Issue With Corbon DPX Ammo

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Mad Chemist

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So I was inspecting my carry ammo today after a range visit and to my surprise some of the rounds were visibly shorter than others. I pulled out the calipers and measured a COAL ranging from 1.082-1.115. The scary part was that I was able to shorten the COAL by squeezing a round between my fingers. I shrunk it down to 1.075:what:.

I emptied all this stuff out of my mags and replaced it with my 124gr XTP handloads for now. At least I know they will pass the push test.

I sent the following to Corbon via their website just know. I'll post up their response when I receive it. I hope they are responsive.




Hi,

I carry Corbon DPX 95gr ammo in 9mm. I recently inspected my loaded magazines and found multiple rounds with significant bullet set-back. About half of the rounds measured between 1.10-1.14" for cartridge overall length. A few of my rounds measured less than 1.10, with the shortest measuring 1.082. I unloaded and set aside all of the rounds that measure less than 1.10".

I was able to seat a bullet deeper into the case simply by squeezing it between my thumb and forefinger. It reduced from 1.090 down to 1.075 where it stopped. I noticed that the case cannelure is not as aggressive on this batch of DPX ammo when I compared it side by side with my .380 DPX ammo and my 9mm Powerball ammo. I am not able to squeeze any of my powerball bullets deeper into their cases nor am I able to do this with any of my other factory ammunition except the 9mm DPX.

I have a few questions:
Is this ammo safe to fire? I have serious concerns about the amount of setback and the fact that there does not seem to be adequate case neck tension to prevent further set back. I should not be able press the bullets deeper with my fingers.
What is the minimum safe overall length for this cartridge loading?
How short can this OAL get before a dangerous pressure situation will occur?
What is the factory spec OAL for this cartridge?

I have the original box, the UPC code is 7 57750 09980 7

Thanks your help,
Jason Hight
 
Just a suggestion they may need the lot numbers on the box also...whatever you do don't shoot any of it...with the bullets that loose the pressure will not build up when fired...you don't want anything like a squib load to happen
 
Thats some EXPENSIVE ammo to have a problem like that. I only use HST and Ranger for SD ammo. I like Corbon DPX but I cannot pay almost $2 a round. I always shoot a mag before relying on any carry ammo so Corbon gets expensive quick. Hope they do you right!
 
...with the bullets that loose the pressure will not build up when fired...you don't want anything like a squib load to happen
Click to expand...
No it won't.
Quite the opposite in fact.

The deep seated bullets will increase pressure, perhaps to a dangerous level.

But probably not.

In any case, you should Never be able to deep seat a bullet just by squeezing it with your hand.

Corbon got some splainin' to do.

rc
 
And as usual RC is right.
Compressed load = higher P.


I know exactly how dangerous this ammo could potentially be. I intentionally used a questioning tone and asked rhetorical questions because I want prompt service and I don't want to come off as a know it all to Cor Bon's customer svc reps.

To their credit, one of Cor Bon's customer svc reps sent me an email the following day requesting my contact info. She told me they intend to send me a shipping label. They want to replace the ammo and they want to inspect the defective stuff.

I expected that they would replace it without much hassle. I am pleased that they seem to show a genuine interest in investigating this defect.

I am waiting for the label and further instructions. I'll update the thread as things progress.

Oh BTW, the manufacture date is 2011. If you are running DPX from around this date in your guns, it may be prudent to inspect for bullet setback.
 
Seems like I recall Remington having this problem with their Mega packs of 9mm UMC ammo a while back. They requested return and replaced. I recall pics people posted with some rounds WAY shorter than others. I had a box at the time, but all was well with mine.

Russellc
 
I still haven't received a shipping label or any further communication from Cor bon. I sent a follow up email yesterday with no reply. I will try calling them on Monday and hopefully they will be more responsive.
 
Actually, I'm not at all surprised.

It's these type incidents and other serious one's that inspired me to start reloading in the first place over 30 yrs. ago.

In addition, I stopped carrying factory ammo for the same reason several decades ago, I now only carry my reloads for SD.

Regarding pressures and set back RC nailed it spot on. The only thing I wanted to add is that, if any cartridge is potentially dangerous do to pressure sensitivity due to set back, it would be the high pressure 9mm. As stated in my old Speer #10, bullet set back of .030" in 9mm more than doubled pressures, 28,000 cup to an astounding 62,000 cup.

GS
 
I didn't see it mentioned, but do you chamber a round and un-chamber it everyday? Bullet setback is common when people constantly load the cartridge day after day. Ramming it up the feed ramp repeatedly will loosen the round and cause set back. If you're doing this and always using the same few rounds, there's your issue.
 
Speedster,

I do unload my carry ammo a lot because I shoot my carry gun a lot. I know that frequent chamberings can lead to bullet setback, that is exactly why I was inspecting the ammo in the first place.

Chambering would explain some bullet setback but it does not explain why I could seat the bullets deeper with my fingers. The problem is a lack of case neck tension and a worthless case cannelure.
 
