A Look at Corbon .357 Magnum 125-gr. DPX Ammunition
By Stephen Camp
In 1935 the .357 Magnum was born. It was conceived after a gun writer of the period worked up energetic handloads in .38 Special using the S&W .38/44 (N-frame) revolvers. His name was Phillip Sharpe and it seems that Douglas Wesson was mightily impressed by the way it performed in the hunting field. Smith & Wesson soon built an N-frame revolver for the new cartridge.
The .357 Magnum cartridge is 0.135" longer than the parent cartridge from which it was derived. This was not so much for increased case capacity as it was to make sure that the much hotter load was not loaded into a .38 Special revolver.
.357 Magnum Specifications:
Cartridge LOA: 1.590" maximum
Case Length: 1.290"
Case Trim Length: 1.285"
Primer Size: Small Pistol
SAAMI Maximum Average Pressure: 45,000 CUP
Bullet Weight Range: Usually about 110 to 180 grains
Traditional Bullet Weight: 158 grains
The .357 was used all over the world to take all manner of large game, some of which would be considered too much for the caliber today. It gained a good reputation in the hunting field. Its effectiveness was probably exaggerated a bit, but it also worked its way into this country's police holsters and the hands of private citizens wanted what might have been called the "most powerful handgun on earth"…at least until the .44 Magnum came along about 20 years later.
We'll focus on the defense aspects of the .357 Magnum in this article and see what Corbon's new 125-gr. DPX load has to offer.
Hunting or Defense Applications?
Since this cartridge sees sporting use in the hunting arena as well as defensive duty in suburban "jungles", it might be worthwhile to briefly touch on differences between ammo intended for hunting and that engineered to deck a felon.
In the hunting field we never know exactly the shot angle that the animal might offer. We are more interested in getting into the vitals from any reasonable angle for the caliber being used and would like an exit wound to enhance bleeding. That does two things: It hastens the animal's death and allows for a better blood trail. Unless hunting dangerous game it is not essential that the animal drop in its tracks (though it is nice) so long as death is forthcoming and we can track the animal via a blood trail.
Heavy recoil is to be expected and is a secondary consideration. Fast repeat shots are not the norm with hunters. They want to make the first shot the only shot if possible but all shots are precisely aimed. Though some hunters do like expanding bullets when hunting, it is my observation that if it comes to expansion or adequate penetration, they'll choose the latter. This is why flat-nose FMJ, hard cast SWC's, and less-aggressive expanding bullet's like Hornady's XTP are popular with those seeking game with their hunting handguns. Accuracy is also of prime consideration for handgun hunters.
Examples of .357 "hunting" ammunition usually exhibit bullets from the heavier end of this cartridge's weight spectrum. Corbon offers their "Corbon Hunter" line which features .357 loads with 180 and 200 grain bullets moving at 1200 and 1150 ft/sec, respectively when fired from 4" barrels.
If these loads with heavy bullets are good for killing deer and other larger quarry, why not use them for self-defense?
When looking at defense applications of the .357 Magnum, we see that while some aspects are common between the hunter and defender, others are quite different.
How "hard" a .357 "kicks" depends on a couple of things besides the subjective observation of the shooter. One is the load being used. The other is the size and weight of the revolver being used. Revolvers initially built in this caliber were the large S&W N-frames. The Model 27 in its 3 1/2" barrel was used by FBI agents and its near double but less nicely finished Model 28 Highway Patrolman graced Texas Department of Public Safety Troopers' holsters for decades. Eventually S&W introduced the .357 Model 19 Combat Magnum. This was built on their medium size K-frame. Obviously a full-power 158-gr. SWC is going to "kick" more from the Combat Magnum than from the heavier Highway Patrolman. Eventually complaints about long-term "fragility" with the K-frames when fed heavy diets of magnums led to the slightly larger and beefed up L-frame. Examples are the popular Model 686 in various barrel lengths. I saw lots of these in police holsters until the law enforcement community began the rapid change to semiautomatics in the last half of the 1980's. Today it seems to be the exception rather than the rule to see uniformed officers toting double-action revolvers. (You can bet that some small revolvers are carried as backup guns.)
