Smokeless powder detonation?

Discussion in 'Ammo & Reloading' started by pokute, Oct 13, 2014.

  1. pokute

    pokute Sincere as a $5 funeral

    1,620
    2
    0
    Hi Folks,

    If you have been reading online gun forums for long, you have undoubtedly seen mention of a phenomenon that could be called "light load detonation". Now, based on a great deal of reading of the reports of this phenomenon, the reports of guns destroyed by unknown causes, and guns destroyed by double charges, I am inclined to believe that double charges are almost always to blame.

    I can think of one other possible mechanism for failure when shooting hot handloads.

    There is a condition familiar to engineers called "constructive interference of dynamic stresses". Constructive interference in an elastic medium can cause stress to be doubled. It occurs when stress waves reflect off of each end of a structure, for example a cylinder, and return to meet at some point near the center, resulting in a peak stress nearly double (sometimes more) what is calculated for static systems.

    In all real mechanical systems there are dynamic stresses that exceed calculated static stresses. This is the reason for the seemingly arbitrary engineering safety factor of "2", which you see now is not so arbitrary.

    The usual methods of stress measurement in guns is a real dynamical measurement, and therefore all contributions to the measured stress are accounted for, the safety factor is intended to account for material defects, not for overloads or deep seating.

    That is why gun design engineers warn against EVER exceeding book load values. That said, I do it myself. I hope that if you are doing it you are taking precautions to avoid injury in the event of blown cylinders or, WORSE, a blown case in a pistol setting off a mag full of bullets in your fist. You are at the mercy of your weakest case when your chamber is not fully supporting.

    The makers of large guns and cannons perform a pre-stressing treatment called "autofrettage". They seal up the gun, muzzle and breech, and then fill it with water or oil under very great pressure to just under it's yield point. The result is that a residual compressive stress is induced that can as much as double the ultimate strength (hoop stress limit) of the gun, and can increase it's service life considerably. A similar result is NOT achieved by cryo-treatment, as is sometimes claimed.

    As with everything I write, I invite questions or disagreement. My intention is not to "take on all comers", but to educate.
     
    Last edited: Oct 14, 2014
  2. cloaker

    cloaker Lifetime Supporting Member Lifetime Supporter

    44
    0
    0
    I wonder if you had, hypothetically, a 1 foot long bullet, and you had powder loaded up to 1/4 of an inch from the seated bullet, and you fired that bullet in your imaginary gun, how much of the powder would simply blown out vs it all igniting, which I doubt it would do. Once your bullet reaches it's maximum pressure via the combustion of the powder it doesn't matter how much powder is left, its all going out the front with the bullet so perhaps hot loads reach that limit before the bullet is expelled unlike regular recommended loads who should in theory burn most of the powder to create the pressure required to move the bullet out of the brass?

    I'm speculating, you know I've been shooting for a little over a month and have not much of a clue, but I think some very basic physics are at play, with complex possibilities when small factors are changed, like loading more grains.

    Fascinating topic!

    Dave
     

  3. pokute

    pokute Sincere as a $5 funeral

    1,620
    2
    0
    It's a little more complicated because there are very different types of powder available. Without looking at the chemistry, and considering only the "speed" of the powder, a slow burning powder will not burn completely if the MINIMUM pressure required for sustained ignition is not maintained. A fast burning powder like Bullseye has a relatively low MINIMUM pressure for sustained ignition.

    Now, given that, why does loading manual data appear to show low MAXIMUM pressures for fast burning powders? Because loading them up hotter (more powder) causes the PEAK pressure, which occurs very quickly with Bullseye, to increase to an unsafe level rapidly.

    And why is a fast powder, like Bullseye, better for precision target shooting? Because it produces a relatively short impulse, and the bullet is driven forward by the expanding gas, producing a smooth, continuously decreasing acceleration. A slow powder, like 2400, generates a longer impulse that consists of an accelerating production of gas that is maintained in a compressed state, developing pressure in a way that maintains a high degree of acceleration for a relatively long time, and then may or may not reach the point where expansion of the existing gas takes over, depending upon the length of the barrel and the charge.

