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Author Topic: Loading by Density (Part 1)  (Read 177 times)

Offline Dutch-Hunter

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Loading by Density (Part 1)
« on: August 22, 2019, 05:42:36 AM »
Loading by Density (Part 1) Load Density Explained and Defined

I know some of you are already going… Good grief here goes Dutch again. Just hear me out. Even Gut may learn sumpin’.  @--0--0102

Tools required Digital Calipers, Over All Length Gauge, two sets of Comparators and a Digital Scale.

The load density formula has provided excellent results for many years. The main reason is simply that the load density formula works without fail. Eighty-five percent load densities is an ideal starting point, but let’s look at how reloaders have come to that number.

Density is simply the ratio of the cartridge case capacity and the actual amount of the case filled by powder. Pulling and checking some of our more accurate factory ammunition will show a density of 80 to 90 percent, so I am on the right track.

I do not like to use compressed charges. While I have done so, I can say the results have not always been good. A load of 100 percent density or greater is a “compressed loads”. Compressed loads are unpredictable to say the least, because there must be room for the ignition starting sequence from the primer to move across the powder charge. A compressed load retards this action. A compressed charge also leads to excess heat and barrel wear.

A powder charge weight that is low in density can cause a phenomenon called detonation. Detonation is a very rapid tremendous pressure spike and should be avoided. Too much air space is the culprit of detonation, which has been known to occur even in revolver cartridges. The sign of detonation usually is neck “ringing”. This is a bulging ring around the neck of the case. In bottleneck rifle cartridges this can also cause a bullet to “run out of gas” in the barrel and get stuck.

Calculating load density is relatively simple, but you have to know the cartridge case capacity first. There are various methods of figuring cartridge case capacity, but many are flawed. I do not think measuring capacity by filling an empty case is accurate enough. So here’s the “Dutch” way. I just called it this; I’m sure other people do it this way too.

First you must know your chambers Bolt Face to Land (BFTL) dimension. I use a Hornady OAL gauge and comparator.  Then I make dummy round (no primer) which is a case neck sized and trimmed to length, with the bullet I intend to use properly seated five thousandths short of the BFTL dimension and weigh it. (I always start my load development at a jump space of five thousandths.) This will give me my “dry” cartridge weight.  Next, I fill the case with water through and to the flashole using syringe and needle to a level just to the flashole, not filling the primer pocket. I weigh the case when filled with water, after scotch taping the base closed. This is now my “wet” or gross cartridge weight.

To determine the capacity of this cartridge you subtract the “dry” weight from the “wet” weight. Let’s say that the water capacity was 50 grains. A 40 grain powder charge would represent an 80 percent capacity of the case. Therefore, the powder charge would represent 80 percent loading density. It is seldom this cut and dry or this easy because of varying powder densities, but this is an easily comprehended example of how powder capacity is measured. Now I’ll explain why different powders behave differently. Simply stated powders have density variances because of their shape and chemical composition. I’ll dip deeper into this in Part 2. (Yes pun intended)

Q; What exactly is powder density? A; The density of a powder is how much a cc of powder weighs compared to that of water. Gun powder is less dense and densities vary among powders. The reduction in density of powders is caused primarily by the air that is contained within and/or around each sphere, flake or extruded cylinder of a given powder. Flake powders are the densest followed by spherical and finally cylindrical. Flakes lay together in a closer pattern thus making them most dense. Cylindrical powders are hollow and therefore have built in air space plus their shape like spherical powders which prevents them arranging themselves as tightly together as flakes. 

Q; Why do different powders have different burn rates? A: The chemical composition combined with their density factor determines the rate that a powder will burn or gasifies. Fortunately for all of us there is an easy to find “burn rate” table. Also available although not a readily available is a powder density chart. It is relatively easy to compute density factor of any powder.

Once you have searched the loading manuals, you can narrow the choice down to several promising powders.  Again, I don’t recommend running loads wide open for most starting situations. There are differences in performance in cold or hot weather as well as changes in elevation. A load skirting on the edge just may not be completely safe in all environmental situations. This is why you start out “safely slow” and gradually increase your charge weights. Yes I said “safely slow” remember we talked about “detonation” phenomenon. It is very real and can be as dangerous as a load that is too hot.

Recapping Part 1) this method of reloading in my opinion is the most uniformly accurate method of developing and loading cartridges. The most important measurement you must find is the chambers BFTL length which is the cartridges case base to ogive (CBTO). Remember my load development jump space is 5 thousandths. After you get a “good” load developed you can play with the jump later to find the “best” load with that gun with that powder with that bullet with that case with that primer. WOW! That’s a whole lot of “with that’s”! Dutch OUT!

If you'd like a PDF of this reply I can attache one or email it to you.

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TO old to care!

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Loading by Density (Part 1)
« on: August 22, 2019, 05:42:36 AM »
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Offline Gutshot

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Re: Loading by Density (Part 1)
« Reply #1 on: August 22, 2019, 07:09:31 AM »
Slow learner here, but I'm paying attention!!  @--0--0118
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Re: Loading by Density (Part 1)
« Reply #2 on: August 22, 2019, 10:35:10 AM »
Some very interesting info Dutch thanks.
If it's brown it's down

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Offline BoBallistic

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Re: Loading by Density (Part 1)
« Reply #3 on: August 26, 2019, 05:56:38 AM »
This weekend was our hot and humid and sweaty Work Weekend! With a crowd gather round, at dinner one night, I was asked the question about load density. I try to explain that how and why load density matters, (like every thing else if you relaod). I have told most guys if my load density for many years is between 83 and 88%. I did not explain it like Dutch Does in his eloquently style and manner, but most got the point i was trying to make....

Thanks Dutch for the lesson - Again.....

This weekend between the tractor and breakdowns and ATV wrecks we got finish around 4 PM and then it rain real hard starting around 6 PM...Perfect timing!! Maybe their is a sliver lining in those dark clouds....boy I am tired today!! it will take me a few days to get over the trip....going to the range this Wednesday....taking the smoke poles and a few other favorites.....Bo

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