This .357 Magnum from S&W is the Model 27, has a 3.5" barrel, and is an example of their N-frame revolver size.
Here we have two examples of the S&W (K-frame) Model 19 Combat Magnums. These guns were enormously popular in police circles when I began policing in the early 1970's.
It wasn't long before the notion of lawful concealed handgun carry by private citizens began to become reality in many states…and I'm happy to say that more are being added to the list all the time. Evidently enough wanted an easily concealable .357 Magnum revolver that makers began cranking them out. What was said about recoil in the K vs. N-frame also applies in spades to the small J-frame and especially the latest super lightweight models. A .357 load that is comfortable in an N-frame might not be "bad" in an L-frame, tolerable in a K-frame, but torture in the small steel J-frame and hell on earth in the super small titanium guns.
Here we see a couple of Corbon .357 Magnum 125-gr. DPX cartridges flanked by the popular Ruger SP101 (left) and the S&W "Customs Service" version of the Model 686 (right). If the same load is fired in both revolvers, the smaller lighter SP101 will exhibit greater felt recoil than the larger heavier L-frame. The Ruger is by no means the lightest small revolver in this caliber and it can get "energetic" with some full-power magnum loads.
Such does not lend itself to either accurate shooting or fast repeat shots that might be called for in a fight for one's life. Buyers of small .357 Magnums want more power than is offered from the hotter .38 Specials but nothing is gained if the load is uncontrollable.
Where hunters are usually seeking their quarry from daylight to dusk, a self-defense scenario can unfold in dark or semi-dark conditions. Thus, muzzle flash can be a consideration in self-defense ammunition.
The hunter seeks to kill what he hunts, but unless it is a dangerous animal it isn't a life-or-death matter if it drops right where it was hit or travels a few yards before collapsing. When shooting to save our lives, we are not shooting to kill but to stop. That an unlawful aggressor might die from being shot is certainly possible, but our primary purpose in shooting him was to immediately stop his actions when no other reasonable alternative existed.
At the same time we do not want too shallow of penetration so that a "stop" cannot be had, but we also fear a bullet overpenetrating and winding up in some innocent third person's forehead. (I sometimes think this concern is more in the mind than actual threat, but there are examples of it happening.)
Based primarily on the FBI standards for acceptable bullet performance, many opine that penetration of at least 12" of ballistic gelatin is necessary to reach deeply enough within an adult male torso should that bullet pass through an intermediate target such as an arm before entering it. Some prefer 12 to 14". What we don't want is a bullet passing through a solid adult torso with enough power left to kill or injure anyone else. At the same time we want the bullet to be reliable in expanding. We want it to open as designed even if it passes through intermediate "hard" barriers like wood or glass before smacking into our adversary.
In short, we want "enough" but not "too much" and we do demand quite a lot from bullet makers.
Evolution of Defense Ammunition:
Originally when a person opted for a .357 with factory ammunition, they got the full-power 158-gr. swaged SWC. I am personally aware of two instances in which Remington 158-gr. SWC full-power .357 Magnum rounds were used, neither with the desired immediate effect. One involved an officer with another agency having to shoot a knife-wielding opponent. Though struck solidly in the torso, he required two shots before he finally quit advancing. This actually was not bad performance, but this shooting occurred in a residential area at night with most folks home. Both rounds completely penetrated the aggressor and while no innocent persons were hit, the bullets or what they might have hit were never found. The other incident involved a woman with mental problems who murdered her husband. As he slept she entered the bedroom and beginning below belt level worked her way up his torso with the same load mentioned previously. Evidently he sat up after the 5th shot passed through his torso for the sixth was found in the wall after it passed through his head via the left eye socket. This one did the trick for the psychotic wife. Though his eyelid was found stuck to the ceiling, his head was not grossly misshapen from the magnum's impact. The five bullets fired while he was supine completely penetrated his torso, mattress, box springs and were in the wood floor beneath the death bed.
