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Thread: Burn rate / velocity / pressure / accuracy

  1. #1
    Member mopheadrob's Avatar
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    Burn rate / velocity / pressure / accuracy

    Hey guys. School me on this please.

    I get the relationship between pressure and velocity, and between velocity nodes and accuracy. I'm not sure how burn rates factor in to this.

    Here's my question. I'm out of the powder I've been using for my 7WSM (W760), can't find anything equivalent but have plenty of AR2213sc. The burn rate is obviously different, but from what I have read it should be okay in the WSM. If I switched, would I have to start load development from scratch and find a new node, or could I estimate a charge that would give me a similar velocity and fine-tune from there?

    Cheers, Rob

  2. #2
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    You will have to do load development again.
    I would start with the same COAL that worked with the other powder and go from there. You could try to aim for a similar velocity and see if it works out, it may or it may not, but obviously work up to it and start at the recommended starting load for that powder / projectile weight, just to be safe.
    There really isnt any reason to think much about burn rates. Its sort of just useless information IMO. Unless you get down to a barrel thats only a few inches long, the powder that provides the most velocity in a long barrel will also provide the most velocity in a short barrel.
    veitnamcam, Moa Hunter and dannyb like this.

  3. #3
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    A burn rate chart is only useful to find another powder that is similar to the one you are using.
    When changing power or projectiles always redo you load development and do another ladder test.
    Also look at Hodgdon superprofrmance powder as a replacement i load that in a number of cal including 300WSM.

    Sent from my CPH2145 using Tapatalk

  4. #4
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    If you subscribe to the OBT method, different powders cause different pressure curves, which means different barrel times which moves where the nodes are to different muzzle velocities.
    Resident 6.5 Grendel aficionado.

  5. #5
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    I think it’s in this video Scott Statterlee talks about different powders and velocity nodes. However he’s not chasing benchrest precision. His load development method is in reverse, and very frugal on components.

  6. #6
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    Quote Originally Posted by mopheadrob View Post
    Hey guys. School me on this please.

    I get the relationship between pressure and velocity, and between velocity nodes and accuracy. I'm not sure how burn rates factor in to this.

    Here's my question. I'm out of the powder I've been using for my 7WSM (W760), can't find anything equivalent but have plenty of AR2213sc. The burn rate is obviously different, but from what I have read it should be okay in the WSM. If I switched, would I have to start load development from scratch and find a new node, or could I estimate a charge that would give me a similar velocity and fine-tune from there?

    Cheers, Rob
    Greetings @mopheadrob,
    I sense from your post that a long load development for your new powder is not something that you are looking forward to so have a few suggestions that you may wish to try. You hopefully already have chronographed data with 760 so you will have an idea of how your rifle matches the 760 data. This should allow you to shorten the work up process. I would suggest that you chronograph the start load for AR2213SC and see how this relates to the Hodgdon/ ADI velocity data. You could then work up to the same velocity (corrected for your barrel length) as your current load in larger steps than usual and begin your search for a node around that point. I could never see the point in looking for accuracy at a velocity level that you would not be happy with. In my experience the best accuracy often occurs close to max loads.
    Regards Grandpamac.

  7. #7
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    You could try GRT and put in your old W760 data to see if the OBT nodes are accurate enough data to your real world results. You could then confidently apply any chosen powder to that.
    I could input it for you and give you the data. But it's not the same as doing it your self.

  8. #8
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    2213sc will be fine in your 7wsm...it's all I've used in the past 10 years, using 160 to 168 gr pills...pm me your phone number to dicuss loads..

  9. #9
    Member mopheadrob's Avatar
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    Thanks all! Great info as usual.

    You're on to it @grandpamac - I don't really want to step up from a start load in tiny increments. The node for W760 was pretty anaemic, not far off max recommended but under 3000FPS. I'm hoping for faster with 150 grain pills, and max for AR2213sc should give me that. Will flick you a PM, @Hindquarters.

    I hadn't settled on a COAL yet, @ChrisW. This was going to be the next step, but I ran out of powder...

    I'll follow up on some of the other info people have shared (need to find out what "OBT" and GRT" mean) but this has given me some guidance to shorten up the process!

  10. #10
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    GRT is Gordons Reloading Tool, a free but very good ballistics program. You can input things like
    the case capacity
    the projectile
    how deep it is seated
    the barrel length
    The powder charge and type
    It will give you a very close simulation of the velocity to expect, the pressure ( more importantly over pressure)

    OBT is Optimal Barrel Time ( the optimum to achieve a good harmonic balance of the bullet traveling down the barrel in time compared to the position of the barrel vibration as the bullet exits the bore. To some it is no more than a gimmic to others it is a method to follow.
    To me it is an aknowledgement I have sorted a good load but i dont rely on it alone

    By using GRT, once you have chronographed a load, and thus confirmed what is happening with the speed for a given charge . bullet / seating depth, you can then change any parameters in the program and see the outcome without firing more bullets, you can then load with what you have chosen and confirm results.

    Or you can do ladder tests and work up a load in the traditional method.

    Welcome to the rabbit hole!
    Last edited by johnd; 01-07-2022 at 08:00 PM.

  11. #11
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    Quote Originally Posted by mopheadrob View Post
    ..The node for W760 was pretty anaemic, not far off max recommended but under 3000FPS. I'm hoping for faster with 150 grain pills..
    If it's not over 3150, I'd be disappointed. I get that easily with my .280AI.

  12. #12
    Member mopheadrob's Avatar
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    Quote Originally Posted by 6x47 View Post
    If it's not over 3150, I'd be disappointed. I get that easily with my .280AI.
    Exactly. Wasnít far off with my .270!

  13. #13
    Member mopheadrob's Avatar
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    Quote Originally Posted by johnd View Post
    By using GRT, once you have chronographed a load, and thus confirmed what is happening with the speed for a given charge . bullet / seating depth, you can then change any parameters in the program and see the outcome without firing more bullets, you can then load with what you have chosen and confirm results.
    Thanks, thatís exactly what I need!

  14. #14
    sneakywaza I got
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    Quote Originally Posted by mopheadrob View Post
    Hey guys. School me on this please.

    I get the relationship between pressure and velocity, and between velocity nodes and accuracy. I'm not sure how burn rates factor in to this.

    Here's my question. I'm out of the powder I've been using for my 7WSM (W760), can't find anything equivalent but have plenty of AR2213sc. The burn rate is obviously different, but from what I have read it should be okay in the WSM. If I switched, would I have to start load development from scratch and find a new node, or could I estimate a charge that would give me a similar velocity and fine-tune from there?

    Cheers, Rob
    .270 Wsm is pretty close to 7mmWsm, I developed the load in my boy's .270 Wsm :150 Berger with 2213Sc, mild load going 3000fps, scope to easily get another 100fps without loading hard - you will be fine with 2213, stick to your current coal and start load at ADI max. Burn rate can be a red herring, especially when it's not comparing apples with apples, like stick vs ball.
    Micky Duck likes this.

 

 

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