    So, possibly not explained at all above (because I'm trying to be brief and not exceed my own attention span), but in conclusion, a fast powder can reach a dangerous pressure faster than a slow powder, and there is (practically, within the confines of a normal gun) not a maximum pressure beyond which the powder stops burning - A double charge of fast powder will generally end in catastrophy. A slow powder may stop burning when the bullet leaves the muzzle because the MINIMUM pressure required for sustained burning has been lost (I observe this with my go-to 44 magnum target load of 12 grains of HS-6).
     
    Last edited: Oct 15, 2014
  4. cloaker

    cloaker Lifetime Supporting Member Lifetime Supporter

    44
    0
    0
    I didn't think about the different types of powder. I have a lot to learn, but one thing that is fascinating is the endless possibilities.

    I could imagine someone coming up with their perfect round using a combination of materials and amounts. This would seem to be a challenging hobby, one that I am going to undertake.

    Unlike baking, the consequences for making mistakes can be devastating, so with this in mind, is there a way to test your bullet without actually confining it inside a barrel and pulling the trigger? A bullet tester of sorts...? If not, maybe we should build one!

    Ok, I know, first, I should learn to clean the brass, something I'm working on and already had that "OH! CRAP. YEAH..." moment when I had what I've termed the pregnant round. When the 9mm brass is inside the 40 round and that is upside down in the 45 round and none of them come out clean! Ok, sort the rounds BEFORE cleaning!

    I came up with three different recipes and the end results are suspect because in every batch I had too many pregnant rounds. I have now sorted the rounds and will be redoing the experiment in the next few days and post my results.

    Does the cleanliness of the reloaded round affect the powder and its efficiency... is there a minimum standard for cleanliness for reloading?

    Dave
     
  5. pokute

    pokute Sincere as a $5 funeral

    1,620
    2
    0
    Yeah, it always amazes me how the little cases find their way into the bigger ones!

    Cleaning brass is one of those areas where you CAN do your own thing, because the actual requirements are pretty minimal. As long as the flash hole is clear and the primer seats deeply and firmly, you are good to go (of course, no oil inside the case).

    That said, I am a little silly about case cleaning. I sweeten the corncob media with a teaspoon of Maas metal polish and a teaspoon of New Finish car polish. I clean between 1 and 2 thousand cases in a single batch of media (basically, until picking the cases out of the media makes my hands black). I tumble until they are bright and shiny and fairly clean even inside. This removes a lot of brass, but doesn't seem to hurt the cases any. I reload my cases until they show incipient cracks.

    I use Lee U dies for sizing. They size slightly smaller than spec, giving improved case tension, and they also prevent problems with tightly chambered guns.

    I use Lyman M dies for expanding. I find that I can expand exactly as much as is necessary and no more with the M die. I hear Redding has silently stolen the profile of the M die and uses it in all their new dies.

    I generally use Redding seater dies. NOT the fancy ones with the micrometer. I usually use a plug that has been milled flat, since the fancy profiles never fit any of my bullets correctly. I seat the plug as far down in the die body as possible to avoid (or at least minimize) crimping while I am seating.

    Crimping can be interesting. For taper crimp nearly anything will do. Taking the plug out of a seating die and using it to crimp is usually fine. I usually get a couple of roll crimping dies for revolver calibers, and then I use the one that does the neatest job. Some of them shave the brass in a funny way when you crimp hard. Avoid those.

    Once you have dies you like, they are your friends for life.

    Of course you want to be certain that your press and dies are plumb, centered, and square.

    I use an RCBS Uniflow powder measure. Note that when you buy it, it comes with a cylinder that is WAY TOO BIG to throw pistol charges. Call RCBS and they will send you the small cylinder FOR FREE.

    Some powders have large grains and don't meter very consistently. Julian Hatcher noted in the 1930's that Unique meters badly, but shoots very consistently! I verified that this is true. I like Unique a lot in 45 acp and 44 special.

    Other powders I like a lot are Power Pistol for small cases like the 9, 40, 10, and 38 special, HS-6 for moderate loads in 44 magnum and 45 Colt, and 2400 for full magnum loads in 44 and 45 Colt.

