of water could be contained in the lube groove volume
The specific gravity of the lube is 0.8851 so
0.504714 x 0.8854 = 0.4467 grains of lube per lube groove

I realize that this is long and complex but it IS ACCURATE. about the only questionable variable would be the specific gravity of the lube, but that would probably be small enough to be insignificant.

Hope this helps

[tomme boy]

Tom you made my head hurt! I haven't done any lengthy math since getting out of college for electronics about 10 years ago. You made me have nightmares of taking test with no notes.

[tomme boy]

What are you going to shoot this in? If it is going to be in a Mosin or a Enfield, I would not overlook 31-205H and have Tom adjust the sizes for your throat.

I made the 31-215B for my Mosin and I have used it in a 303 Brit and they both shoot really well.

[Tom Myers]

Tom you made my head hurt! I haven't done any lengthy math since getting out of college for electronics about 10 years ago. You made me have nightmares of taking test with no notes.

Yeah, it does require concentration and attention but the OP did ask how to calculate the lube groove volume and that is the way it is done.

I don't particularly care for lengthy complicated calculations either. Too much opportunity for silly math mistakes that return grossly wrong answers.

That is the principal reason that way back when, I started programming the bullet drawing software that eventually evolved into the Precision Cast Bullet Design and Evaluation package that uses a computer to perform all those tedious calculations and get it right the first time

[runfiverun]

I think they said use Pi. times r squared.

I find it easier to modify the lube to carry more or less oil.
you can calculate lube volume all day.
but you cannot calculate the rate it will give up oil to the barrel or at what rate the wax will go into flow.
you can calculate it, but it will change 2000 times in a year, and probably 3 times in a day's shooting.

[Bloodman14]

Mr. Myers, your faith in my math abilities is appreciated, but may be misplaced, as I only got a 'C' in college Algebra! However, that is what I was looking for (I think!). My OP was a request to determine how much loob would be necessary for a particular application, knowing that there is no 'right' answer. I am using a slightly stiffer form of Ben's Red. The rifle in question is a No. 4 MkII Enfield, factory fresh 5-groove that is at nominal factory specs, I have only put 200+/- rounds through it, and most of those were cast.

That 31-215B looks good.

[bhn22]

Plus, different lubes have different characteristics. You can calculate volume as much as you like, but it won't correlate to lube efficiency.

[Walter Laich]

as an example Lee makes a .45 200=gr RNFP that I use in my SASS shooting--love the bullet as does my firearms.

The lube groove I this bullet seems to be tiny when compared to others but never have suffered leading. Don't push them at high speeds, though.

[MikeS]

Tom, have you ever considered making a Mac compatible version of your software products?

[Tom Myers]

Tom, have you ever considered making a Mac compatible version of your software products?

MikeS,

Yes, I have considered gearing up for Macs but there just has not been enough interest shown to justify the time, expense, equipment and workload required. The reality is that your question concerning Mac compliant software is one of approximately 25 over the last 13 years that I have received.

I am not a Mac user but I understand that reliable, reasonably priced software is readily available that will allow one to run Window's applications on Mac machines.

The issue that most concerns me is that more and more software users are demanding applications for I-Pads, I-Phones and other hand held equipment. Miniaturizing and condensing the Precision Software content into meaningful, useful applications is going to require a daunting amount of re-education and innovation to be successful.