why specific bullet weights?


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Sven
January 5, 2003, 03:37 AM
is there rhyme or reason to the selection of the various 'standard' bullet weights?

For example, in 9mm did early loaders discover that weights of 115gr, 124gr. and 147gr. had some particular ballistic stability versus other weights, or were these arbitrary decisions?

thanks!

-s

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Blackhawk
January 5, 2003, 03:43 AM
Arbitrary within a range of weights.

115gr bullets at a particular peak pressure give certain ballistic characteristics, but very few 115gr bullets weigh exactly that. A shooter accustomed to 115gr bullets through his 9mm might not be happy with heavier, slower 147gr bullets, so he's liable to buy only cartridges with 115gr bullets.

Sort of like buying clothes of a particular size. Individual ones vary, but you get close to a standardized fit.

P95Carry
January 5, 2003, 03:45 AM
Never ''arbitrary'' IMO .... but as ever ... a trade off... the 9mm x 19 luger case is so short on capacity, plus being a high pressure round ....... that the practical spread of bullet weights is sorta ''pre-determined''.

After that it's the old ''slower and heavier ---- lighter and faster'' debate!

I stick with 125 grainers for my cast handloads ... always seems a good compromize.

Mike Irwin
January 5, 2003, 03:47 AM
Good question!

In some cases, I know the bullet weights came about due to changes in design.

For example, when .38 caliber rounds like the .38 Long Colt were changed from a heeled bullet to the kind of bullet we now have today, weight dropped.

In other cases I'd say that the bullet weight was at least in part determined by the physical characteristics of the gun.

Blackhawk
January 5, 2003, 03:49 AM
If you can prime a case, add the powder, then choose a bullet weight between 115-147 grains, I call that arbitrary. But you do get different ballistic characteristics depending on the bullet weight.

Maybe arbitrary isn't the right word, but it'll probably do since any other word of similar meaning would be arbitrary.... :D

WonderNine
January 5, 2003, 04:33 AM
Well, from what I understand the luger was designed to shoot 124gr. I typically stick to that for my ammo selection. It seems to be the best functioning weight and has speed and accuracy of the lighter bullets without the drop of the heavier ones, but the penetration power of the larger weights (147gr.).

I almost always carry 124gr. NATO, but I also tend to carry 127gr. Winchester Ranger SXT +P+ in mid-Summer and when I know things won't get wet.

chaim
January 5, 2003, 04:38 AM
At least half of us seem to be answering "why did you pick the bullet weight you usually go with" but it seems to me that sven is asking why the particular weights were standardized (why 115, 124 and 147gr as opposed to 120, 130 and 150 or 113 and any other random numbers within the possible range for the caliber). If that is the case, I really don't know but I would be interested in the answer myself.

New_comer
January 5, 2003, 05:39 AM
That "undefined" trend of odd 'grainage' also goes for all the other calibers as well.

Pretty interesting to know why... :confused:

Matt G
January 5, 2003, 05:49 AM
There's several reasons why they come up with those weights. Usually, it's a function of the caliber and the ideal bullet shape for the application. Consider the ideal shape for a rifle bullet. If you are to keep the weight down to up the velocity, and still wish to have the best ballistic coefficient available, there's a very finite amount of mass that you can put into a bullet.

As I understand it, the common varminter weight of 87grains for .257 bullets came from efforts to come up with a factory load for the .250-3000 that would break 3000 fps --no small feat in those days! They just backed down from 100g until they got to a weight that would consistantly break 3k fps.

Hal
January 5, 2003, 09:27 AM
:D
So, at 7000 grains per pound, how may kilograms is a 124 gr 9mm slug anyhow?

Seriously, all of what's been mentioned and then some. As I understand it, most calibers/weights decend from the original muzzle loading standards, based on number of rounds per pound of lead. The requirements of the particular arms, and the refinements of the ammunition and components have altered standards over the years. Political pressures, govenrment requirements have also influenced a number of things also. Matter of fact, the above mentioned 9mm Luger itself was a victim of government intervention. George Luger was all set up and the tooling was all in place to begin production of the .30 cal Luger when the spec was changed calling for a larger caliber. If he would have used beefier components to begin with, who knows,,,the 10mm/.40 S&W family might be celebrating it's 100 year anniversay pretty soon. As it was, a 9mm caliber was the largest he could squeeze out of the P08 without changing the entire setup.

Hkmp5sd
January 5, 2003, 09:32 AM
I think they resulted from a bunch of guys with pocket protectors and slide rules. Taking the diameter, velocity, material, density, shape and probably a whole bunch of other factors, they determined the optimum bullet weight for a given caliber and application.

sensop
January 5, 2003, 09:40 AM
The caliber (diameter of the bullet) is the biggest factor in determining the range of useable bullet weights for a given chambering. Next come barrel length and powder capacity. After that it probably does come down to your choice of flat trajectory (velocity) vs terminal energy.