Sure I can see that. I have a coworker that carries the hornady FTX stuff and after a month or so of everyday chambering's, he had significant set back and you could move the bullet with your finger. When that happens he just gives them to me and I rebuild the round.

Alan
 
I whipped up a fresh batch of carry ammo last night.

124gr XTP
VV3N37 6.5gr--This is the current published max from VV but I have tested up to 7.1gr in both my 9mm pistols.
COAL 1.142"

I used new starline brass and I chamfered the cases. This allowed me to use hardly any belling on the case mouths. The seated bullets weren't budging at all when i pressed them against my bench. I threw my whole body weight into it and they still wouldn't budge:).

I've proven this load before with the same powder lot. Just for safety's sake I whipped up a test batch with some sorted used brass that I save for testing. I'll shoot them up today and assess how controllable recoil is from my Shield. If I can keep them grouped "minute of fist" under controlled rapid fire I will probably just standardize this as my carry ammo.
 
Set back is simply the bullet being seated deeper by the gun. It's caused by multiple collisions of the bullet with the feed ramp. It is not as common as people make it out to be. Good ammo with sufficient case neck tension should be able to withstand many chamberings without exhibiting any set back.

Bullet set back will not cause the bullet to be able to be seated deeper with minimal finger pressure. The root cause of this problem is inadequate case neck tension. The set back is just a symptom of the problem.


Speedster,

How are you rebuilding you friend's ammo? If the bullets are coming loose in the case (which is a different problem than the one I am having with the DPX) there is a problem with bad neck tension and too much crimp. I hope you're not running this stuff over a Lee FCD.
 
Regarding pressures and set back RC nailed it spot on. The only thing I wanted to add is that, if any cartridge is potentially dangerous do to pressure sensitivity due to set back, it would be the high pressure 9mm. As stated in my old Speer #10, bullet set back of .030" in 9mm more than doubled pressures, 28,000 cup to an astounding 62,000 cup.
Click to expand...

I totally agree Gamestalker. I think my #11 Speer has that same warning.
I was also concerned that the increased friction and greater bearing surface of the all copper bullet in the DPX might compound the issue.

I wish Barnes would publish more data their pistol bullets. The powders they list are limited and none of them are currently residing on my bench.
 
In post # 14 you touched on something that relates to how I've been seating all jacketed pistol bullets for the last couple decades.

Ever since the inception of the .40 cal., and because my dedicated 10mm dies would not reach the case mouth to bell or crimp .40 brass, I tried just chamfering the case mouths, no bell or crimp what so ever. Since that day I have not belled or crimped a single pistol case, and have not had a single issue with set back, even with repeated chambering of the same cartridge.

GS
 
I shamelessly stole that idea from you:evil:

I does make seating a little more difficult and it takes a lot longer. I'm going to keep doing this as a extra QC step for SD or hunting ammo. I'll stick with conventional belling for practice ammo.
 
No it won't.
Quite the opposite in fact.

The deep seated bullets will increase pressure, perhaps to a dangerous level.
Click to expand...

Well I disagree with you.... if the bullet is that loose where you can squeeze it between you finger as the OP stated ......the gas pressure will not build up properly and pressure will not be as high as a properly crimped round. Now I will agree that setback causes over pressure when the bullet is crimped properly or is substantially tighter than the OP stated that's a given. Either way I would still not shoot them.
 
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Sorry pal, you are wrong.

The pressure builds so quickly in the small volume of the case that the overpressure state will occur as the bullet just begins to move. The round will exit the bbl with higher than intended V due to overly high P. Whether or not it damages the gun or shooter will depend on how high that pressure gets. The defect I described will not lead to a squib. The ammo is definitely suspect and potentially dangerous, but the danger will not be from a squib load.
 
^^^^ this. Poor neck tension in a pistol cartridge is not going to cause a low pressure situation if set back happens, pressures are still going to spike as Mad C. stated.

GS
 
Whenever one opens a new box of ammo intended for carry in an auto pistol it's prudent to:

1. Do a really firm push/press test on a good sampling of the rounds, measuring before and after for setback.

2. Chamber a few rounds a few times, measuring before and after for setback.

If there are failures, reject the box.

In my experience, failures are really rare. But they do happen as Mad Chemist has shared. Prudence, therefore, is the word of the day.
 
I'm not a bench shooter, but I will hazard a guess that if light neck tension caused an appreciable loss of pressure, then the practice of initially seating bullets "too long" with light tension and then finally "seating" them to fit the rifle chamber by having the lands push the bullet back into the case when chambered wouldn't have lasted very long. Especially if it resulted in a squib. Even benchresters seem have little patience with loading practices that result in squibs. ;) From what I have read, pressure builds so fast that case neck expansion releases the bullet long before it has cleared the neck.* But, all I know is what I read. ymmv

*Let me rephrase that: Not only because pressure builds so fast, but also because it takes so little pressure to expand the neck enough to release the bullet.
 
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