Why Do They Only Make These Bullets This Way?


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Treo
April 29, 2008, 02:53 PM
I put this in general guns because the question deals strictly W/ the ammunition & I have both pistols & carbines chambered in .40 S&W

I wasn't really sure how to phrase the thread title but here's the question.

Why is it that I can only find .40 S&W FMJs ( I'm not talking about JHPs or others SD loads) in a semi-wad cutter ( I think that's the correct term) bullet?

I am using the word "bullet" on purpose because I notice regardless of who manufactures the ammunition.

Is there some weird ballistic reason for this?

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NG VI
April 29, 2008, 03:18 PM
I know what you're talking about, I think it's called a truncated cone, and I am guessing it has something to do with the geometry of the round, how it needs to be kept 9mm length yet be nice and heavy at the same time.

My guess.

Claude Clay
April 29, 2008, 03:22 PM
yup, thats right.....just because

not much bigger than a 9mm
not much smaller than a 45acp
but i have never, in all my years of shooting it and reloading it, mistaken it for anything else.

there probably is a real reason--perhaps feeding, energy transfer, BC or?? but as it is...it works well

rbernie
April 29, 2008, 03:25 PM
Why is it that I can only find .40 S&W FMJs ( I'm not talking about JHPs or others SD loads) in a semi-wad cutter ( I think that's the correct term) bullet?
Flat metaplats are more effective in punching holes and staying on course after impact than hard round nose bullets.

Round nose FMJ may be traditional, but it's not as effective in terminal ballistics as is a flat nose bullet.

-v-
April 29, 2008, 03:37 PM
That has been my understanding of the TC design of .40 rounds as well. The TC has better wounding characteristics then conical or round-nose bullets, similar to how all the hard-cast hunting loads that I have seen tend to be SWC/TC type. Although I'll throw out there that if you need to use FMJ for self defense, things are already going pretty poorly.

k_dawg
April 29, 2008, 03:39 PM
The .40 S&W has a design spec for "overal all length" of 1.135" with up to a 200grain bullet. This is actually shorter than the 9mm Parabellum at 1.169", which can be loaded up to 147 grains.

So, the .40S&W generally has a heavier bullet, in a slightly shorter package. The way they do this, is not having as "thin" of an oval side shape, with a trunkaged cone. The maximum use of volume would be a cylinder for a bullet shape, but the slight bevel makes loading in semi-automatics far more reliable.

Basically, the goal of the .40S&W was to achieve a higher performance, heavier load.. but still fit in the 'grip size' of the traditional 9mm, and smaller than the traditional .45acp

I.e. it was a design costraint.

CountGlockula
April 29, 2008, 03:52 PM
Good question. It solidifies my favorite caliber.

JesseL
April 29, 2008, 04:02 PM
Having a truncated cone profile as the only available profile for FMJ bullets in 40S&W also means that virtually all .40S&W rounds, HP or FMJ, have almost identical profiles. This should reduce issues of feedramp and throat geometries being tuned to only feed some bullets reliably.

RockyMtnTactical
April 29, 2008, 04:06 PM
Having a truncated cone profile as the only available profile for FMJ bullets in 40S&W also means that virtually all .40S&W rounds, HP or FMJ, have almost identical profiles. This should reduce issues of feedramp and throat geometries being tuned to only feed some bullets reliably.

That was my understanding as well.

Regen
April 29, 2008, 04:42 PM
The .40 S&W has a design spec for "overal all length" of 1.135" with up to a 200grain bullet. This is actually shorter than the 9mm Parabellum at 1.169", which can be loaded up to 147 grains.
If the 9mm Parabellum is 1.169" (or 29.6926mm), how come it is sometimes referred to as 9x19mm? Where does the 19mm come from?

chris in va
April 29, 2008, 04:53 PM
Case length.

rodregier
April 29, 2008, 06:41 PM
Actually, 1.169" is maximum overall cartridge length for 9mmx19.

sqlbullet
April 29, 2008, 06:44 PM
The modern truncated cone design is a derivative of the Keith SWC. The meplat of this design is believed by some to give better permanent wound channels than a round nose design. It also provides a better sectional density by being more volume efficient.

The Keith design was changed as the sharp shoulder of the Keith would not always feed reliably in a magazine based weapon. This design was initially used by Norma in the 200gr 10mm auto loads, and has been the standard of .400 full metal jacket ammunition since.

Other shapes can be used, although you may not be able to reach desired weights with other designs. I personally am currently using 155gr lead round nose for my practice loads in 10mm. They were inexpensive and have fed reliably in two different 10mm guns.

