Pressure "spikes" on Big Magnum Cartridges....

Discussion in 'Reloading' started by kraky2, Oct 12, 2006.

  1. kraky2

    kraky2 Well-Known Member

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    Pressure \"spikes\" on Big Magnum Cartridges....

    Some of you guys shoot some big capacity cartridges. The weather is turning cooler here and I've kind of semi retired and have some time to try and work with my 30-378 I bought years ago but hadn't shot alot.

    HERE'S THE SITUATION....I'm at the range the other day finishing off a 6 mo. old batch of 200 accubonds over 118 grains bmg. My notes when I shot the freshly loaded batch said "shoot great" "velocity 3170. This in a stock sako with 26" barrel. Well today I shoot about 8 rounds and they are clocking about 3250....and I get one with a sticky bolt and one more with a realy sticky bolt. The sun was just getting high enough over my chrono where I didn't get readings on the sticky bolt shots.

    I stop there and go home with my last 3 rounds still loaded.
    I can't figure out what's going on. Maybe I missed trimming these last ones....no they check out ok. Then I get to thinking that in the past I had noticed that as ammo gets old the bullets sometime take a sort of "set" to the case. I thought I had cured this by swabbing out lube with damp paper towels wrapped around a small nylon bore brush.
    Anyhow I take the last three rounds and put them in my seating die and try to seat them deeper and sure enough....there is somewhat of a "crack" as they let loose.

    Have you guys ever experienced this kind of "bullet set" or bonding (if you will) on stored ammo? Am I crazy to think this can have any more effect than....say.....crimping?
    Is it possible my gun was just "fouling out" and that caused excessive pressure to come on that fast???

    ANY OTHER IDEAS PLEASE????????

    BTW--I checked a 6 year old batch of xlc barnes loadings and the coating sure keeps them from taking any kind of set.
    They seated deeper as if I was just loading them tonight.

    Maybe a couple of drops of flitz in my tumbling meadia is putting a coating on my brass that is "unfriendly" to storage of regular jacketed bullets?
     
  2. J E Custom

    J E Custom Well-Known Member

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    Re: Pressure \"spikes\" on Big Magnum Cartridges....

    Kraky

    First of all you did the wright thing by stoping.

    If all of those "old" loads were loaded at the same
    time and with the same batch of powder/bullets/primers
    I think the problem was heat.

    Older powders become heat sensitive (more volatile).
    But 6 months is not old.

    While competing in a 1000 yrd match I had the same
    thing happen to me.

    Started shooting and everthing was going very good
    but soon I started chaseing the bullet strike and ended
    up taking over 2&1/2 moa off before the problem showed
    its ugly head by blowing a primer.

    being a little slow on the uptake I proceeded to blow two more primers then I stoped .

    Laying there in the hot sun trying to figure out what was
    wrong I had an epiphany(brain fart)my ammo was in the sun
    and felt hot to the touch.

    So I laid there and used up about half of my time waiting
    for the ammo to cool down so I could finish the match.

    Sure enough after cooling it shot fine.

    Note: These loads were MAX and the heat only made them
    More so.

    Your loads were progressively getting hotter thats why
    I think this was the problem.

    Sounds like you are very particular in your reloading so
    heat would be one of the variables.

    Good shooting
    J E CUSTOM
     

  3. kraky

    kraky Well-Known Member

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    Re: Pressure \"spikes\" on Big Magnum Cartridges....

    Thanks for taking a shot at my problem but unfortunately we shoot out of nice, cool, shady, shooting shed and the ammo wasn't in the sun. I even found a record where I had loaded the exact same load a year earlier with no pressure problems (with the same lot of powder). I do trust my scale (rcbs1010) and I always double check the scale for the first few rounds against a digital scale so I know it was on the money. Heck with that big of a case even a grain more powder would only result in about 20-30fps.
    I did run a boresnake down the barrel before switching to this batch of ammo. Maybe I stirred something up in there that changed the friction inside the barrel and a near max load became nasty. I'd appreciate any other guesses but I am thinking somehow I got a spike of at least about 10k on the one shell. The primer didn't fall out but I'm thinking it had to be darn close to it and with that big heavy case I had to be way over max.
     
  4. Ridge Runner

    Ridge Runner Well-Known Member

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    Re: Pressure \"spikes\" on Big Magnum Cartridges....

    The barrel heating up will warm the ammo enough to do this, I've saw the same thing in my 7mm AM, leaving the third round in the chamber an extra 2 min. will boost my MV over 200 fps. but I shoot WC872 and its pretty heat sensative, on an 80 degree sunny day, a typical 3 shot string goes like this first shot is fine, light bolt lift, effortless extraction, shot #2, slightly heavy lift, slightly sticky extraction, mildly cratered primer, third shot, !@$%*& heavy bolt lift, and very sticky, primer may or may not pierce. 60 degrees and below there isn't a problem.
    JS
     
  5. kraky

    kraky Well-Known Member

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    Re: Pressure \"spikes\" on Big Magnum Cartridges....

    I can see how that can happen with a warm barrel--much like leaving the ammo in the sun. It was about 45 degrees this day and I was shooting by loading one at a time so the bullet was only in the barrel about 15 seconds. I'm going to back the loads down about 2.5 grains and see where "they clock". I'm expecting to lose only 50-60fps and hopefully get in a "zone" where I have a little lee-way for "crap happens".
     
