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Old January 10, 2005, 02:57 PM   #1
Cowled_Wolfe
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Why are super-low charges so harmful?

Hello, I've got yet another 'how stuff does what it does' question.

Recently, I was browsing around online looking at subsonic loads on centerfire rifle cartridges. A few of the sites I visited said that too low of a load might damage your rifle. For some reason, this just doesn't make sense to me.

Big bang = ok, little bang = bad?

What would make a rifle's action fail under a low pressure but hold against a larger pressure? Are certain kinds of actions more prone to problems? Why is it ok to do a super-wimpy load in a .22 rimfire, but a risk in a full bored centerfire?

TIA for any insights,
Wolfe.

I don't reload, so don't worry about me blowing myself up btw...
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Old January 10, 2005, 03:03 PM   #2
OBIWAN
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Well...if the round does not exit the barrel there is reason for concern

Other than that I Got Nuthin!
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Old January 10, 2005, 03:26 PM   #3
Bill Z
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I'll see you on the barrel clearing and raise you bouncing back off the target and putting an eye out!

I dunno, I'm stumped on that one too. I know we pick on pistol shooters a lot that do powder puff loads and some of the are sensitive and get their feeling hurt, but other than that and not enough powder to clear the barrel and running one behind it is all I can see.
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Old January 10, 2005, 03:32 PM   #4
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Wolfe, it doesn't make sense to me either, but believe it.

The problem is very light charges of slow burning powders. I remember reading an explanation of the danger of explosion when firing ammo loaded with very low quantities of fast powder, but I don't remember exatly how/why they go BOOM. But that is the danger.

Light charges of fast burning powders are the way to go for safe ultra-light loads. They are not dangerous, although you will eventually stick a bullet in your gun barrel.

As for stuck bullets. They, in themselves, are not at all dangerous. What can be dangerous is shooting another bullet while you have a stuck one in the barrel. The gun can come apart throwing shrapnel-like pieces injuring you and/or bystanders. That is a very different danger than light loads of fast powder, and it is much easier (for me) to understand.

Hopefully, someone with a good understanding of the light charge of slow powder problem can explain it to all of us.

.
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Old January 10, 2005, 04:02 PM   #5
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Could be, when a slow powder is lightly loaded, all the powder can lay parallel to the axis of the case, making it's entire surface available for ignition? More surface area = higher pressure.
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Old January 10, 2005, 04:39 PM   #6
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I think the Lee manual explains it a bit although in a bit of a biased way basically saying it's a myth. My guess without looking is that since the powder quantity is so low, it all gets burned up in the shell case at once instead of being spread out over travel time through the action and barrel. Just a guess.

Randy
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Old January 10, 2005, 04:42 PM   #7
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The problem is that light charges with very slow burning powders. This has been known for many years and was proven in the laboratory. Under these conditions the powder can "detonate" instead of burning and create extremely high pressures and blow up the gun. This is why you see the statement in the books with slow powder ' do not load less than 10% below max' or similar statement. Reduced loads of slow powders are not efficient anyway so just use a faster powder.
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Old January 10, 2005, 06:11 PM   #8
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mete's right. Small charges of slow powders can cause what is known as "secondary explosion effect" or SEE. Charles Petty wrote an excellent article on the SEE in Handloader several years ago. After reading it, I realized that I had experienced it one time with a slow powder in a 22-250. I talked to him about it (on a BB) and he agreed that it had happened given the load and effects I described to him. I don't want it to happen again - trust me. Fortunately, it happened with an extremely strong rifle, a Rem 788, which is built like a bank vault.

I'll see if I can locate the article for reference.

.
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Found it. The article is titled "Mystery Solved!" and is in the June-July 1997 issue of Handloader. Very interesting read.

C_W asked, "What would make a rifle's action fail under a low pressure?" It won't. To summarize SEE, the problem with small loads of slow powder is that the powder is ignited, the pressure drops below the critical threshold to keep it going, then the remainder of the powder ignites - all at once. You have a detonation instead of a controlled burn. The pressure will spike far above SAAMI limits before the bullet is very far along the bore.
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Old January 10, 2005, 07:02 PM   #9
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Thankyou for such a complete response, Mal... It's scary to think a low load can flash to a higher pressure than a bigger one.
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Old January 10, 2005, 07:12 PM   #10
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Hey folks,

I would tend to believe the whole slow burning powder pressure excursion this is a reloading community myth. There has been many articles written about how it happened somewhere according to someone third or fourth hand, but I have never seen any scientific duplication of the effect published by any competent laboratory.

Several years ago, I personally spoke with Mssrs. Tom Brown and Mike Dailey of the Hodgden Powder Company, and they said their laboratory examined the reports of slow burning powder pressure excursions, but they have never been able to duplicate any such pressure excursions in their lab.

I heard about such pressure excursions when I first started reloading over forty years ago, and it continues to be told today -- in spite any empirical evidence of same. When I first started reloading back then, I used the very slow burning 4831 powder for many different loadings, and that included squib loads too. My squib loads were squib loads and never "detonated."