The 19 in 9X19 refers to the case length (.754") not the cartridge overall length. In most auto-loading handgun cartridges the case length determines headspace and is therefore quite important. If it deviates no adjustment in other components will offset the impact to function. If it is short, then the case will stretch excessively to fill the chamber and may result in a head separation. If it is long, the throat of the chamber may wedge the bullet into the case, resulting in excessive pressures before the bullet is released. In bolt action rifles this can especially be a problem as the bolt provides significant leverage when chambering a round.

Cartridge overall length is not critical in the same way to function of the weapon, although it's impact on pressure is crucial. COL can be reduced as long as powder charges are reduced as well. This is indicated in reloading manuals which will specify different COL for different loads.

The maximum COL should not be exceeded in auto-loading pistols as they will likely not fit in the magazine or feed reliably. Additionally, the force of the bullet engaging the rifling of the barrel when chambered could cause set-back which will raise the pressure when fired, potentially to dangerous levels.

The Lone Haranguer
April 29, 2008, 06:55 PM
FWIW, I've also seen .40 FMJ bullets with rounded sides (ogive), but still always with a flat nose.

rodregier
April 29, 2008, 06:59 PM
Actually, auto-loading handgun cartridges tend to headspace on the extractor, so somewhat short cases aren't that big an issue. They're held by the extractor against the breech-face.

Zedicus
April 29, 2008, 07:06 PM
Here's a Pic of the 3 diffrent types of .40 S&W I have on hand atm.

Along with Comments on how they shoot with my Glock 22.
All are 180 Grain FMJ.

http://img186.imageshack.us/img186/543/40swed3.jpg

Also Note, the Crossfire Reload on the Left also has noticeably less recoil. (why, I don't know)

LTB15J
April 29, 2008, 07:16 PM
ive seen two types of WWB. the middle one in that picture, and another that is more straight on the sides; exactly like the UMC pictured.






http://shadow.slipgate.org:8080/Weapons/DSC04873.JPG


traditional style on the left, new style on the right

jrfoxx
April 29, 2008, 11:26 PM
Flat metaplats are more effective in punching holes and staying on course after impact than hard round nose bullets.

Interesting. never thought of that. I have kinda wondered the same as the OP, since the vast majority of fmj rounds I usually see are usually rounded, or spitzer "pointy" type, but have seen some on occasion like he mentioned. never knew wh ythey were they way they were....

Pretty sure I have some bullets I picked up for realoding for my .44 mag that are like the middle one in Zedicus' pic. if the "flat" acts like the quote above, I'll have to guess it's VERY effective in something hotter like .44mag.:D
I'll have to keep that in mind whenever I go to load those specific one up, to try and take extra advantage of this fact, and mark them for more advantageous use than just plinking rounds.....

Snapping Twig
April 30, 2008, 02:54 AM
TC is a high performance hunting bullet. When I bought my Casull I purchased a 260g GC mould and it was a TC, this directly from Casull.

I liked it so much that I bought a Lee mould for my .45acp - a 230g TC. It shoots like a laser and with the large metplat it should make a fine round to use in the field on a hog hunt.

I imagine it boosts the effectiveness of the .40 a great deal. Come to think of it, I can't recall seeing a HP for the .40, they must make them too.

freakshow10mm
April 30, 2008, 03:29 AM
The TC design in a .40 S&W is a carry over from the 10mm, which was designed around a 200gr jacketd TC at 1200fps. The .40 S&W was designed around a 180gr TC bullet, which got changed to a JHP for duty, at 950-980fps.

The TC design cuts cleaner holes in paper, feeds better from a ramp, and produces a better would cavity than a round nose FMJ.

1911Tuner
April 30, 2008, 09:07 AM
Flat metaplats are more effective in punching holes and staying on course after impact than hard round nose bullets.

Correct. Testing by the US Air Force also revealed that truncated cone bullets are a bit more accurate than a RN bullet of identical weight...and they penetrate a little deeper in soft mediums at a given muzzle velocity. They also hold their velocity better over a given distance. Good bullets. I like'em.

.cheese.
April 30, 2008, 09:13 AM
Zedicus - WWB or Rem UMC have never seemed to be all that inaccurate out of my G22. They're just not match grade ammo.

I had always wondered this question about .40 SW (my favorite HG caliber too). I eventually gave up on thinking about it and just accepted it. I'm glad somebody brought it up.

spwenger
April 30, 2008, 09:23 AM
Early autoloading pistols functioned more reliably with bullets with rounder profiles. The .40 S&W is a relatively late design, born at a time when pistols were designed to handle hollowpoint bullets, with fairly wide cavities, often in a truncated-cone profile. For the reasons mentioned above, regarding various advantages to the truncated-cone profile, there really was no need for a round-nose FMJ when the .40 S&W was introduced.

