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Joined: Oct 2011
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imgoofy Offline OP
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I would like to try IMR 7977 in my 6.5x68mm using the 127 gr Barnes LRX bullet.

I have max load data from QuickLoad for Retumbo, IMR 7828 and H1000.

Are there any % conversions for any similar slow burning powders based on max load? I've sent a data request to Hodgdon a couple weeks ago and haven't received an answer from them. I sent another request this evening.

I'd appreciate any help on this little project.


Goofy aka graybird on other forums

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Hodgdon says it is most similar in burn rate to H1000. I would use that data to compare velocities. IMR7828 is a denser pattern so I don't know of a formula to develop the weights. I would work up a load with H1000 with tested data and use that as a base line for velocity. I would start about 5-10% lower with 7977 and work up to a similar velocity as the H1000 load while watching for any indications of pressure such as a drop or flatline in velocity per half grain of powder.

You can compare the two in similar sized cases to get a rough approximation of the ratio. In the 7RM 7977 was running about 4% higher than H1000. I would knock that back to 3% as a fudge factor and work up accordingly multiplying known H1000 loads by 103%. Please report back so we know that you can still type.


"When you disarm the people, you commence to offend them and show that you distrust them either through cowardice or lack of confidence, and both of these opinions generate hatred." Niccolo Machiavelli
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Maybe your QL hasn't been updated in a while. I think I bought my last update three or four years ago...there just isn't enough added each time a new update is offered to make it worth the cost IMO. Ayway, I found that my QL does include the Endurons so I ran it for you. I assumed a 24-inch barrel.

Because I have absolutely NO experience with this cartridge, and since I have no idea what your experience with QL is, I'd like to tell you how I use QL to stay out of trouble (with good success so far): I pretty much just look at the velocity corresponding to the highest pressure I'm willing to accept (in this case I'd probably choose to limit my loads to about 3125 +/- a few fps based on QL results). I would also look at all the other data available to see if the result appears to be plausible...for instance, I would not expect 7977 to yield 200 fps more than 7828.

Don't mean to appear to be talking down to anyone...I'm just not willing to assume anything at all.

Hope this is helpful!



Code
Cartridge          : 6.5 x 68
Bullet             : .264, 127, Barnes 'LRX'BT 30228
Useable Case Capaci: 77.098 grain H2O = 5.006 cm³
Cartridge O.A.L. L6: 3.405 inch = 86.49 mm
Barrel Length      : 24.0 inch = 609.6 mm
Powder             : IMR 7977 Enduron

Predicted data by increasing and decreasing the given charge,
incremented in steps of 0.185% of nominal charge.
CAUTION: Figures exceed maximum and minimum recommended loads !

Step    Fill. Charge   Vel.  Energy   Pmax   Pmuz  Prop.Burnt B_Time
 %       %    Grains   fps   ft.lbs    psi    psi      %        ms

-01.9   97    68.51   3051    2625   58516  13806     93.8    1.186  
-01.7   98    68.64   3057    2636   58874  13835     93.9    1.182  
-01.5   98    68.77   3063    2646   59235  13863     94.0    1.179  
-01.3   98    68.89   3070    2657   59597  13891     94.1    1.176  
-01.1   98    69.02   3076    2668   59963  13919     94.2    1.172  
-00.9   98    69.15   3082    2678   60330  13947     94.3    1.169  
-00.7   99    69.28   3088    2689   60700  13974     94.4    1.166  
-00.6   99    69.41   3094    2700   61072  14002     94.5    1.163  
-00.4   99    69.54   3100    2710   61446  14029     94.5    1.159  
-00.2   99    69.67   3106    2721   61823  14056     94.6    1.156  
+00.0   99    69.80   3112    2732   62203  14084     94.7    1.153  
+00.2   99    69.93   3119    2742   62584  14111     94.8    1.149  
+00.4  100    70.06   3125    2753   62969  14138     94.9    1.146  
+00.6  100    70.19   3131    2764   63355  14164     95.0    1.143  
+00.7  100    70.32   3137    2775   63745  14191     95.0    1.140  
+00.9  100    70.45   3143    2786   64136  14217     95.1    1.136  


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I just checked the 103% calculation against this and it is in the ball park of the QL data. I would still proceed cautiously and adjust the case capacity for your loads as I saw up to three grains difference from various sources. The default volume was high on QL.


"When you disarm the people, you commence to offend them and show that you distrust them either through cowardice or lack of confidence, and both of these opinions generate hatred." Niccolo Machiavelli

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