  6. J E Custom

    J E Custom Well-Known Member

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    Re: Pressure \"spikes\" on Big Magnum Cartridges....

    Kraky

    I load 116gr of 50 bmg in mine and its healthy so 118 could
    be on the edge.

    50 bmg is very forgiving and does fowl but 8 ronds shold
    be no problem.

    You might try a real good cleaning and check freebore.

    When you find the problem please let the site know.

    It may save someone else from going through what you are.

    Good luck
    J E CUSTOM
     
  7. kraky

    kraky Well-Known Member

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    Re: Pressure \"spikes\" on Big Magnum Cartridges....

    JE----THANKS for the input. Does anyone care to share some successful loads with 165-200 grainers with the 30-378?

    Here is a sample pack I intend to load up this afternoon and get out and shoot soon. They are repeats of past loads or some new ones I'm speculating on.

    104 retumbo under 200 accubond
    101 Re 25 under 200 accubond
    105 Ramshot mag under 180 partition
    121 AA8700 under 180 partition
    109.5 H1000 under 180 accubond

    Maybe when I'm doing this type of testing (about 5-6 rounds of ea load) the mix of powders etc are fouling me out although the gun shoots good all the way through the test. My gun is one of the cheap sako TRG-s that was on closeout lists about 6 years ago for about $600. It's been a decent shooter.....not stellar...but decent. From what people say it has a terrible recoil lug that DOES NOT help the accuracy picture to much.
     
  8. keithcandler

    keithcandler Well-Known Member

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    Kraky extreme copper fouling can cause increasing ......

    pressure from shot to shot. I saw this once in a 6.5x55 Swede. We were loading at the range with my friend's 6.5x55. My friend fired a shot and we had to use a lot of force to get the bolt open. I pulled the bullets on his remaining loads and the loads were at the "starting" point in the Hornady manual. Upon inspection of the muzzle, the barrel looked as if it was gold plated. Twelve applications of Sweets later the barrel is clean. It amazed me to see how pressure sky rocketed because of the copper.

    If you do not have a good cleaning regiment that completely de-coppers your barrel, copper fouling could be the culprit.

    Good luck to you!
     
  9. Jimm

    Jimm Writers Guild

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    Re: Pressure \"spikes\" on Big Magnum Cartridges....

    "Cold welding " comes to mind .

    Long time loaded rounds will exhibit characteristics such as yours due to a " bonding of the bullet to the brass ( cold welding ) . A article in the latest Precision SAhyooter mag reccommmends final seating just before shooting .

    Jim B.
     
  10. kraky

    kraky Well-Known Member

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    Re: Pressure \"spikes\" on Big Magnum Cartridges....

    It wasn't the first time I'd noticed higher pressure on stored ammo. And, on another forum a guy complained that he had a super load for a gun that shot great when freshly loaded but terrible a year later.
    Did the article give any estimates on what kind of pressure spikes could possibly happen?? Can you give me the date of the article....I may try and find it.
    Thanks for making me feel a little more sane!
    Maybe crimping equalizes the whole phenominon a bit more than non crimped ammo??
     
  11. larrywillis

    larrywillis Well-Known Member

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    Re: Pressure \"spikes\" on Big Magnum Cartridges....

    If you measure your cases above the belt you'll see why your handloads are sticking in your chamber. They're not getting resized enough. It's a very common problem with all belted magnum calibers. Visit our website, and you'll see what you can do to solve this problem.

    - Innovative
     
  12. kraky

    kraky Well-Known Member

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    Re: Pressure \"spikes\" on Big Magnum Cartridges....

    LARRY--I actually have one of your dies. It works great on a couple of my friends custom weatherbies that seem to have somewhat "generous" chambers in the belt area.
    We "reclaimed" enough brass the first night of ownership to pay for the die and it has been very well built. BUT the problem I'm having isn't related to sizing.....it's related to "high pressure" loads.....very bright extractor marks etc. Besides....do you even make a die that would handle the 30-378??? That case is really built and I haven't had any trouble chambering after sizing.
     
  13. overbore

    overbore Well-Known Member

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    Re: Pressure \"spikes\" on Big Magnum Cartridges....

    Kraky, if your pressure spikes are from "cold welding", the "other choice" to prevent galvanic corrosion , falsely called cold welding, of the bullet and case is to use molly bullets as it is proven to prevent dissimilar metal contacts. Overbore
     
  14. larrywillis

    larrywillis Well-Known Member

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    Re: Pressure \"spikes\" on Big Magnum Cartridges....

    Kraky1,
    I doubt that you've had your ammo long enough to experience excessive pressures from bi-metalic corrosion, although I have seen it happen on ammo made during WW1.

    I'm glad to hear that you're using our Belted Magnum Collet Resizing Die for the popular belted calibers. Knowing this, I'm sure you understand the pressure ring above the belt. I'm 99% positive that it's causing your extraction problems. Measure your cases above the belt (and compare to a new factory case) and you'll know for sure.

    At this time it looks like I won't be making a collet resizing die to fit the huge Weatherby 378 case. However, I have a long list of customers that want one for their 378. Manufacturing is getting too expensive for me, but if enough shooters contact RCBS - they might have enough interest to lease or purchase my patent ( I sure wouldn't mind that ...)

    Also, if your hot handloads were made during the colder months - they could produce VERY high pressures during the summer months.

    - Innovative