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  #1  
Old 10-25-2013, 10:22 AM
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When does load density?


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When does load density become a problem( less and more).Thanks in advance.



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Old 10-25-2013, 02:18 PM
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It sort of depends on the type of powder, the size of the particles, and how much you need to squeeze the stuff seating the bullet.

On the low end, you really need to know the powder well, as that is a complicated issue tat covers a lot of variables.

If you have a long extruded rod, like 4350, the powder is actually loosely packed when you drop the charge. There is lots of void space, and even 10% compression will not overly compact the charge. (Please do not run out and compress a load of 4350 in a 7mm Mag with a 175gr bullet).

If you are loading a small particle ball type powder, it settles more densely, and even 5% may be excessive.

Many variables.

Too much compression has a couple costs.

It can actually push a bullet back out of the case, especially without a crimp.
It can inhibit ignition, resulting in erratic velocity and accuracy.

I have a comfort level at about 100-105% load density. Past that I feel a faster powder is in line, or I need a "Short Cut" version.
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Old 10-26-2013, 04:43 AM
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Randy,

The two extremes are too much compression and so little powder that when it settles sideways in the case, the primer gets more surface area to ignite than normal, which can raise pressures.

QuickLOAD's default compression limit is 5%, and that's probably a good number to observe to avoid the overfilling problems T-man described. A general rule about the ignition overpressure issue is that if you stay above 70% load density you won't have it. This varies with the powder, though. H4895 is able to go rather lower, as can the faster IMR sticks, like IMR 3031. Hodgodn says you may use as little H4895 as 60% of maximum load. That might take you down around 50% fill in some instances. Plots done by Dr. Lloyd Brownell in the mid-60's didn't show pressure erratic events until 40% with 3031, IIRC. Perhaps H4895 can even go that low, but I haven't tried it. There is little reason to these days as the velocity variation is high with such low case fill, depending whether the powder falls forward or to the rear just before ignition. Trail Boss and other bulky powders like SR4759 are available for reduced loads without the fill falling off so badly.

Still other powders, like H110/296 for magnum revolvers want to stay above 85% or they can squib out. Still other very fast powders, like Bullseye, HP38/231, Red Dot, Clays, R1, N310, etcetera, are perfectly happy at 25% load density for light target loads. They burn so fast the ignition irregularity from the position of the charge in the case is a minor part of the curve.

Homer Powley's original slide rule calculator for rifle loads worked only between 85% to 100% fill. If rifle is what you are working with, that is a reliable performance range that won't cause any surprises.
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Old 10-26-2013, 08:09 PM
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I'm using some Ramshot Hunter in my 6.5-284 norma. 53 grs and it comes to the bottom of the neck.Thanks for the info.I can learn a lot on this forum.

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Old 10-27-2013, 05:59 AM
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If you're using a powder that requires you to compress it heavily in order to get the pressure/velocity you are looking for, consider going to a slightly faster or less bulky powder. While your load density can be quite low with some powders and 105% or more, with others, most prudent reloaders stick with a powder/charge that peaks out somewhere in the mid to high 90's, in terms of percentage of fill.
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Old 10-27-2013, 07:52 AM
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Quote:
Originally Posted by broom_jm View Post
If you're using a powder that requires you to compress it heavily in order to get the pressure/velocity you are looking for, consider going to a slightly faster or less bulky powder. While your load density can be quite low with some powders and 105% or more, with others, most prudent reloaders stick with a powder/charge that peaks out somewhere in the mid to high 90's, in terms of percentage of fill.
That is good advice if you feel you need that performance, but I would say perhaps you shouldn't be looking for the oressure and velocity you are looking for. If it is a modern high powered rifle cartridge, the chances are that an uncompressed load is enough.

Leaving safety out of it (as with 105% density and a good modern rifle and brass you possibly can, there is a chance of uneven compression, sometimes directly under the bullet, sometimes hear the head, at the edges or in the centre... Consistency can't be bad. If I really wanted more powder in, the first thing I would do is to see if a long drop tube would do it.
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Old 10-28-2013, 01:53 PM
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Quote:
Originally Posted by John Wallace View Post
Leaving safety out of it (as with 105% density and a good modern rifle and brass you possibly can, there is a chance of uneven compression.
Well John, seems you like this sort of thing

Compression in particle beds of uniform particle size and configuration, are subject to the Cauchy Elastic Formulation which describes the axial stress on the material, and the effect of the wall friction coefficient. For laterally confined compression, axial compression forms a gradient, and particle deformation forms a gradient dependent on the material modulus. This is subject to nonlinear kinematics.

Or squeeze the top, and a non-uniform gradient of particle density forms. Rate of formation and total compression are interdependent, and the variance is exponential with particle modulus.

Or, it's hard to squeeze powders very much, before predictable results get screwed.

I love physics,
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Old 10-28-2013, 04:14 PM
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Are those words even allowed on this board? I have never heard such language before!

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Old 10-29-2013, 10:44 AM
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Long Words on a Deep Subject.
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