Chamber (case) shape and the ratio of case capacity to bore volume (expansion ratio) is part of the recipe too. But the limits are usually determined by the diameter of the bore. There is an upper and lower limit to the length of a bullet, based on its diameter, for stability. Those "size" limits determine the weight limits. Of course, how much copper vs lead is used in the mfr of the bullet is a factor too.

Imagine a .308 bullet that weighs 500 grains. How long would that sucker be? Off the top of my head, over 2 inches long. You'd either have to extend the throat waaaaay out into what would be the rifling (bore) of a normal SAAMI chambering or you'd have to sacrifice some powder capacity by seating the bullet way back into the case. The latter can really cause severe problems. Even if you managed to overcome these two problems in this example, you'd have to deal with the added bearing surface of the longer bullet. All other things remaining the same, pressure goes up.

Extremely short (i.e., light weight) bullets can present their own problems. Some component mfr made (probably still does) a 110 gr half-jacket "plinker" bullet in .308. The little sucker had quite a jump from the case neck to the point of sealing the bore when cooked off. The result was a notable sacrifice in accuracy. Also, going to faster powders to get the velocity of the light weight bullet up can get dicey in a bottle-neck rifle case.

Published reloads are based on ( I should probably say, "are intended to never exceed") a pressure limit that is established for the SAAMI chamber and bore (land/groove) dimensions.

cratz2
January 5, 2003, 11:15 AM
My pure guess is when given cartridge is designed, the developer(s) does his research and comes up with what he thinks is the ideal weight. On down the road, other folks come up with different weights as an alternative or for different uses. With 9mm, I believe 124 Gr was the original weight and it was developed with the idea of lighter/faster principle. On down the road, others decided to either go with an even lighter/faster weight and developed the 115 Gr. Someone wanted a little more penetration capability and came up with the 147 Gr.

Another possibility is that maybe one weight was determined and then the ammo companies came up with different weight alternatives to sell more ammo.

I think this woud only apply to cartridges developed before about 1960 or so. After that, it seems that many cartridges were developed with versatility and more weights available right from the start.

Boy... that was pretty long-winded and didn't really answer the question. :p

waterdog
January 5, 2003, 01:48 PM
I do believe the 115 was developed for HP applications, and the 147 gr for subsonic.

waterdog

Keith
January 5, 2003, 01:57 PM
I think you guys are missing the point of the question. I think he wants to know why the SPECIFIC weights - why 147 grain instead of 150, or 124 instead of 125.

I think the answer to that is that when designing a bullet mould/manufacturing technique for the first time you can't really calculate the exact weight because of jacket thickness and other factors.

If you're shooting for a 150 grain bullet (for added pentration) and after you run the first batch they turn out to weigh 147 grains, you aren't going to start over. You just designate that weight as the standard and others copying the design do likewise.

Keith

Shawn Dodson
January 5, 2003, 02:02 PM
Probably has more to do with sectional density than anything else. If you compare sectional densities of popular bullet weights in various handgun calibers you'll notice that they're pretty much the same:

9mm 115gr & .45 ACP 185gr share a common sectional density of .130.

.40 S&W 155gr, .38/.357 125gr, .45 ACP 200gr, and 9mm 124gr share similar sectional denities ranging from .138 - .141, respectively.

.40 S&W 180gr, .45 ACP 230gr, .38/.357 145gr and 9mm 147gr share similar sectional densities ranging from .161 - .167, respectively.

M1911Owner
January 5, 2003, 02:23 PM
The bullet weights are metric. 115 gr = 7.5 grams; 124 gr = 8 grams; 147 gr = 9.5 grams; 155 gr = 10 grams.

P95Carry
January 5, 2003, 03:45 PM
Hadn't bothered to look at that M1911 . very good point and interesting correlation. Mind you, that leaves my 158 swc 38/357 bullet out in the cold!!:)

Sven
January 5, 2003, 09:53 PM
M1911Owner said:

The bullet weights are metric. 115 gr = 7.5 grams; 124 gr = 8 grams; 147 gr = 9.5 grams; 155 gr = 10 grams.

That's it! I knew there had to be a simple explaination to the sequence.

Now... lets do the real conversion: conversions website (http://www.export911.com/convert/convert.htm)


115.74 gr = 7.5 grams
123.46 gr = 8.0 grams
131.18 gr = 8.5 grams
138.89 gr = 9.0 grams
146.61 gr = 9.5 grams
154.32 gr = 10.0 grams

Interesting:

1) values aren't exactly those grain weights (ie, 115 grain would really be 116 grain)

2) I wonder if people have tested the other 'quanta'... maybe 139 grains would be good for defensive ammo, etc...

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