Interesting observation on HP ammo

[-v-]

So I was casually browsing brassfetcher.com to see if there was some info on a 200gr JHP in the .40 variety, and noted something interesting with nearly all the high expansion JHP ammo. Once it impacts, past the first 5-8" it seems that our modern .50"+ expansion JHP ammo proceeds to turn on its side and frisbee the rest of the way through the medium. This was seen with about half of the loads in the 9mm-.45ACP range. Heavier rounds tended to stay nose-forward a greater percent of the time, additionally rounds that experienced less expansion stay nose-forward for an extended period of time. This does retroactively make sense as once the bullet enters a liquid media, like Jello or a BG, it becomes subject to hydrodynamic drag which will reorient a bullet so that it has smallest frontal area possible. The leading perpetrator in this problem seems to be the speer GD series, which seem to have a near universal tendency to turn on its side after the initial ~6". Likewise, they also tend to be the best expanders. On the other spectrum are Hornady XTP series of bullets, which while their expansion tend to not be very impressive, they do tend to remain nose-forward in about 2/3rd of the cases, much more then what Gold Dot HP's can claim.

Equally, an other interesting observation is that some bullets after expansion assume a roughly spherical profile, which seems to negate any effect of rotational forces on wound channel effects. Since the round is nearly spherical, it produces the same sized hole no matter if its going nose forward, sideways, or backwards.

The implication? Expansion, while important, might actually compromise the efficiency of JHP ammo. Instead of getting a .50"+ hole through and through the target you instead get a funnel that starts at .60"+ inches, and narrows down to a size below the actual unexpanded bullet diameter.

Some other observations: Bullet expansion characteristics can be classified into roughly 4 categories based on final bullet shape:

Cylindrical - bullets that expand to form an enlarged cylinder and proceed in a strait nose-forward direction. The front:side ratio tends to favor the front ( < 1) Many of the .38spl rounds tend to do this, and as well as 147gr 9mm JHPs.

Spherical - bullets that form a roughly symmetrical shape with the frontal:side ratio nearly identical (~1) due to the petals of the JHP folding over the base of the bullet forming a sort of ball or square. Direction of travel for this end-shape seems irrelevant. .40 180gr bullets and 230gr .45 ACP bullets tend to fall within this category

Discoid- bullet flattens out so that front:side ratio is greater on the side then the front (> 1). these bullets tend to rotate on their side, and continue to penetrate side-ways for the majority of the wound-track. Gold Dot bullets seem to love this end configuration, and it could be said that this is their distinguishing characteristic.

Explosive - bullet exhibits heavy-extreme fragmentation and disintegrates upon impact. Jacket separation is a staple, and fragments are found throughout the wound channel, or the periphery. Penetration and expansion both tend to be limited. This seems most common to the light .40 S&W bullets, of 165gr and lower, with it appearing to be endemic to the 135gr species. The expansion characteristic may be deceptive, as the entire bullet may fragment into shards producing an effect similar to the MagSafe line of ammo without using the resin-bead bullet approach (and not costing $2 a shot either!).

Feel free to add any thoughts or personal observations!

 

[FieroCDSP]

A 135gr 40 cal is humming along around 1100-1200fps, same as a fairly stout 9mm. I can see where it would more commonly fragment.

 

[NG VI]

135 .40 at 1200 is weak. Most SD 155 grain is going 1200 FPS, I looked at some federal Personal Protection 135 grain ammo, but as it was rated about 35 FPS slower than the 155 Ranger non-T I already had in 50 round boxes, I passed on that one.

 

[James T Thomas]

V ery Interesting

Your observations are interesting.

I have posted here on THR; somewhere a similar concept from such obsevations. Sorry, I can't remember the subject or title for a search.

That is that the "cylindrical" projectiles; that is those whose "aspect ratio," as you describe as length to diameter upon expansion have maintained some of the feeble sectional density property that a pistol bullet can have. -"Miniball."

The larger calibers such as 40 and 45, upon "expanding" become somewhat spherical as you state, and the S.D. of a sphere is far less than that of the cylindrical shape.

And so it is too for the "mushroom" shapes of greatly expanded bullets that become what could be described as a "coin." No S.D. at that point.

The result does not seem to be caliber dependent so much as the specific bullet weight and the degree of expansion that consumes or transforms the bullet; terminal ballistics.

I have always sought "controlled expansion" rifle ammo, and look for some semblance of it with pistol ammo. May be Hornady XTP. Though I do not rely on it for the handgun.

