strange pressure issue

SPAK

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Minuteman
  • Apr 3, 2009
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    U.S
    Hey guys,

    I was doing a load development today and ran into an interesting pressure issue. Load development is with H4831sc, lapua brass, 208 gr Amax, cci 200 primers in .30-06.

    After I was done with the load development part of the shooting session, I decided just to run through 20 rounds of practice shots with a known load for my rifle: .30-06 57.0gr RL22, Lapua brass, cci 200 primers.

    First round fires no problem, but case ejects with a ton of soot all over the case, and slight EJ mark.

    Second shot goes down, also very sooted case and another EJ mark and stiff bolt. Case head also has raised burr from the ejector cutting into the case head.

    Ok, so by now I'm wondering either I mischarged my cases, or maybe there was some case lube on the brass that I didn't get all off. Both of which are not likely.

    So, 3rd shot goes down, brass not as sooty but still have a slight EJ Mark.

    Against my better judgement I keep shooting. 4th shot Case not as sooty again, less EJ mark than before.

    Long story short, after 6 rounds the pressure signs normalized without any signs of overpressure. It took the first 6 rounds of what seemed to be overpressured rounds for the pressure signs to go away. Stupid to keep shooting, yes, probably. But something just wasn't adding up.

    I've shot this load of RL22 57.0gr for well over 1000rounds without any problems before. I've shot it after shooting rounds with RL 17 before and also not have had any problems.

    The only thing different in this session was I put rounds down range loaded with H4831sc without running a boresnake or cleaning the bore.

    I would have beleived a change in accuracy based on what I've read and what I have heard others tell me before, but I wouldn't have expected an increase in pressure for the first initial rounds and then pressure returns to normal.

    For what it's worth, during initial load delvelopment I hit pressure at 58.5gr of RL 22 in 65 deg temps with the 208 amax.

    Shooting today was done in 14deg weather.

    Anyone have any thoughts???
     
    Re: strange pressure issue

    No pics, but high pressure as witnessed by ejector marks should show a full circle raised area where the brass is forced into the ejector hole. How flat the primers are, is also something to look at, but not a reliable indicator of pressure.

    A sooty case is a sign of low pressure, or incompletely burned powder.

    My guess is that due to the low temperature, the CCI 200 is not fully igniting the slow RL 22. As the barrel warms up ignition is better.

    CCI 200 is a mild primer...You might get away with it in warm weather in a 30-06, but I would use a Magnum primer, specifically a Fed 215, (that's the only Mag primer I use), or a Win standard LR primer with any RL 22 load in all temps.

    Win standard LR primers are actually hotter than a standard primer to better ignite ball powder. It's a pretty good all-around primer, really. In the '06, I switch to a 215 with 4350 in cold weather, and 4350 is faster and a <span style="font-style: italic"><span style="font-weight: bold">lot</span></span> easier to ignite than RL22.

    Anyhow, it's just a guess, a chrono would provide important info to help tell the tale.

    If you do decide to try a mag primer, drop the charge weight by 2 grains to start.

    TC
     
    Re: strange pressure issue

    Shots were done over a chrono today, but I had a lot of errors due to it being very sunny and the angle from where the sun was shining from. The few numbers that I did get all ran at expected velocity right around 2690-2700fps (including the loads with h4831sc) Velocity seemed to be right on what I expected, but there's no way for me to know for sure because I had so many error readings.

    Also, my barrel was warm, not hot, but warm since I just finished shooting my H4831sc loads.
     
    Re: strange pressure issue

    I see what your saying now top cat about the ammo being cold regardless...The only thing is this isn't the first time I've fired the RL22 load in the colder temps...I've fired under colder conditions as well. I did lose velocityas expected, but I never experienced sooted cases like this or the pressure signs before today.
     
    Re: strange pressure issue

    I found this on my googlefuing today...I don't have a seirra manual so I can't confirm. This was taken from another shooting forum...

    "From a Sierra chapter:

    Powder residue sometimes reacts very badly to a second powder being fired in the same barrel without cleaning.............................
    ..........................it frequently takes several shots before the second load will settle down and begin shooting accurately. If the powders were dissimilar, such as a double-based ball powder followed by a single-based tubular powder(or visa versa), this settling problem will be even more pronounced."

    As far as I know h4831sc and RL22 are both stick powders, but I don't know if they are that dissimilar that one residue would induce higher pressures for a few firings before normalizing....