Deanimator
April 30, 2008, 09:24 AM
That's a truncated cone. Semi-wadcutters have a shoulder behind the ogive (nose) that cuts a clean hole in paper. I use wadcutters and semi-wadcutters exclusively for reloading, since all of my practice is on NRA 50' bullseye targets. Scoring is MUCH easier.

Truncated cone bullets create more tissue damage when shooting people and animals, since they crush their way through, rather than parting the flesh.

sqlbullet
April 30, 2008, 10:49 AM
Actually, auto-loading handgun cartridges tend to headspace on the extractor, so somewhat short cases aren't that big an issue. They're held by the extractor against the breech-face.

This is a function of gun design, not cartridge design. The cartridge design specifies headspace from case mouth. Guns that were designed to headspace on the rim with the 40S&W are almost all (if not all) derivative of the Peters-Stahl and feature a dual extractor system. Most firearms are designed to headspace from the case mouth, and the extractor may or may not hold the cartridge securely.

If the weapon does not hold the cartridge firmly enough, bad things may happen. In worst cases the case is pushed by the firing pin past the extractor until it properly headspaces against the case mouth (as per cartridge design spec). Once the case stops, the primer will be crushed, if the firing pin has enough travel (most do). Upon firing the cartridge will be stretched and pushed back to the breech face rapidly. Pictures (http://www.thegunzone.com/10v40.html) I have seen of 40S&W ammo fired in a Smith 1076 are impressively distorted. Imprints on the case head are almost ironed out, primers are flattened and distorted, case rims have chunks missing from them.

There is an additional (and less supported by fact) concern about the effect of copper or lead fouling on the shoulder of the chamber that may occur in these cases. It is hypothesized that the build up could then create a dangerous bullet pinch at the end of the chamber when a cartridge of proper length is chambered. This is not substantiated that I know of by testing, but is suspected in some incidents involving 10mm Auto chambers and alternating 40S&W and 10mm ammo.

Sorry to deviate so far from the intended post, but in the interest of safety I wanted to clarify the issue of headspace least anyone think they can safely shoot 40S&W in a 10mm pistol.

sqlbullet
April 30, 2008, 10:52 AM
Also, back on the subject, and perhaps being nit-picky, the term is méplat (http://www.answers.com/topic/m-plat?cat=technology), not metaplat.

1911Tuner
April 30, 2008, 11:02 AM
Actually, auto-loading handgun cartridges tend to headspace on the extractor, so

Actually...no they don't. Not unless there's somethin' bad wrong with your pistol.

JesseL
April 30, 2008, 11:16 AM
Early autoloading pistols functioned more reliably with bullets with rounder profiles. The .40 S&W is a relatively late design, born at a time when pistols were designed to handle hollowpoint bullets, with fairly wide cavities, often in a truncated-cone profile. For the reasons mentioned above, regarding various advantages to the truncated-cone profile, there really was no need for a round-nose FMJ when the .40 S&W was introduced.

I remember one or the other of us (not sure which now) saying that same thing when this question came up on the old packing.org forum.

Zoogster
April 30, 2008, 11:57 PM
As mentioned a truncated cone creates a better wound and keeps the round straighter after impact.
When a bullet impacts an angled surface the first part of the bullet to hit causes the round to begin to tumblein that direction. if that is a flat edge like on a truncated cone, it will only tumble for a split second until the other side slams into the target and then resume a more relatively straight direction.
A rounded bullet however gets turned sideways and goes more off course after impact.

At the same time a truncated cone has a lower ballistic coeffecient because it is less aerodynamic. So it will bleed energy faster at distance than a rounded nose bullet the same weight and velocity.


Wounding is increased with sharp edges. Tissue flows around a projectile, and if it can do so over a smooth surface the wound channel will close back up smaller than the actual round.
A projectile with sharp edges disrupts that tissue flow, and even tissue flowing around it gets cut or pushed forward along those edges.
For that reason a shape with multiple sharp edges like a cube or star would be even more devastating at close range for a given weight and velocity against soft tissue. It would however have horrible accuracy due to awful airflow and an awful BC meaning it would bleed energy rapidly over distance, plus barrels are cylindrical and have spiraling rifling.

So a truncated cone has some of the benefits of an irregular shape while still being practical in use.

Treo
May 1, 2008, 12:01 AM
Thanks guys I appreciate the answers

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