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DPT Alpine


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  • 1 Post By mikee
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Thread: Jump

  1. #1
    Member
    Join Date
    Nov 2018
    Location
    Auckland
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    990

    Jump

    Hi All
    looking to develope a load for my 7rm using 160 gameking hpbt
    looking at 2225,big range of charge weights listed by sierra, 7.5gn approx
    and also 2217, even bigger range,like 10gn.
    ADI data is for 160 partition or 162 hornady spbt with about half of the
    range of charges(+-4gn) starting around the middle of sierra's range,going up
    So,would you,
    a)load 3 at 0.5gn increments right through the range,
    b)load 1 each at 0.5gn increments from start charge weight for the
    first say third of the range to just check pressure etc,then 3 at each
    0.5gn increment from there,assuming faster is better
    c)ignore sierra start point,just use adi data,load 3 at each 0.5gn increments.


    Also why does a 160 nosler partition have start charge of 4gn less than a
    162gn hornady spbt?

    You thoughts appreciated

  2. #2
    Member mikee's Avatar
    Join Date
    Aug 2012
    Location
    Nelson, New Zealand
    Posts
    8,425
    do you have plenty of 2225? There is not going to be any more available till end of year earliest apparently so if this is a new load you are developing would it be worth it.

    Projectile bearing surface has an impact on pressure and so that could be the reason for the range of charge weights over different projectiles of the same listed weights
    dannyb likes this.

  3. #3
    Member
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    May 2020
    Location
    Palmerston North
    Posts
    43
    I would suggest option B in the interest of saving powder (If powder is readily available A). I would stick with the Sierra data as there is no guarantee the Nosler or Hornady will behave like a Gameking pressure wise. As a side note the notation for grains is gr.
    dannyb likes this.

  4. #4
    Member G.I_Joel's Avatar
    Join Date
    Apr 2020
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    Wellington
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    I personally run 3 at each whole increment. Then fine tune 0.5 either side of the whole number once I’ve found “the one”
    Everyone’s different. Some will tell you run 5 at each increment, go into the 0.2gr details etc etc...
    I myself am new to reloading so from your options I would choose B.
    Go fast, Donít suck

  5. #5
    Member
    Join Date
    Dec 2019
    Location
    Okawa Hawkes Bay
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    914
    Quote Originally Posted by widerange View Post
    Hi All
    looking to develope a load for my 7rm using 160 gameking hpbt
    looking at 2225,big range of charge weights listed by sierra, 7.5gn approx
    and also 2217, even bigger range,like 10gn.
    ADI data is for 160 partition or 162 hornady spbt with about half of the
    range of charges(+-4gn) starting around the middle of sierra's range,going up
    So,would you,
    a)load 3 at 0.5gn increments right through the range,
    b)load 1 each at 0.5gn increments from start charge weight for the
    first say third of the range to just check pressure etc,then 3 at each
    0.5gn increment from there,assuming faster is better
    c)ignore sierra start point,just use adi data,load 3 at each 0.5gn increments.


    Also why does a 160 nosler partition have start charge of 4gn less than a
    162gn hornady spbt?

    You thoughts appreciated
    Greetings Wide Range,
    The Nosler 160 grain partition projectile has a much longer bearing surface than the 160 or 162 grain spitzer boat tail. This produces more pressure. You can see this by comparing the max partition loads with the start BT loads. As you are using a hollow point? boat tail Game King the 162 grain Hornady loads are likely more relevant. People get hung up on exact projectile weights when projectile type is more of a problem.
    If I was working up a charge for your rifle I would load 2 rounds each of the start loads and chronograph them. If the velocity is close to predicted in the data then pressure is likely to be as well. Next I would go up 2 grains and chronograph again. Still OK then up to 1 grain under max. There is absolutely no point to my mind in testing a whole lot of loads that you will not be happy with the velocity of especially when components are as short as they are at the moment. If it rings your bell however fill your boots. From this point up to book max you can fiddle around for the best results. 7mm Rem Mag loads are kept low due to the variation in rifles and pressure developed. Bear in mind also that a single group tells you little other than a big one is not much use. One tiny group can be a matter of chance. Three, three shot groups would be a minimum if you are testing for accuracy. I tend to work up to velocity and then test for accuracy. Saves a stack of components for later.
    Regards Grandpamac.
    Rated M for Magnum likes this.

  6. #6
    Member
    Join Date
    Jun 2019
    Location
    Manawatu
    Posts
    252
    If I'm trying out a new combo, I usually start 1 or 2 grains above minimum ( if it's a large charge weight range like you describe) and go up in 0.5 grain increments with one shot at each charge weight. I do this up to and 2 grains over book max, knowing I probably won't shoot the last couple.

    When shooting this ladder, I use a chronograph. I'm not looking for grouping but to see if the combo is viable for what I want to achieve, no point in good groups of you're only getting 280 rem speeds from a rem mag right?

    Or if I want one range trip, I'll load similar to your option b.
    Bit go in whole grain increments for the low ones, say first 3 charge weights, then when you're getting closer to the expected speed range you're chasing, go in 0.5 increments.

    I have found that doing the one shot at each charge ladders has saved me time and components when trying out new combos, especially when there isn't much data around for the combo you're experimenting with.

 

 

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