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IMR 7383

ladamsladams Member Posts: 604 ✭✭✭✭
edited February 2008 in Perry Shooter Competition Shooting and Reloading Forum
I have about 25 lbs of this stuff sitting in my cabinet. I used to use it all the time for my 30.06 with great results. Terrific accuracy, low recoil, modest velocity and no muzzle flash. Then I read some things about how it can be prone to secondary ignitions which will blow the barrel. Anyone use much of this stuff, and have you ever actually known of any proven instances of secondary ignition? I would love to go back to using it, but am being cautious.
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Comments

  • sandwarriorsandwarrior Member Posts: 5,453 ✭✭✭
    edited November -1
    ladams,

    I'm thinkng you might be referring to IMR7828? The issue you are talking about is usually associated with a less than 70% full case in which the primer ignites the rear of the powder column but at the same time jumps forward and ignites the front of the powder column. the effect of this is that the two ignited columns of powder meet in the middle of the case where pressure maximizes instead of progressively burning the powder out the end of the barrel.

    As noted this happens with low volume loads of slow burning powder and is more prone to happen in the cold where the slower powder is slower to ignite. This powder isn't inherently dangerous. Just the way that people load it. The reloading guides have a minimum for a reason. You should stay above the minimum when starting out a load.

    In the case of a 30-06 you probably couldn't get less than a full load of powder into the case unless you were shooting very heavy bullets.
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  • ladamsladams Member Posts: 604 ✭✭✭✭
    edited November -1
    It is definetely 7383... it is a surplus powder that used to be very common and inexpensive a few years ago. But I have heard that the secondary ignition usually occurs with a under filled case.
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  • sandwarriorsandwarrior Member Posts: 5,453 ✭✭✭
    edited November -1
    ladams,

    I did a further search and you are correct. There is such an animal. So far what I can find is it is 50BMG ammo. It's described characteristics are it doesn't like any airspace and doesn't like compression. Those are only opinions of it that I've found.

    It sounds like it has a hard time igniting. Therefore a very slow burning powder. The 70% rule may bump to 80-90%. And even though it is a slow burning powder it seems as it's a high pressure powder(double-base, Nitro-glycerin added). Therefore, causing a large spike in pressure when ignited in a compressed load. From what I can see about it, it is a tough powder to load without solid data on where the safety bandwidth is.
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  • JustCJustC Member Posts: 16,056 ✭✭✭
    edited November -1
    "secondary ignition effect" occurs when too low of a voulme of powder is used (usually someone trying to make use of a fast powder they had laying around) and upon being an acceptable or max load, is still less than say 60% of the case volume when layed down horizontaly (chambered). Picture a case with only a 50% load density, then envision the powder settling in the case as it is chambered. The powder settles along the axis of the internal volume,..with me so far? Now, picture that primer pocket/flash hole being directly along that axis since it is in the middle of the case. When that primer is lit,..and that spark jumps through the flashhole, it will ignite across the TOP HORIZONTLE SURFACE of the entire load since the load is just barely up to that flash hole. The spark being able to jump across the entire top surface of the powder charge, rather than igntiting the BASE of the powder column in a properly dense load, will ignite more surface area instantly and change the burn rate/characteristic of the load and powder. That instantaneous ignition rather than the correct ignition of the charge at the base of the column and allowing it to burn fwd in a controlled (burn rate) manner, causes a massive pressure spike not only in P.S.I., but in time of reaching that pressure (what is knows as a sharp pressure curve) and this overcomes the ability of the surrounding steel to contain the pressures. The bullet is begining to move down the bore,..but the pressure curve is so sharp, the bullet can't move fast enough down the bore to increase the internal volume to a point where that pressure decreases enough to NOT cause a failure. basicaly,..the bullet can't get out of the way fast enough....

    Always be careful using faster powders than are recommended by load books or when at near max,..still won't fill at least 70% of the case. I error on the side of caution when "interpolating" load data.
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  • nononsensenononsense Member Posts: 10,928 ✭✭✭✭
    edited November -1
    ladams,

    There is nothing wrong with using IMR-7383 so long as you understand when and how much to use. Originally it was used in the .50 cal. Spotter-Tracer cartridge.

    It is a triple based powder which means that it's made from the two basic components for double based powders, nitrocellulose and nitroglycerin but has the added component of nitroguanidine. Like adding nitroglycerin, nitroguanidine adds an increased energy to the powder configuration. It also makes the powder flashless or as close as possible, which is an obvious benefit when shooting under low light conditions.

    Being a triple base powder makes it an oddball in our world of civilian reloading. It also makes it tricky to load. Basically, it runs somewhere around IMR-4064 to IMR-4320 but this powder can show a 'spiky' characteristic. One load will be fine then the next small increase will show a significant increase in pressure out of proportion to the increase in powder.

    S.E.E. or Secondary Explosive Effect is a potentially dangerous condition that is created by low volumes of smokeless powder used in large capacity cases. Instead of the powder being lit as a column at the base, it's ignited across the entire top surface as it lays in the bottom of the cartridge case when held horizontally to fire. This is a very controversial topic and you need to read several opinions about this. The 'explosive experts' have one opinion while the ballistics folks have another. It makes for very entertaining reading.

    The guideline for avoiding this condition is to keep your case fill above the 80% mark, in my opinion. I try to balance my loads to the maximum fill of 100% or as close as possible. This increases consistency from shot-to-shot while avoiding the potential for ignition problems.

    My last suggestion is to call, or e-mail Hodgdon/IMR and get one of their tech folks on the line and get some information from them.

    Best.
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