Disigning.308 wichester for long range (better than warner tool company if the math are correct)

T

The Spirit

New member
Hello people, How are you?

I'm Chilean and I live here, and I have plans to go US for a long time in the future.

Well, here we have.308win or may be 6.5creedmor, nothing more in rifle ammo. I prefer .308, because barrels long last more, much more. Change barrel in chile it's a pain in the arse, you can do it, but you have to pay the shipping+ taxes + another taxes for inspection and give explanations to authorities why you need a new barrel and that has to match with what you say, for example, my barrel has wear out as a reason, the army it's going to take your rifle and to inspect the throat of the barrel, if you lie, you are ****** up(it is said that you enter in a banned list, like something "hey this is suspicious, this guy told us to bring a barrel here and the reason was fake, Why he did that?, put this guy in the radar", but it is a rumor, there is no proof about that in years), if it's true, you have green light.

So, I plan to purchase a rifle in the future, in 308, but i don't like the BC of the 308 that's in the market, so, I'm designing bullets to get something better. That's why I'm doing this, because I like design things and for exposed reasons above.


I did the first calculations, and i get a bullet of 159.3 gr a G7 0.452 BC at 2.5 mach=2791.125 FPS, twist rate of 9.8, COAL MAGAZINE 2.9" (maximum size that i have found for magazine SR25 pattern, that's the condition)

As a second attempt, i saw that the center of gravity was near to nose and i reduced the length of the nose and i got 158.4 gr, a BC of .4495 in G7, at 2.5 mach=2791.125 FPS, twist rate of 9.8, COAL MAGAZINE 2.9"(maximum size that i have found for magazine SR25 pattern, that's the condition)



i used only cooper at 59F, 1 atmosphere, and 50% humidity, which mean a density of copper of 8,962151176 grams/cubic centimeters
I don't know if the bullets can be patented or something, but It doesn't match me why nobody does the bullets of warner tool apart of them, because they are the best in the market. So, if this is true, well, I don't want to keep this in secret i would patent this as a free content.

So, i want to give you the dimensions of the bullets but I don't know if someone can stole my work and patent it. I would like to reveal here the measurements to get a feedback.

other thing, how much length of the bullet goes inside the brass to measure the volume available for powder?
 
Perhaps I am not much fun, but for myself, I will rely on Nosler or Sierra or Berger or Hornady or Barnes or Lapua,etc.

I do not say that to discourage you, i just think that for myself, have good reason to evaluate my skills and resources. (And remain humble!)

Here in USA, its not so hard to buy excellent bullets.

I do like cast bullets for revolvers. Those I can do.
 
The Spirit,

Welcome to the forum.

I don't know your design parameters, but the first G7 numbers you gave are so high for a 30-caliber bullet that I'm expecting a lot of sectional density was involved, obtained mostly by length. This would mean a very fast twist would be required to achieve stability. If you use the approximation that a stability factor of 1.5 is close to ideal, have you run the designs through any of the online calculators to estimate that? A couple of different approaches are here and at this site.

the calculation of case space is based on what is called Case Water Overflow Capacity. this is the volume of water the case will hold when its primer pocket is plugged and it is filled with water that is level with the case mouth (no meniscus). It is determined by weighing the empty case and then the filling as described, making sure to tap it a little to avoid trapping bubbles, and making sure there are no water droplets on the outside. You then weigh the filled case and subtract the dry weight from the result. What you get is Case Water Overflow Capacity in grains of water weight. Divide by 15.43236 to convert to cubic centimeters (CCs) unless you measured in grams, in which case you have the CCs because they equal the number of grams. If the water is at room temperature, divide the result by 0.997 to adjust for the expansion of the water above 4°C (the temperature at which water is most dense). Once you have that number, you can calculate the volume of the seated part of your bullet and subtract it from the Case Water Overflow Capacity. The resulting value is called Case Water Capacity (without the word "Overflow") and is the term used to describe how much room you have for powder under the bullet.

The CAse Water Overflow Capacity of 308 Winchester cases varies by the manufacturer from about 55 grains (3.56 CC) of water to about 59 grains (38.2 CC) of water, with 57 grains (3.69 CC) being a common number.
 
Unclenick said:
The Spirit,

Welcome to the forum.

