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Help with 300 RUM velocity standard deviation

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Unread 08-12-2011, 12:20 PM
Bronze Member
Join Date: Feb 2011
Posts: 78
Help with 300 RUM velocity standard deviation

I am new to reloading and have just finished my first batch of test loads. I am shooting the following:

300 RUM Sendero
180 Grain Accubond
Retumbo Powder
Federal Gold Medal 215M primers
Federal Brass

I tested 5 different loads, the same COAL but i varied the powder charge by 1 grain with each load. I started with 95 grains of Retumbo and then 96, 97, 98, 99 grains. The load at 99 grains was by far the most accurate. Center to Center the 99 grain group was .244". The 5 shot group had the following velocities, in the order that they were shot, 3401, 3375, 3401, 3367, 3367. This is a total deviation of 34 fps.

Can anyone comment If this is a good deviation or if it is too large? If it is too large spread, what can i do to make the spread less.

Just so you know, at this charge the primer showed some very slight signs of high pressure, the primer had just barely begun to flatten. Also, the groups I shot were at 100 yards.

Thanks for your help.

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Unread 08-12-2011, 12:32 PM
Silver Member
Join Date: Jan 2010
Location: AZ
Posts: 306
Re: Help with 300 RUM velocity standard deviation

34fps isn't bad at all. It is possible to get below 20fps, on a rare occasion single digits. I dont trust my Chrono to be that accurate to be measuring a .3% difference between a string of 3 or 5 shots. In my experience I don't think you will get a lot lower extreme spread with Retumbo. From what I've found, H1000 gives up a little velocity to Retumbo, but has a lower extreme spread. My 208 Amax in 300RUM have an extreme spread in the low teens most of the time, one one occasion in was near 40fps for 5 shots. You might try H1000, but if it were me, I would stick with what you have. You may find 34fps to be your best or worst in your next few outings.
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Unread 08-12-2011, 12:39 PM
Bronze Member
Join Date: Feb 2011
Posts: 78
Re: Help with 300 RUM velocity standard deviation

Thanks for the feedback...I will load a few more up and make sure I am super precise when it comes to measuring powder (I was last time also) but it doesn't hurt to make sure.

Maybe it's best to get a 300 yard group or two and that should tell me if my velocities are too far off as well?

Again, I appreciate all the help!
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