In both cases the revolvers were Smith & Wesson's and both had 4" barrels. Evidently the officer's aim was better as his opponent "stopped" and died after two rounds while the deranged woman's sixth shot stopped all further movement from her husband forever.
Concerns about "stopping power" led to the use of JHP ammunition with the 125-gr. semi-jacketed hollow point from Remington or the Federal 125-gr. JHP gaining top honors amongst gun writers for years. Winchester had .357 Magnum Silvertips in both 125 and 145-grain weights. Both were popular ammunition with law enforcement. In 10% ballistic gelatin the 125-grain loads usually penetrated between 12 and 14" while the 145-gr. Silvertip penetrated a bit deeper.
The problem was that heavy clothing could sometimes clog bullets so that expansion was retarded or nil and most of the 125-grain loads fragmented. I have never seen either a full-power Remington or Federal 125-gr. JHP that failed to expand in a human being, but they do frequently fragment. For years this was considered a good thing by some but after the Miami Fiasco on April 11th, 1986, the call for deeper penetration without bullet fragmentation replaced the call for aggressive expansion.
During this time frame there was much R&D by bullet manufacturers, especially in 9mm, since "high-capacity" 9mm semiautomatics were gaining much ground among the rank and file of law enforcement. Operating in the same general velocity range and being nearly the same diameter, much of the improved 9mm's bullet technology translated easily to the .357 Magnum.
With more and more private citizens carrying more and more concealed .357 revolvers, some ammunition makers began offering the newer designs at attenuated speeds. Though not full power they still offered more "whammy" at the receiving end than did the .38 Special +P from the same barrel lengths. Remington came out with a "mid range" .357 Magnum SJHP and later with their "new technology" Golden Saber. Other companies followed suit and today we find "short barrel" loads offered more than ever before and with bullets that expand reliably over a fairly wide velocity range.
One of the latest entries is from Corbon and is designated "DPX" for "Deep Penetrating X-bullet." Let's take a close look at this ammunition and see if it might fill a niche in our own defensive revolvers.
Corbon .357 Magnum 125-gr. DPX:
The bullet is constructed of a homogeneous copper alloy and has a wide deep hollow cavity measuring approximately 0.177" wide by 0.350" deep if measured as close as possible to its cone-shaped bottom. Looking inside the hollow cavity it becomes clear that the bullet is either pre-stressed or scored so that it will exhibit six uniform "petals" when it expands. There is no jacket to possibly separate or fragment and no lead core that might break apart, depending upon what was struck.
Here is the Corbon 125-gr. 357 DPX bullet. Note the scoring or pre-stressed areas on the inside wall of the hollow cavity. This bullet is not likely to fragment. The DPX line of bullets has a good reputation for expanding reliably after passing through barriers including the now standard 4-layers-of-denim.
Corbon's .357 DPX load uses new nickel-plated Remington cases and the primers are sealed. At the right we see a disassembled cartridge. LOA measures 1.577". Bullet diameter measures 0.356" and this one weighed 125.1 grains and the powder charge, 7.8 grains. The powder is flash retardant. Nominal listed velocity from a 4" revolver barrel is 1300 ft/sec. This load is designed to penetrate at least 12" of 10% ballistic gelatin. (It is not unusual for expanding bullets other than cast or swaged to be slightly undersized for caliber. The expand to fit the bore under the pressures generated upon firing.)
I disassembled the cartridge shown above using a kinetic bullet puller; it was tough! Corbon has made sure that these bullets are most unlikely to unseat themselves during the sharp recoil impulse which common to the super light snub revolvers. Even though this is not usually a problem in steel compacts, it is reassuring to know that Corbon has engineered this ammunition to work in all .357 Magnum revolvers.
The Corbon 125-gr. DPX is shown here (above left) with a Hornady XTP. Both weigh 125-gr., but the X-bullet contains no lead. It is less dense than the jacketed XTP, which does. Note that both have very prominent crimping grooves. At the right we see the Corbon DPX flanked by two other .357 Magnum loads. The other two are both from Remington. The top one is their Golden Saber and the bottom is their full-power semi-jacketed hollow point.