I don't know your design parameters, but the first G7 numbers you gave are so high for a 30-caliber bullet that I'm expecting a lot of sectional density was involved, obtained mostly by length. This would mean a very fast twist would be required to achieve stability. If you use the approximation that a stability factor of 1.5 is close to ideal, have you run the designs through any of the online calculators to estimate that? A couple of different approaches are here and at this site.

the calculation of case space is based on what is called Case Water Overflow Capacity. this is the volume of water the case will hold when its primer pocket is plugged and it is filled with water that is level with the case mouth (no meniscus). It is determined by weighing the empty case and then the filling as described, making sure to tap it a little to avoid trapping bubbles, and making sure there are no water droplets on the outside. You then weigh the filled case and subtract the dry weight from the result. What you get is Case Water Overflow Capacity in grains of water weight. Divide by 15.43236 to convert to cubic centimeters (CCs) unless you measured in grams, in which case you have the CCs because they equal the number of grams. If the water is at room temperature, divide the result by 0.997 to adjust for the expansion of the water above 4°C (the temperature at which water is most dense). Once you have that number, you can calculate the volume of the seated part of your bullet and subtract it from the Case Water Overflow Capacity. The resulting value is called Case Water Capacity (without the word "Overflow") and is the term used to describe how much room you have for powder under the bullet.

The CAse Water Overflow Capacity of 308 Winchester cases varies by the manufacturer from about 55 grains (3.56 CC) of water to about 59 grains (38.2 CC) of water, with 57 grains (3.69 CC) being a common number.
Click to expand...
Hello Nick
i fixed the bullet to fit in 2.9, i guess. But i still have the original one
Bullet Weight: 153.6 gr
Twist 10.4 at 2.5 mach
BC in G7 0.435 G1: 0.870


Well i have been using that calcs i use the geoffrey first then the jbm. Look at this link:

http://www.geoffrey-kolbe.com/cgi-b...adius=17.747&weight=153.6&density=8.962151176


https://jbmballistics.com/cgi-bin/jbmdrag-5.1.cgi with this numbers and results
 

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I'm not aware 6.5 creedmoor wears out barrel particularly faster than .308 win. My load with 145gr bullet has MV of 2600fps, which is only slightly faster than .308 win with 150gr bullet going at 2590fps. But I guess it is possible if I go with a hotter load of 2700fps.

Barrels mostly wear in the throat. Instead of replacing the barrel, is setting back an old barrel any easier in Chile? Some work on a lathe to move the breach face and the shoulder, and the chamber reamed deeper to remove the eroded throat.

An old timer shooting 22-250 told me his trick to keep his barrel life long. Slow down and let the barrel cools down between shots.

-TL



Sent from my SM-N960U using Tapatalk
 
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The Spirit,

I expect you got a look through the late Robert L. McCoy's book Modern Exterior Ballistics? Pages 73 and 74, in particular for the boattail angle.

I notice in your linked information the Cd has some surprisingly wild swings. I looked more closely and spotted an entry error. The error is that you shortened the boat tail to 0.0599…" but didn't change its diameter to match the effect of the shortening on the 7.5° slope. You left it as 0.2002", which is what I suppose it was with your original design. With the boat tail angle at 7.5°, If I subtract 0.2002" from 0.308", I get 0.1078". If I divide that by 2, I get the base diameter reduction for each half of the bullet profile, which is 0.0539". When I divide that by the tangent of the angle, tan(7.5°), I get a boat tail length of 0.4094…", and not 0.0599". This accounts for that impossible-looking Cd curve.

Conversely, if your intended boat tail length is 0.0599", then you multiply it by tan(7.5°) and double it and then subtract it from 0.308", you get a boat tail base diameter of 0.2922…". When you plug that in, you also get a very reasonable-looking Cd curve, but you also lose BC because drag reduction by a boat tail depends on how much smaller it is in diameter than the bullet-bearing surface.

This practical problem of a shallow boat tail angle making the boat tail impractically long was determined by trial and error by the U.S. military just after WWI to have a best compromise at about a 9° boat tail. It won't be as low in drag as the 7.5° boat tail with the same base diameter, but it will be shorter enough to make a bullet that can center in the bore without too much tilt. Such tilt moves the center of gravity of the bullet away from the bore axis, setting up a centrifugal effect that will make the bullet experience a dynamic jump at its exit from the muzzle, creating drag that stays with it all the way to the target.

Please note that this board ordinarily does not allow publishing an image from another website without the site owner's permission, but I have asked for and received that permission from Geoffrey Kolbe in the past, so it is OK to use it here. Same with JBM Calcs. However, you need to be sure to credit them, as you did with your link names. If you have questions about this, please look at the board's policy on posting copyrighted information.
 
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