Best widhes,
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Old January 10, 2005, 08:26 PM   #11
Mal H
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Nope, David, not a myth. You have to read the cited article. Petty used a universal receiver and pressure testing equipment. They experienced pressures ranging from around 49K up to 82K using the same load of slow powder. IOW, he does have scientific data to support the theories. (The test barrel/receiver was in 6.5x55 Swedish.)

One thing I didn't mention is their finding that the most likely cause of the apparent explosion is a stuck bullet. As the bullet leaves the case and enters the leade, pressure drops below the necessary level and the bullet stops. As the powder continues to burn, the bullet may or may not start back up. They found that leade and bore condition were huge factors in whether the phenomenon even occurred. Other factors that most likely contribute are case, chamber condition and the bullet type itself.
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Old January 11, 2005, 12:08 AM   #12
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I remember reading an article years back in one of the rags about a condition dubbed "detonation." They had pictures of revolvers with chunks of cylinder and top strap blown off. The way they described, as I remember, was that the powder could be laying in the bottom half of the case, below the flash hole. The primer flashes across the top of the powder, igniting more of it at once than would be the case if the primer touched off the back and the powder burned forward. Given the right powder, right (or wrong) quantity, air space in the case, and perhaps planetary alignment, you could get a major k'boom. I can't remember the magazine, so it'll have to remain heresay.
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Old January 11, 2005, 12:24 PM   #13
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Hey folks,

No disrespect intended to Mal H or anyone else, but citing a gun writer's article that was published in a gun magazine is not what I would consider scientific evidence. As I stated previously, Hodgdon Powder Company has investigated the stories of "pressure excursios" from the use of light loads of slow burning powder, and they have never been able to duplicate any of the reported stories.

Austin Mike cites "an article years back" about "detonation." What he describes about pistols coming apart actually sounds a lot more like accidental double or triple charges of fast burning powders in a load. Such accidental loadings can easily cause the finest pistols or rifles to come apart as described, and it can easily be duplicated in a laboratory.

Even Austin Mike states he cannot remember the magazine and that "it'll have to remain heresay." That is the problem of the myth -- no one can furnishe first hand experience, but they have heard from someone who knew someone related to someone who saw it happen.

The whole concept of the scientific process demands that a theory be examined and duplicated by independent sources before any hypothesis be accepted as accurate scientific truth. When such examinations have been accomplished, the findings would then be published in appropriate trade journals -- not in a monthlygun magazine. In the case of slow burning powder pressure excursions, this has not been done by any reputable scientific laboratories to the best of my knowledge. If there are any reputable findings published, please post where such journal article could be found and read for critical examination.

It does not matter how many times undocumented stories that are told and passed along. Until it is documented, it is like Austin Mike said, hearsay. Myth is also a good term.

Best wishes,
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Old January 11, 2005, 12:54 PM   #14
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You're right I'm sure, David. The light load of IMR 4831 (60 gr bullet) I used when playing around with loads that caused a very hard extraction, an extremely flat primer and a web increase of .0015" is a myth. The 82,000+ pressure spike CEP observed with a load that shouldn't have approached anywhere near that is a myth. I'll see if he can have the Lawrence Berkeley Lab redo the experiments and publish in Nature.

Yes, I'm being a little sarcastic (ok, a lot sarcastic ). But I feel you're ignoring some good data from one of the most reputable "gun writers" in the industry. I do wonder how much testing Hodgdon really performed specific to the phenomenon and how much of that testing, if it was performed, was done with IMR (mine was DuPont) powders. Sometimes the statements from company representatives are even more suspect than statements from reputable gun writers. Both sets of statements can and should be taken with a grain or two of salt.
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Old January 11, 2005, 02:12 PM   #15
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I have no idea who talked to who at hodgdon, but I have bought their annual Magazine with reloading data. The last was 2002, The article by Rick Jameson starting on page 8 talks about picking powders, and narrowing down the best powders, In summary, he states powders for rifles, that fill 85% of case capacity after seating the bullet, to stop the chance of velocity variations from propellent position. On the next column over, he states With powders in big cases it is particulary important to make certain you have a case full of powder. The point is to never reduce a charge of slow-burning powder below a manual's listed starting load. If you are looking for a reduced-velocity load and reduced-recoil loads they list some with easily ignited H4895 powder for many popular rifle cartridges. It sounds like this could be a bad thing, I believe it, I will scan the page in. Lyman has a lot of loading for lead bullets at reduced velocities. This is page 11, the last 2 columns state what people are saying, about it being dangerous, it does not mention explosions or anything it just mentions not to do it. I have my opinion on why it happens, but that is not the point I believe it happens, and there are safer ways to get certain results, than to deviate from a bullet manufacture, or powder manufactures recommendations. At least think about the people who may be around you. The revelant portions are the last 2 columns. Hope this helps. If the quality of the scan is bad, I can post each column separately.
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Old January 11, 2005, 02:15 PM   #16
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Sounds like fodder for an episode of "Myth Busters" on the Discovery Channel, don't it?
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Old January 11, 2005, 02:17 PM   #17
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It looks like the scan is not very good, can it be read, or should I scan in each colum, and post it, or is there another way to get the info out?
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Old January 11, 2005, 03:20 PM   #18
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Here's what I know (not much)...I loaded some 30/06 with a starting load and got backed out primers. The way it was explained to me is that not enough pressure to give the oomph that holds it back against the breech, allowing the primers to back out slightly. In worser case I was told that it can blow primers, or give you gas blow by by the case not expanding to grip the walls of the chamber.

