Load development ?

Discussion in 'Reloading' started by Red hunter, Apr 28, 2012.

  1. Red hunter

    Red hunter Well-Known Member

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    Sometimes there are thing that make you go HMMM??
    I was asked a question the other day and it has me going HMMM?? Maybe you got something there.
    Here it is... When you do your load development do you let your barrel completely cool ? What if it is a load you are working on for tournament shooting when you have "x" number of rounds to fire in a set time period? Do you think that it would be better to shoot your rounds for load development the same as you would for a shoot with a set time limit where your barrel is going to heat up anyway and shoot a higher number of rounds at each powder charge?

    What do you think?
     
  2. muleman1953

    muleman1953 Well-Known Member

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    Hmmm
     

  3. Mikecr

    Mikecr Well-Known Member

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    I develop and test loads -as used in the field.
    It doesn’t mean I have to shoot 5-10 shot strings at each iteration of change, when 3 round-robin will get me in the ballpark. But eventually I’ll need to confirm that I can do EXACTLY what’s needed.
    For group shooting competition, I would develop with appropriate barrel cooling to prevent unnecessary damage(30-60sec shot rate for mid size cartridges), and then tweak the load to produce needed group quick enough for conditions. This, off the bench rest and bags that will always be used.
    For cold barrel accuracy, I use 30-60sec rate in development, and then tweak for results needed at far lower shot rates(like days, hours, and finally 10mins[the very worst in performance]). This, off a bipod in calibrated dirt.
    (just kidding)
     
  4. Alan Griffith

    Alan Griffith Well-Known Member

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    Just had 7mmRHB fix a few issues that the custom builder botched on my 6.5x47. 7mmRBH asked how I was going to shoot my rifle; meaning how fast or how hot was I going to allow it to get. He likes to place a pad or upward pressure under the 1st 1" to 1-1/2" of barrel to dampen vibrations. This is better for accuracy but can start to destroy it if one lets the barrel heat up. I asked him to place the pressure pad as this rifle was built for hunting and should not see any sustained heat in the barrel. Well, just the other day while working on some load development, I would shoot 3 sets of 15 shots in 5-shot increments. The first 5 were from a cold barrel. I would then go on to shoot the next 5 while the barrel would stay warm and the next 5 not letting barrel cool at all. It got hot. The groups were as follows.

    6.5x47 Lapua
    Nosler 140 gr CC
    40.3 gr H4350
    CCI 400

    These were 5-shot groups but I marked the best 4 and then 5th shot.

    CCI 400 2825 av Cold .42"/.9"
    3.130" dead 22 ES Warm 1.2"/1.2"
    15 shots 5 SD Hot 1.1"/1.84"
    2.89 bushing

    CCI 400 2831 av Cold .66"/1.17"
    3.130" dead 36 ES Warm .57"/.82"
    15 shots 8 SD Hot .7"/.88"
    .288 bushing

    CCI 400 2827 av Cold .78"/.84"
    3.130" dead 31 ES Warm .86"/1.02"
    15 shots 9 SD Hot 1.3"/1.63"
    .287 bushing

    7mmRHB suggest total free float if the barrel is expected to get hot.

    Alan
     
  5. Mikecr

    Mikecr Well-Known Member

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    Two questions Alan;
    What temp do you NEED the gun to shoot at?
    Why are you adjusting bushing SIZE?
     
  6. Alan Griffith

    Alan Griffith Well-Known Member

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    I had been using the .289" bushing which gave me .001" neck tension. 7mmRHB suggested a tighter bushing, saying my groups might tighten up with around .004" neck tension. I happened to have the two next smaller bushings so what I posted is the results of the test. A side result was the increased heat test.

    I was shooting at 65 Deg F but I'm not sure it matters. Keep the barrel as close to ambient temp as possible. I was shooting the "cold" groups with 2-3 min between shots. The "warm" temps about 1 min apart and the "hot" temp groups as fast as I could run the bolt, reacquire the target and squeeze the trigger.

    Alan
     
  7. Mikecr

    Mikecr Well-Known Member

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    A tighter bushing doesn't change tension. Sizing LENGTH does this.
    By temp needed, I meant will you need the barrel hot/med/or cold in the field?
     
  8. Alan Griffith

    Alan Griffith Well-Known Member

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    I agree, a smaller busing does NOT increase tension. Some folks just prefer to see it that way:)

    Cold or ambient temp. The groups were tighter with a "cold" barrel.

    Alan
     
  9. rscott5028

    rscott5028 Well-Known Member

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    I agree. .003", .002", .001" below caliber doesn't change tension. But, .000" does.

    Is he talking .001" before or after springback?

    A bushing that sizes to .001" less than caliber can be a problem if....

    (a) your measurements and/or neck wall thickness aren't accurate/consistent and you end up with some that are really about .000" below caliber

    (b) if your neck walls begin to thin and/or need annealing after numerous firings and you end up around .000" with some

    -- richard
     
  10. Mikecr

    Mikecr Well-Known Member

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    That's true Richard, and I should have qualified my reply specific to Alan's message.
     
  11. rscott5028

    rscott5028 Well-Known Member

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    Well, I knew that you knew. But, it's not obvious to everyone.

    Like many things it was a lesson I had to learn the hard way.

    -- richard
     
  12. Rem700

    Rem700 Well-Known Member

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    I like to let the barrel get as cool between loads/groups as possible. But i like to test loads to the conditions as close to what it will be used in (cold/hot). I also try to use powders that aren't affected by temp changes but the barrel is always a different story since it's metal and always affected by temparture changes.

    I would just test load at 5 shots, your going to have loads that your gun is not going to like and seems to be a waste of time loading more than that when the first 5 would be enough to show it doesn't like it. I do think it would be wise to shoot the amount you'll have to shoot in a competition to find out how your gun will group going from cold bore to hot after you got a load that the guns likes....IMO.
     
  13. Mikecr

    Mikecr Well-Known Member

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    With barrels I've developed for, which are med/heavy straight taper contours, there is some bore change with temperature transients(heating up).
    The barrel heats from the bore outward and initially the bore is confined to expansion -inward, as the outer area hasn't yet sunk the heat to a stabilize dimensions. The colder outer area is not allowing the hotter bore to expand as much as it wants to(outward), so the bore expands inward(constricting) until it can finally swing outward(always least resistance). With this, performance can change.
    But atleast in IBS & NBRSA you get a sighter period to freshly foul and bring the barrel to stable temps.
    I can't imagine a competitor not utilizing this opportunity, given that everyone else is.

    I'm not a competitor, but if I were, I would work out a prefouling and heat-up rate for that sighter period that provides the best results in record shots. There would always be a timer on my bench/rest.
    You can't load develop with all this change though. You really need to get the bore stable before testing.
     
  14. bowhunthard

    bowhunthard Well-Known Member

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    Please clarify... I'm in no way new to reloading, but I am new to bushing dies :D. I thought bushing size was how you changed neck tension, and how does .000" change anything?