 

[-v-]

Well, the "coin" or "disc" projectiles might actually manage to recoup some sectional density by turning on their side, however this may have a negative impact on actual wound channel formation, as at that point they leave a wide and narrow channel rather then a tubular channel. This mechanism may be a bit of a gamble as far as wounding and stopping goes, as now you have a rather wide but narrow plane that's doing damage. With this wide plane, wounding efficiency would be highly dependent on the rotational orientation of the "discoid/coin" projectile. Essentially it turns into a self-propelled knife, rather then a spear-point as is the case with FMJ/Cylindrical . Thus, rather then dealing uniform damage, its creating a ribbon of damage through whatever.

I am rather intrigued with the "explosive" type of bullets. The effect of severe fragmentation on terminal ballistics appears quite interesting, in that you get a "shotgun" approach with the potential to inflict a lot of delocalized damage. The iffy part with it all, is that they seem to top out at 10" of penetration, 2" shy of FBI's minimum 12" and 6-8" shy of the ideal 16-18" (or was it 14-16"?) penetration. One potential "trick" that brassfetcher also advertised, and had some preliminary Jello to support was delaying the HP expansion. link In his case he used a drop or of super-glue to retard expansion. This approach added about 2" of penetration. A similar approach may work with the 135gr light loads to also delay expansion and disintigration of the bullet so that once it does fragment, the fragments are able to achieve at least 12" of penetration.

 

[James T Thomas]

afterthoughts

Please review Brassfetcher again and make another observation.

That is, after expansion occurs, how much more travel remains in the round?
What proportion is the travel length after expansion to the length before?

It appears that for expansion to occur that a significant amount of kinetic energy is consumed, and that knowing that the velocity is thereby decreased, then the remaining K.E. would be greatly reduced. -The K.E. being dependent on the squaring of the velocity that is.

I would think therefore the edgewise "coin" projectile, or fragment / shards would drift to a stop without much more travel.

This would give a whole new consideration to the bullets that open up upon shallow penetration. The "explosive" type of action.

How do you view it?

 

[Tropical Buzz]

You touch on an interesting point that many seem to miss - the expanding bullet itself is consuming a lot of the kinetic energy that would otherwise result in further penetration. The tradeoff is very debatable, but IMO a longer but slightly (like .006" or so) smaller channel has at least a roughly equivalent volume and surface area PLUS the added benefit of reaching and punching through the vitals. The whole energy dump thing is a big myth as normal handgun bullets simply do not carry enough mass and velocity to seriously shock a 180+lb assailant.

 

[-v-]

Tropical Buzz: Completley agree with your sentiments. The other thing that catches my attention is that the body is not of a homogeneous density, thus its a reasonable extrapolation that as a bullet that has a higher retained sectional density passes from one media into another, it is more likely to stay on a direct course, and less likely to be deflected by the angles between different densities (organs) within the body.

James: This is going to is a tough one to do, as its hard to glean all the information present within the gel due to only limited experience and understanding of gel results. My first assumption is that permanent cavity formation does not begin until the bullet begins to expand. My next assumption is that the bullet reaches full expansion at the maxima of the permanent cavity.

Going by these assumptions, it seems that for the first ~1" or so (it is hard to say precisely without having the block physically present to measure) the bullet is not expanding. Only after an initial entry period does the bullet open up and begin creating a permanent cavity. By permanent cavity, I am assuming that the the area outlined in red in this picture Link and the corresponding 'cavitation' within other gels correspond to the permanent cavity. Beyond this point, I can't really draw any more conclusions because there is not enough data on bullet velocity to say accurately whats going on. My intuition tells me that past maximal permanent cavity, as the bullet slows down, the channel becomes progressively smaller and and smaller, until the wound channel becomes only as large as physical bullet diameter. However, this is all pure conjecture on my part, and I have only the most passing confidence in this, as there's simply not enough data to draw any sort of conclusion.

As far as the 135gr "explosive" expansion rounds, the gel block has been photographed at an inopportune angle, making it difficult to conclude anything other then the general "explosive" type expansion has occurred. Further, with 5 bullets having impacted the same block, it is difficult to separate apart which fragments and channels correspond to each bullet, especially with 2 of the bullets having been reported to have exited the side of the block at ~10". Link to Brassfetcher's 135 Corbon .40 S&W shot

 

[McCall911]

it seems that for the first ~1" or so (it is hard to say precisely without having the block physically present to measure) the bullet is not expanding.

I think that's what some call the "jam depth" which is usually about 2 calibers in depth, sometimes more or less.