Thats what I know, heresay but plausible, no scientists involved. I've heard the detonation stories...Carved in stone fact or not, there seems to be enough to this phenomenon to make a guy be careful with light loads.
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Old January 12, 2005, 10:57 AM   #19
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Worth repeating from Hodgdon:

Quote:
............... The point is to never reduce a charge of slow-burning powder below a manual's listed starting load. .......
My Hodgdon #25 gives NO wiggle room for slow burning H110 in the 44 mag rifle section and Mr Winchester warns to use it's cousin (W296) "..exactly as shown.." and "...do not reduce..." (along with mag primers and heavy crimp). Neither powder manufacturer lists any H110/296 loads for lower pressure rounds like the 44 Spec or 44-40.

Why go there when faster powders are available for safe reduced loads?
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Old January 13, 2005, 12:26 AM   #20
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On a different note light charge fast powder note -

I'm sure many of you will remember the NRA publishing in their magazines work that disparaged the double/triple charge notion with light charges of Bullseye. Their work said it had to be bullets lodging because the charges were so light a double charge mostly wouldn't blow at all and certainly nowhere near the observed damage.

Personally I suspect the detonation deflagration transition is real and I'd not be surprised to learn powder behaves something like a hot wood fire where instead of being slow to light at all the wood is suddenly burning everywhere at once - or maybe the powder is heat distilled into some explosive component - but since I know flour or grain dust will explode I'm not going to assume it can't happen with gun powder.

I am sort of surprised there isn't more on it in the limited market technical literature. I'd think a German expert would have written a 13 volume treatise on it but no such luck.
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Old January 13, 2005, 05:55 AM   #21
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Low power rounds can be very dangerious

One of the main problems is that the powder in the case will not cover the flash hole for the primer. If the gun was pointed down the powder would fall to the front if the case leaving the primer hole open. Then when fired the flame of the primer flashes over the top of the powder and the pressure can get really weard. I.E. one round can fire normaly the next can stick in the barrel or worse, sound like it diddnt go off and you have unburt powder in the barrel and a bullet. There is no better way to blow up a gun than this.
The best is to have a case totaly full of powder, to do that ammo manufacures had the secrets to add fillers so that this cant happen.
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Old January 13, 2005, 06:26 AM   #22
John Y Cannuck
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I did some work with H110, trying to come up with a load for the 44-40. Hogdon refused to give me one. I soon found out why.
To do this sort of stuff, you have to be somewhat insane, and have a lot of experience handloading. Both of these, I sadly fit into.
Anyways, after considerable sweat, and calculating, I came up with my estimation of what would be the max load for an 1892 Winchester, with the bullet I was using. I then backed off a tad, and ran it through the chronograph.
(After a remote safety firing of course). The results were scary. Velocities were all over the map, variations of 200 fps were common. I increased the powder load, and the variations smoothed out. This did not happen, until I was pushing the pressure limits of my gun. The idea has been discarded as unsafe.

oh yes, don't bother asking for the loads the answer is NO.
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Old January 13, 2005, 09:32 AM   #23
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This business about H110 is not the same thing as small charges of slow powder in bottle neck rifle cases. I have personal knowledge of a mil surp that blew up with a small charge of slow powder. Stuff happens.

I also have personal knowledge of reduced H4895 (youth) loads as published by Hodgdon. They work. But then again 4895 is not really a slow powder like 4831 or others further down the burn rate list.

For anyone who wants to be a disbeliever, fine. I was going to say why don't you try a bunch of really light slow powder loads and report back, but then that would make me liable, so I won't recommend it. As a matter of fact, don't. There are other ways to get where you want to be. sundog
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Old January 14, 2005, 10:03 PM   #24
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My point was that there may be more than one cause for these detonations, or whatever they may be. The example of H110, was just to show the evidence of what may be going on.
H110, works best at or near max. Other powders may also have their quirks.
For reduced loads in a variety of cartridges, I use Bullseye, it has yet to give me a problem. Outside of being a bit dirty. Of course the danger of a double charge is always present with reduced loads. Always check your powder levels. A double charge of Bullseye, could be a real surprize.
There are lots of theories as to why these kabooms happen, and those that believe, and don't. I'm a believer myself, and outside of my idiot experiments, I tend to err on the side of caution.
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Old January 15, 2005, 12:17 AM   #25
drinks
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Detonation

I have been reading about this "detonation" business for more than 50 years, I have never seen any reputable testing lab reports of this actually happening, I do not accept anything put out by a magazine writer, they are primarly interested in increasing circulation, not , verifiable and repeatable results.
Mostly just hysteria, I will believe it when some reputable lab can demonstrate it on demand, so far as I know, this has never happened.
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