Shooting:
Shooting was done for accuracy and done at distances of 15 yards & 25 yards, slow-fire using a rest. These distances should far surpass the majority of distances common to deadly force situations. I am not interested in ammunition that is not capable of greater accuracy than I can use even if I probably cannot attain what it's capable of in a stress situation. Comments concerning felt recoil will also be given, but keep in mind that such comments are always subjective.
I tried to use different size revolvers as much as possible. The smallest 357 revolver I own is a Ruger SP101 with a 3 1/16" barrel. It represents the compact 3" guns so popular these days. The shortest barreled K-frame 357 I have is an S&W Model 19 with a 2 1/2" barrel. It represents the K-frames and the snubs. Since the longest barrel usually seen used for self-protection is 4", I used my S&W Model 28 to represent that group as well as the N-frame owners.
15 yards:
Five shots were fired slow-fire at 15 yards using a rest with the 2 1/2" bbl Model 19. Recoil was quite mild and this revolver had been sighted in for Remington .357 Magnum 125-gr. Golden Sabers. I was not surprised to see that the DPX was "on" with that sight setting.
Next up was the Ruger SP101 with its 3 1/16" barrel. This was the best group of the day and is probably luck. This fixed sight revolver hits dead bang "on" with 145-gr. STHP's at this distance using a center hold on the bullseye. Like the Remington 125-gr. .357 Golden Sabers, the Corbon 125-gr. DPX hits just about a half-inch or so low at this distance…at least for me. Recoil was just a little "snappier" than from the snub K-frame with its larger size and handle.
This 4" Model 28 N-frame was like shooting a "pop gun" with the DPX rounds. This one was still sighted in for a 158-gr. handload and the 125-gr. DPX hit slightly low and left by roughly 1.5".
25 Yards:
From the 2.5" Model 19, the DPX load that had been "on" at 15 yards was approximately 2.5" high at 25 yards. If carrying this ammo in this revolver, I'd go with a dead-on hold at 15 yards and under, but six o' clock at 25 yards.
The Ruger SP101's POI didn't change that much when coupled with my human imprecision. I cannot tell if the group actually struck slightly higher or if my POA was just a bit higher. For whatever reasons, I can go dead on out to at least 25 yards and using this revolver with this ammo, a dead-on sight picture should be well within "minute of felon heart" expectations.
Some will criticize for not doing more "practical" shooting since this is self-protection ammunition. What must be remembered is that I didn't have a limitless supply of this ammo and my reasoning remains that if it will group well when shooting for precision, it will certainly be "accurate enough" for the quick and dirty drills.
I did not shoot the S&W M28 at 25 yards since its sights were off for the DPX load. There is no mystery here; I didn't want to change the sights from their current setting as that is usually but a two load gun: the 158-gr. CSWC handload and 145-gr. Winchester Silvertips. I have no doubt that the 4" revolver would group quite satisfactorily with the 125-gr. Corbon DPX.
Expansion Testing:
I do not have the money for 10% ballistic gelatin testing. Even if I did, I damned sure don't have a climate-controlled laboratory in which to test it at the constant temperature required for repeatable results. My informal expansion work was done using water and then by shooting into super-saturated newsprint. Corbon 125-gr. 357 Magnum DPX was fired from all three guns. Therefore, we can see its expansion when fired from a 2 1/2, 3 1/16, and 4" barrel. Firing was done 5' from the newsprint and 25' from the water.
Here are the results. The numbers in the left column designate barrel length while "WP" stands for "wetpack", what soaked newsprint is sometimes called. "W" simply means water. I measured across the widest points of the bullets that expanded in water and weighed them as well. None lost over 0.1 grains according to my scale. I did not weigh those fired in the wetpack since some of it is embedded in the bullet.
The DPX fired into water from the 2 1/2" Model 19 measured 0.685" across and 0.573" tall. From the Ruger, we got 0.701" wide by 0.567" tall. The 4" barrel resulted in an expanded DPX measuring 0.651" wide by 0.561" in height. As you can see, the results in wetpack are visually quite similar.
