Math question for progressive reloaders..


January 1, 2006, 12:08 AM
My questions pertains to the volume of a cylinder. Specifically, the 'cylinder' in question is a powder dispensing slide for a progressive reloader.

The volume of the slide is 4. I want to increase that value by 25% to 5.

The depth ( or height ) is non adjustable.

My only option is to increase the diameter.

I don't have math keys on the keyboard so I will need to use words rather than symbols.

If the existing diameter is known and designated as D sub-1, and the desired diameter is designated as D sub-2, then I THINK the formula for increasing the volume of the slide by 25% would be expressed as:

D sub-2= square root of (1.25 X D sub 1 squared)

The existing powder slide charge bar dispenses 4.0 grains of Bullseye. I want to increase the volume to load 5.0 grains.

What is the formula for increasing a known volume of a cylinder by 25% by only changing the diameter?



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January 1, 2006, 02:15 AM
Your math is correct,--
D2 = D1 x sqrt(1.25)
D2 = D1 x 1.118

If you simplify your
D sub-2= square root of (1.25 X D sub 1 squared)
D sub-2= (square root of 1.25) X D sub 1
then your expression is the same as my rendition.

However, it might be prudent to do an intermediate step, to increase the diameter by a factor of about 1.05-1.07, and test it. Futzing around with Bullseye can be a bit tricky.

January 3, 2006, 12:29 PM
Thank you sir...

What is going on here is that I have a Star reloader that I haven't used in a couple of decades or so...The Star was, and is, a good machine. Its just not exactly versatile.

Powder versatility is acheived by changing powder slides and they are no longer made.

Instead of using my existing slides of 2.7, 3.5, 3.8, 4.0 of Bullseye, I want the machine to throw 5.0 Bullseye. How to use the existing 4.0 slide to change to 5.0 would be considerably simpler for my remaining brain cells. Thank you for you conformation of the math. I will proceed cautiously.

Now all I gotta do is figure out how much to change the 2.7 Bullseye charge bar to dispense 6.5 of the 'new' Unique.

Thanx again,


January 3, 2006, 04:20 PM

You DID verify that the "4.0" slide actually throws an average of 4.0 +/- 5% or less, right?

I recommend throwing 10 charges and weighing them, at least two sets. That'll give a good average.

January 3, 2006, 04:59 PM
Hello Grump,

Yes I did kinda/sorta verify the 4.0 slide but it was a couple or three decades ago. Nothing has changed except that I must have lost a few billion brain memory cells since then.


January 4, 2006, 08:09 PM
You might want to check the throw weights again with current powders. I recently found that Accurate changed their #2 powder - same energy/grain, so loading data remained the same, but the new powder is bulkier so larger cavities are needed to throw the same weight as before. If your data really is decades old you ought to check with currently available product (unless you're using 30 year old powder too, in which case . . . I'd still check it. ;) )

January 4, 2006, 11:25 PM
Make sure you "sneak" up to it. You want a specific "weight" in a powder charge but you have to set a "volume" to get a specific weight with the measure. a 25% increase in volume may not give a 25% increase in weight.

January 5, 2006, 04:18 AM
Math aside, how are you going to increase the calibre of the tube to give exactly 5 grains? What cartridge are you loading? Just curious.

January 6, 2006, 11:16 AM
Hello Sunray,

Sorry if I was a bit vauge. The 'tube' is a powder slide for the now out of print Star Progrssive reloader. I intend to load 45 ACP with the 200 grain Hensley and Gibbs profile bullet and 5 grains of Bullseye.

If I know that a given diameter throws 4.0 grains of powder, and I can determine how much to increase that diameter to dispense 25% more powder, enlarging the diameter of the brass powder slide to that measurement shouldn't be much of a problem.

I 'spect I'll determine the desired diameter, find a drill bit of slightly less than that diameter, and, using a drill press, enlarge the diameter of the powder slide.

Then I'll check it out..throw a bunch of powder charges, get the average weight, and adjust if needed.

Do you have any other suggestions?



January 7, 2006, 08:18 AM
Lee lists one grain of bullseye at .1064cc. So 5 grains would equal (5x.1064) .532cc (.53 from the Lee volumetric table). 6 grains is (6x.1064) .638cc

So, in a perfect world, a hole that had a volume equal to .53cc's is what you are after.

Will it throw 5gr every charge? No. Bullseye is a flake powder, so depending on how the flakes lay in the cylinder, you could see a smaller weight per throw (ball powders are the most accurate, all other powders will vary proportionally to the length of the grain).

If your press takes standard dies, you may want to simply buy a Lee Pro Auto Measure and the proper expander die. The Pro Auto measure (NOT the Perfect Powder measure) works on just about every press out there and for the $30 you'll spend on the measure and die has to be less than the time/material to ream out your exisisting charge tube.

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