    If you find yourself leaning toward Blue Dot, check out Power Pistol as a better behaved alternative. I only use Bullseye for loading down when shooting to less than 50m. Trying to get high velocity out of Bullseye is just wrong, so avoid finding yourself with only Bullseye on hand during the next crunch.

    I ALWAYS look inside the case before seating the bullet and verify that the powder is at the right level.

    Oh Dem cases:

    Oh the 25 fits in the 32
    and the 32 fits in the 38
    and the 38 fits in the 40
    and the 40 fits in the 44
    and the 44 fits in the 45
    and maybe somebody who shoots bigger stuff can finish the song.
     
  6. pokute

    pokute Sincere as a $5 funeral

    1,620
    2
    0
    Elmer Keith invented the "Duplex Load", where he soldered a small
    tube inside the case from the flash hole to near the base of the bullet, filled that with fast powder, and filled the rest of the case with slow powder. This worked very well, but somewhere along the line the fact that he used a little tube to hold the fast powder got forgotten, and people started blending powders, which is crazy.

    You need to develop charges in the guns you will be shooting them in. If you get the bug to do something borderline dangerous, make sure you have the best quality gun and possibly aftermarket barrel that you can buy. I have been working up some 10mm loads for the Springfield Omega that I will never be able to publish!

    Measuring pressure signs requires a clear understanding of your materials. You can't just pick out some brass and go crazy. You need to start with some factory rounds, measure the brass before and after firing very carefully, and then reload that brass and measure the effect of your load compared to the factory load, and make a determination based on your estimate of the pressure effects on the unsupported part of the case (for auto pistols), primer pocket, etc. It's much harder to work up hot loads for a revolver because there's usually no warning before things start to go wrong in subtle ways. Measuring case heads is a potentially dangerous metric unless you really understand how a case fails. Difficult extraction can be misread because of chamber roughness (though difficult extraction already means that things are going wrong and the gun may be weakened).
     
  7. cloaker

    cloaker Lifetime Supporting Member Lifetime Supporter

    44
    0
    0
    There are so many variables, it's mind boggling and obvious to me that if I don't follow the instructions exactly I would be in danger of something bad happening since I have no clue about what I am doing.

    On the good side, yesterday at the range I met a regular who everyone at the range says is the loading expert (30 years) and he's offered to help me get off the ground. His advice seems to mirror what you are saying, stick to rules, don't experiment until you actually know what you are doing, not just think you know what you are doing!

    I will be content if I can learn to reload those 45 hp and range ammo... for now
     
  8. pokute

    pokute Sincere as a $5 funeral

    1,620
    2
    0
    Those old guys at the range are a great resource. A lot better than online forums, where any fool can give advice :D My shooting partner is an old guy with vast experience who taught me bullet casting.
     
  9. cloaker

    cloaker Lifetime Supporting Member Lifetime Supporter

    44
    0
    0
    Casting, thats my plan in week two! Lol joking, maybe year 10!


    Sent from my iPhone using Springfield Forum
     
  10. pokute

    pokute Sincere as a $5 funeral

    1,620
    2
    0
    When you consider that casting brings the price of ammo down to about 15-20 cents, There's no excuse not to start. I only bother casting 44 and 45LC bullets. I run ZERO swaged in 38 and 45acp, and ZERO jacketed in 10mm. I wish Springfield made a 10mm. They made the best one of all, the OMEGA, and then they got out of 10mm altogether. A 200gr 10mm slug going 1200-1300fps is very satisfying.

    Hey, I found some Brian Pearce load data online:

    http://www.loaddata.com/members/search_detail.cfm?MetallicID=6607
     
    Last edited: Oct 17, 2014
  11. cloaker

    cloaker Lifetime Supporting Member Lifetime Supporter

    44
    0
    0
    I think once I know what I'm doing, that casting would be the next step simply because I think it makes you that much more confident on what you put in your weapon. I kind of think of reloading like cooking, you can just follow the recipe or you can understand the recipe. I think it would be very satisfying to make your own bullets. I am going to check out that load data right now, thank you very much!

    Dave