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Thread: sooty brass

  1. #1

    sooty brass

    havnt done much reloading but have 2 loads for .243 (70 balistic tip over 39gr h4895 and 100gr spbt over 33gr h4895) both accurate and brass comes out ok no pressure signs etc. been given some h4350 and loaded up some rounds of 100gr spbt used the same preping sizing trimming and seating as the other two rounds and loaded up from 38gr.
    Velocities were as one would expect accuracy so so for 1st group 2nd and 3rd opened up alarmingly 4" at 150yds. The brass was sooty? no signs of excess pressure on primer. what the main cause of this? doesnt happen with other loads with identical brass, heads and prep?


  2. #2
    Soot on the outside of the case? Could be low pressure, the case is not expanding to seal against the inside of the chamber?...

  3. #3
    What cases are you using?
    I used Accurate Arms 4350 (very similar burn rate to H4350) with RP cases for quite some time with no sooting then I switched to Lapua cases using the same powder charge etc I had sooting all the way down the case.
    Lower charges made it worse.
    Upped the powder charge by 0.5 grains and the sooting stopped half way down the case.
    Upped again by another 0.5 grains and the sooting stopped half way down the shoulder.
    In the end I had to load the lapua cases with 1.5 grains more powder to get them to seal in the chamber.
    Obviously only increase powder charges with care keeping an eye out for signs of pressure
    Last edited by bbrc; 21-07-2010 at 20:18.

  4. #4
    I had the same problem with my 6.5x55, it stopped when I increased the charge or decreased the OAL.

    My Hunting Blog: click here

  5. #5
    I suspect as others have said that this is almost certainly low pressure rather than high pressure.

    Starting with book minimum loads from one reloading manual I found that I was getting soot on my cases and I'd worked up to max before the problem cleared up. I then found another load, in another manual, that started at the max load as printed in the first manual, when I worked up this load I got to the book max with no pressure signs. So, I guess it is true that rifles are all different and you need to keep your wits about you.

    It is said that very low powder loads can lead to something called secondary detonation which can cause a big pressure spike and blow up the rifle. Now, I've no idea if this is true or not but I think the bottom line is that low pressure loads can be as risky as excessive pressure loads and it is worth keeping it between the hedges.

  6. #6
    Compare the case capacities by filling with water and weighing the water. Odds on the new cases have a greater internal capacity . Bigger volume means lower pressure with the same powder charge so upping the powder will bring the pressures back to where the smaller cases are with the lower charge. check the case capacity first though.

  7. #7
    Nicely described Kev.
    (The Unspeakable In Pursuit Of The Uneatable.) " If I can help, I will help!." Former S.A.C.S. member!

  8. #8
    I had a guest 'rifle' at one time who used a Mannlicher stutzen in .243. His stags were always killed with exactitude, but his extracted, (reloaded), cases were always sooty on the neck and shoulder.

    His fired primers were plump and not filling the primer cup. Not enough pressure to seal the chamber, but his rifle was accurate with that load, and it killed.

    Sometimes a rifle will tolerate a lighter load and deliver accuracy - and in this case - killing; which is after all what the business is about.

    Some rifles will, however, deliver the goods after a 'dead' spot, just like an old fashioned carburettor, and after moving up a grain of powder or two in the cartridge, (as long as the primer does not show signs of stress by being unduly flattened or punctured), the rifle will settle down to excellent grouping again without backblow pressure in the chamber.

    The neck of the case has to seal the wall of the chamber before the gasses blow back. It's as simple as that.

    One little thought. Case cleaning can become a bit of a fixation. Make sure that the cleaned case is left with as close to a factory textured surface as possible and not shining like a regimental cap-badge. The case needs to grip the chamber wall in order to create a sure seal and assist in helping the bolt to contain the rearwards pressure.

  9. #9
    Absent minded as usual, I forgot to reinforce caorach's comments on how to blow up your rifle.

    It's been a point of sometimes heated discussion and opinion for years, but the advice is :- do not reduce the quantity of magnum or slow burning powder in cartridges which use such powders, below a certain point, or you are liable to incur detonation rather than the controlled burning which is desired.
    Detonation can have detrimental effects in nose-picking capabilities for the future - or the ability to scrutinise page three !
    This subject lies within the shadowy realms - at least it used to in my earlier years of reloading when I used a mallet to drive the bullets home, but I have not heard since if the matter has been resolved.

    One argument was that a greatly reduced measure of slow burning powder created too great an oxygen-to-nitro mix in the case which enabled instant detonation instead of a controlled burn.
    I simply do not know, but I do know that it is wiser to be sure than to take unwise and needless risks.

  10. #10
    I have read a little on the US NRA's studies on detonation, as well as those from the Aberdeen Proving Ground for the US Army and it is a gray zone. In any event, while they have yet to figure out exactly the physics inside the case at ignition, the results (tho rare) are pretty well documented. It is generally believed that light charges of slow power lay horizontally in the case and on ignition, provide an enlarged burning area of powder to ignite. As Eco says, excessive pressure ensues and the bullet becomes an obstruction causing a rifle to burst.

    With all that said, it makes me a little nuts to hear shooters say "Stay away from the lower end of the reloading data: you could blow your rifle up!" It is simply not the truth and unless otherwise noted**, most reloading manuals advise starting at 5-10% below minimum charges and work up; and that includes slow burning powders. You must be well below that level to even worry about detonation. Starting loads can leave sooty cases when a slower powder is used. It does no harm.

    I shoot more reduced (slower than even starting loads listed in manuals) than full power loads in my rifles. It is easy on the brass, easy on the gun, and easy on my sissy shoulder! I reserve full power loads for the field. Reduced loads are accurate and inexpensive when assembled with proper components. JMHO~Muir

    (** Some pistol powders, for example, are never to be reduced from starting listed loads)

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