Secondary Explosion Effect? Or.....?

Discussion in 'Rifles, Bullets, Barrels & Ballistics' started by 307WYO, Sep 16, 2013.

  1. 307WYO

    307WYO Member

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    Any help, advice, or ideas would be greatly appreciated... So here's the details, I'm shooting a 7mm ultra mag. I shot a 0.5" group yesterday with 88 gr RL-25, one fired brass, federal 215M primer, and 140 gr nolser accubond. Went home and loaded another 5 rounds identical but with new remington brass. It resulted in big dents being left right in front of the case shoulder. There was burned powder on the outside of the case like gas entered between the chamber and the case. What I have read on this subject and thd secondary explosion effect leans towards the idea that the load is too light.... I then shot even a lighter load (87 gr) in a once fired case and everything was fine. Also tested it with the same load from the day before...... Long story short, the big dented cases were replicated 3 times, all with new brass. Anytime once fired brass was used, everything worked great. Could it be a bad batch of brass or is the once fired brass stronger and can withstand more? Any help would be great. Thanks everyone
     
  2. 307WYO

    307WYO Member

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    Here are some pics of the cases.
     

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  3. wbm

    wbm Well-Known Member

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    The load is too light. For you and your rifles safety I would never shoot that load again.
     
  4. Max Heat

    Max Heat Well-Known Member

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    That's exactly what I shoot, except that I run Hornady SST's (139gr). I've never had any cases that came out looking like that though. I did try some loads in the 80's, but 90-93 grains seems to work best, for RL-25. Tomorrow I plan on trying out my first RL-33 loads.

    The issue that I have found with fresh rem brass, is that there is a "lip" on the inside of the neck, that doesn't want to go away, no matter how many times the brass is run through the sizer/expander die. I have a 3-way cutting head on the trimmer, but the fresh cases come up too short for me to want to trim them, until after they have been shot at least once. Basically, they need to be shot once (fire-formed, if you will), to convert that lip into more length. After that, they become pretty decent brass.

    Try working the fresh cases through a sizer/expander die at least a dozen or more times, before they are shot for the first time. See if that takes care of the problem.
     
  5. Lefty7mmstw

    Lefty7mmstw Well-Known Member

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    When I was loading for my 7rum I was at 95 grains rl25 with the 140 sierra. Even with the nos. being stickier in the bore I'd go to 93 or so. This round doesn't like to be underloaded very much.
     
  6. Max Heat

    Max Heat Well-Known Member

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    You may also want to try seating the bullets deeper into the cases. The 7RUM internal pressures are difficult to control, if loaded too close to the rifling lands.

    I'm leaning AGAINST believing that your problems are due to running loads that are too light, because I have loaded all of the way down to 75gr without issue, for purposes of directly comparing performance to my 7RM using the exact same loads. Just for the record, the 75 gr loads fell way short on velocity, compared to the same loads in the RM. But also, you state that once-fired brass does not ever exhibit the problem.

    You aren't trimming/chamfering, or de-burring, the ID of the never-fired cases before you shoot them once, are you?
     
  7. 307WYO

    307WYO Member

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    I have shot this exact a lot in my other ultra mag as well as my brother for at least a couple years now. Like i said earlier, for some reason this is only happening with my new bag of brass. With 88.4 grains of RL-25, that is in the middle of the charge window according to the book. So i would think there should be enough pressure to expand the case enough to seal. I am FL sizing the new brass before their first load just to try to get some consistently in my brass. Should i not be sizing them prior? Thanks for all the help everyone.
     
  8. LONGSHOOTER

    LONGSHOOTER Well-Known Member

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    Try sizing only 2/3 of the neck on the new cases, and no further.

    If it were me, I would size the neck up to .308, then partial size most of the neck down to 7mm. This would create a false shoulder on the neck, to seal the neck in the chamber. This can also help if there is excessive head space present.
     
  9. LONGSHOOTER

    LONGSHOOTER Well-Known Member

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    ...
     
  10. Max Heat

    Max Heat Well-Known Member

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    In addition to having that significant lip on the inside of the neck, the virgin rem cases are ALSO "wavery" around the neck's diameter, most likely a result of down-necking/annealing the 300RUM parent cases. You definately need to run virgin rem brass through the sizer/expander die [numerous times], BEFORE doing anything else to them, in order to get the neck diameter trued. And I would advise against trimming them. I just pulled a random sample of 5 virgin cases out of a box, and miked them up. They come up between 2.8425 and 2.845, while the spec indicates [max] length should be 2.850. You should strive to be as close to that as you can get, in order to get the best possible seal around the neck, for minimizing the possibility of any high-pressure gasses from getting past/behind it. If that inner lip really bothers you, try chamfering it out very lightly, making sure that the case does not loose ANY of it's length.

    If that doesn't solve the problem, the fault must lie with the chamber, such as mis-alignment to the bore. If you still experience the phenomenon after trying all of the suggestions [including using hotter charges, for breaking in the cases], then HAVE THE RIFLE CHECKED OUT BY A SMITH.
     
  11. 65WSM

    65WSM Well-Known Member

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    I have not loaded a lot of Reloader 25. I did have some mysterious detonations with the .264 Winchester Magnum with R-22. I got rid of my two .264s before R-25 came out. I switched to the WSM case and tend to use Retumbo rather than R-25 with similar performance.

    The Reloader 22 was leaving fumes in the barrel after firing in my .264 (again 2 different rifles). The fumes were detonating outside of the case with the next round if I did not blow out the barrel. I used a blast of canned air to clear the barrel. I had dents in the shoulder but not back onto the shank of the case. Compression would detonate the fumes when the case expanded to fill the chamber. Because it was a belted magnum, there was more room between the case shoulder and chamber. The Reloader 22 and 25 are Bufors powders with a lot of nitroglycerine and a lot of retardant to make them slow. I do not seem to have fumes from ADI Retumbo or Vithavuori powders. I will have some "Norma" 217 to play with tomorrow. It is the same powder Norma uses in the .30-378 Weatherby ammo. It does produce 3400 fps with 180 gr bullets, I have chronographed it my self. I do not know where it is made. I would guess it it a Bufors powder and may have similar problems.
     
  12. Lefty7mmstw

    Lefty7mmstw Well-Known Member

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    I've never heard or seen this one, and I burn rl22 and rl25 by the keg in more overbore cal's than the 264. Sounds like something else going on with your reloads other than powder issues.

    rl22 likes to build pressure rather slow if you don't have enough pressure and/or don't have enough load on it. Underigniting with a standard primer can do this too. The fumes( really smoke) have no more ignitability than air (the powder's already burned) so I'd suspect you are simply getting blowby occasionally on the next round.
     
  13. Joe King

    Joe King Well-Known Member

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    My thinking is that for what ever reason the neck didn't hold those bullets securely allowing them to be dislodged by the primer. What's leading me to this is that the dents are right where the gas hole should be on your receiver, and (IF) the bullet exits the case mouth before preasure builds what would stop the gas from finding another exit (by leaking past the neck and shoulder to the gas hole). Pressure obviously went up at some point, you can see that on the case. Just a thought.

    I think the issue lies with your new cases though. Maybe you might think about annealing the rest of that batch of cases, and resize them before you load any more of them.
     
  14. Mikecr

    Mikecr Well-Known Member

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    Any ideas as to how gas outside of a case would be higher than gas inside a case -to cause indention?
    It's just hard to picture perfect local pockets somehow higher in pressure at any point of internal ballistics. Could it be powder blowing by? But then, why a pocket of it?

    I can picture gas blowby preventing a case from good enough chamber grip, extending case length. But that's it.