Here is a side view of the Corbon 125-gr. DPX. These bullets were fired from the Ruger. The one on the left struck super-saturated newsprint while the one on the right hit water. You can see that these bullets do not attempt to turn inside out as do some aggressive expanders and they do not fragment resulting in loss of mass. I strongly suspect that they will make quite "nice" wound channels.
I also fired a few other maker's bullets from the same revolvers to allow a visual comparison with the DPX.
Here we see different bullets fired into wetpack. The DPX bullets at the bottom of each picture were the only ones fired into water. On the left from the S&W and from top to bottom are Winchester 145-gr. STHP,
Remington 125-gr. Golden Saber, Remington 125-gr.SJHP (full power), and Corbon 125-gr. DPX. From the Ruger on the right and top to bottom are Remington 125-gr. Golden Saber, Winchester 145-gr. STHP, Remington 125-gr. SJHP (fragmented) and Corbon 125-gr. DPX. Results from the 4" barrel were virtually identical.
Chronograph Work:
The average velocities for each revolver were determined by firing 10 shots each approximately 10' from the chronograph screens.
Corbon .357 125-gr. DPX
| Revolver/Bbl " | Low (ft/sec) | High (ft/sec) | Average (ft/sec) | ES (ft/sec) | SD (ft/sec) |
| S&W M19/2 1/2 | 1110 | 1155 | 1133 | 45 | 21 |
| SP101/3.16 | 1152 | 1205 | 1176 | 54 | 24 |
| S&W M28/4 | 1167 | 1233 | 1196 | 66 | 27 |
It appears that this load is fairly consistent with regard to velocity. Increasing the barrel length by 1 1/2" only resulted in an average velocity gain of 63 ft/sec, but going from 2 1/2" to 3 1/16" resulted in an average velocity gain of only 20 ft/sec less.
This is one of the very few times that actual measured velocities did not equal or exceed Corbon's listed velocities for a load. From the Ruger and the 4" S&W we got within 100 ft/sec on the high readings, but average velocities were 124 ft/sec and 104 ft/sec less, respectively. My observations with this company's ammunition have usually been average velocities running 50 to 75 ft/sec faster than what is published. This no doubt explains why felt recoil was considerably less than expected.
Conclusion & Observations:
This new load from Corbon proved to be capable of very good accuracy and it reliably expanded. Though not picture perfect, the bullets consistently opened up and held together. As mentioned earlier, flash retardant powder is used in this ammunition and the bullet is expected to penetrate at least 12" of 10% ballistic gelatin.
No news here but it had greatest felt recoil in the SP101 with its smaller handle, much less in the Model 19, and was negligible in the 4" N-frame. If one is recoil sensitive but wants more ballistic performance than with the hot .38's, this would be a load for consideration.
There were no failures to fire and cases extracted easily from all three of the test guns. Cleaning the barrels required no more work than usual. In other words, the copper alloy X-bullet did not excessively foul the bore.
I would like to see the velocity a bit closer to the 1300 ft/sec range from a 4" barrel, but can "live" with the load as is.
All Corbon DPX ammunition is packaged in 20 round boxes. For information on pricing and other calibers available, take a look at www.corbon.com
For those interested, Corbon also offers a line of "traditional" aggressively expanding JHP's in several calibers and these do meet or exceed published velocity figures. They also offer heavy bullets in their deep penetrating, heavy bullet hunting loads as well as their unique "PowRball" line of aggressively expanding ammunition.
My carry load for the SP101 has been the Remington 125-gr. Golden Saber. This mid-range .357 load is simply easier to control than more powerful loads. It averaged 1189 ft/sec from the gun with a standard deviation about the same as the Corbon DPX. As reported earlier, the DPX from this revolver averaged 1176 ft/sec, virtually equivalent to the Golden Saber. My SP101 will be loaded with DPX once I clean it up.
We have seen several bullet designs hit the market and often be tweaked and refined into even better versions. The DPX line is new. I have no doubt that with time this already good bullet design will become even better.
