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powder charge vs velocity

 
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  #15  
Old 05-23-2012, 08:04 AM
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Re: powder charge vs velocity

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Originally Posted by BML View Post
That's the question I would like to know that answer to! They certainly were not compressed loads. I did a lot of testing with charges in the 48-48.5 grain range and never experienced any big variances in velocity like this.

Once the wind dies down up here I am going to test that same 50.5g and 51.0g again and see if I come up with the same results.
Let's say you shoot 30 of each load.
And, you alternate shots 50.5, 51, 50.5, 51, 50.5, 51... evenly distributing the effects of lighting, temperature, and fouling until you've shot all 60.

You collect each individual MV and calculate the mean and standard deviation for each load.

If the mean for each load is not separated by more than 2x the standard deviation, then you don't have much of a statistical confidence level to ascert that the mean will likely be different with future samples.

That's over-simplified, but the point is that small samples may hint at something interesting. But, it's no reason to question established principles.

You also don't have to shoot such large samples to work towards a good load. ...only to prove that the load will be consistent going forward. ...or, to statistically demonstrate some other extraordinary claim.

Either way, you've got a decent load workup started and will want to pick the best one so far and work on your seating depth before you burn out your barrel.

Good luck!
-- richard
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  #16  
Old 05-23-2012, 05:54 PM
BML BML is offline
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Re: powder charge vs velocity

Thanks again Richard! I appreciate the advice.
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  #17  
Old 05-23-2012, 06:29 PM
BML BML is offline
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Re: powder charge vs velocity

Thought I would share a few pics of the groups referenced in this thread.

50.0g--Average speed 2985--Group size .766
Ignore that top shot. That one was not part of the load tested here.



50.5g--Average speed 3039--Group size .799



51.0--Average speed 2861--Group size .358




Obviously, I am very happy with the 51.0g load and the first thing I will do is load some more and test again to see if I can repeat those results. I am struggling with a little internal dilemma though. I can't help but shake that something is "wrong" because of the drop in velocity. I guess as I see it now I have 2 directions to test. First try to duplicate 51.0g results. 2nd, play with seating depths on the 50.5g load and try to shrink that group as much as I can.

Again for all those that helped, I appreciate it.
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  #18  
Old 05-23-2012, 07:08 PM
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Re: powder charge vs velocity

This particular instance does raise flags of something going wrong with the chronograph because of the amount of declining velocity. I'd guess changing light conditions affecting the chronograph. More testing will tell you what's actually happening.

I've seen it many times that if you map your velocities with a particular powder combination, you can see a steady rise in velocity with powder increase, usually linear. As you start reaching the maximum powder charge the velocity per powder increment begins to decrease until you reach the point of diminishing returns and the velocity begins to decline as you exceed the maximum charge. Some combinations show pressure signs before the point is reached, and some combinations show a distinct velocity curve slightly before or right along with traditional pressure signs.
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  #19  
Old 05-23-2012, 07:24 PM
BML BML is offline
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Re: powder charge vs velocity

Brentc,

I actually did test with a chrono throughout. All of my prior testing was from 48-49 grains though. Speeds steadily increased with each load, but the closer I got to 49g the more my bullets just sprayed all over so I never tested above that. I'm new to reloading and just assumed my rifle wouldn't shoot anything well above that. I ask a ton of questions on this site and a member suggested I jump up and test 50.0g and up. This is the first round of testing with charges above 50.0 grains. The pressure signs I've seen have been only very slight extractor marks on the head. They are almost unnoticeable but they are there.
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  #20  
Old 05-23-2012, 08:08 PM
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Re: powder charge vs velocity

Quote:
Originally Posted by BML View Post
Brentc,

I actually did test with a chrono throughout. All of my prior testing was from 48-49 grains though. Speeds steadily increased with each load, but the closer I got to 49g the more my bullets just sprayed all over so I never tested above that. I'm new to reloading and just assumed my rifle wouldn't shoot anything well above that. I ask a ton of questions on this site and a member suggested I jump up and test 50.0g and up. This is the first round of testing with charges above 50.0 grains. The pressure signs I've seen have been only very slight extractor marks on the head. They are almost unnoticeable but they are there.
Based on all the indicators you've given, you're at the max for your load. What are the corresponding ES numbers with each powder charge?

If it were me making a decision based on what you've provided, I'd do a seating depth test at 50.0 grains. Once you find the sweet spot for seating depth, you can bump your powder charge up or down in small increments to find your best powder charge.
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  #21  
Old 05-23-2012, 08:25 PM
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Re: powder charge vs velocity

Sounds as though you may want to alter your powder choice, as you are altering burn rate as you add fuel to the fire. This is rather common with ball type powders, and with medium cases (the '06 clan) I've actually been able to use more of a given powder with a heavier bullet of similar construction because the heavier load had slowed the powder down. I've also been able to push past medium charges that were seemingly topped out and get a good bit more out of the load. With stick powder, it is a sign that you are topped out and any more powder will just make the rifle work harder for the same result.
I'm curious as to why you are only using 1/2 grain increments on a caliber that is able to burn 50 grains.
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