Extrapolating a Pistol Load

[robertvarner]

I am working up a new 9mm load for some 147gr copper-plated bullets using CFE-Pistol. I would rather use my Lee Disk Powder Measure since it produces more consistent loads and it is easier to set up from the beginning of a session.

I need some help validating my calculations from the load data in my Lee Reloading Handbook (see attached photo).



I want to load with 4.2gr of CFE-Pistol, but the handbook does not show which Disk Number I can use (I know the handbook for some reason says to use the Lee Drum Powder Measure (LDPM), but I'd rather not) so I made the following calculations. Per the chart for 3.7gr of CFE-Pistol, you would use the 0.28cc Disk.

By extrapolating the new Disk value from the ratio of the difference between the two values of 3.7 and 4.2 of 0.5gr and adding it to the 0.28cc Disk, I get [(0.5/3.7)+0.28] = 0.41. By my calculations, I could safely use the 0.40 Disk.

Am I correctly extrapolating this data to utilize a larger Lee Disk to dispense 4.2gr? Answering this question will avoid "blowing my face off", or at least having a "powder shower" all over my reloading bench.

Thanks.

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[edzz]

Do you use a scale to verify the charge your lee powder measure is throwing?

 

[No_Regerts]

It finally happened. I need some of that math I sat through in school and I can't remember a lick of it.

 

[nammac]

So, my personal experience with the Lee disk powder measure is the published cavity capacities do not match what they actually throw, measuring with a digital, calibrated, scale. I've found them to be lighter than published. Loading without a scale for charge validation is, in my personal opinion, playing Russian roulette all by yourself...

Now, having said all that, you should be able to get the charge table for the disk measure from the Lee website. But I highly recommend getting a scale, just to be on the safe side.

 

[gmerkt]

Math isn't my strong discipline. But something seems wrong with the math here. You're talking about two different disc sizes, one .28 and another .40. The difference in volume is 42% increase as I get it.

The powder, on the other hand, 3.7 gr. and 4.2 gr., that's only a difference of 13.5%. So if you use the .40 disc you are going to get a charge increase of 42%, way more than half a grain. You'd be up to something like 5.25 gr., way over-charged.

If you want an increase of 13.5%, you'd want a volume increase of .0378 cc, or total .3178, or rounded up, .32.

You don't have to know math too well to see this. The difference between .28 and .40 is simply greater than the difference between 3.7 and 4.2. Not right?

Another thing. I don't trust CFE Pistol in max loads, much. Going by Hodgdon's online data, I used a load right in the middle of their suggested charge range that turned out to be pretty hot. Just my experience.

One last thing. I have an RCBS Little Dandy measure. On several occasions, I've found it to be inaccurate per their chart. I don't know that I trust pre-measured volume loading all that much.

 

[Zathras]

I'll second some others on trust-but-verify... I highly recommend an Ol' School scale (I like my RCBS M500). It needs no batteries - just verify 0 routinely and you should have no problems. Regardless of how consistent your powder measure's throw seems to be once dialed in, any adjustments should be verified again, with preferably 5 (some people go with 10) throw-measure cycles before anything gets dropped into a case. Good luck and safe loading...

 

[Xaevian]

Stop. Your math is wrong. You need to find the cc to grain ratio, not a proportionate increase. You are better off looking up the Volume Measure Density (VMD) for that powder. CFE Pistol is .0754 cc per grain. Multiply that by your desired grains to get the corresponding volume measure. Use the disk that matches without going over. And as everyone else said, verify with a scale.

Lee's VMD chart is here.

 

[Caveman Jim]

When I first started loading pistol cartridges with my Lee turret I read about what disc to use for whatever powder & weight with the auto disc.
What I found out was that not all were accurate enough so I sought out a few "Gurus" here and they turned me onto a method that made loads with the discs more accurate.
It involves drilling a hole in the disc and threading a fine thread screw to protrude into the cavity for reducing the volume. I'll get a pic in the am.

 

[Xaevian]

That sounds like a good way to fine tune a "closest fit" system.

 

[robertvarner]

Do you use a scale to verify the charge your lee powder measure is throwing?

Yes, I do.

 

[Papercidal]

When I used a auto disc I found the charts to be almost useless other than as a starting point . Find a disc that is supposed to get close to your desired charge weight and just progressively move up in cavity size till you get the closest to your desired charge.

The auto disc is not a bad powder measure but it's limitation is that you either have to compromise by using a disc that is close enough to your target weight or modify the disc to drop a bit more. The auto drum is supposed to be a much better powder measure and is not very expensive.

 

[robertvarner]

I've had issues with consistency load-to-loaf with the drum powder measure and I don't want to use an RCBS powder measure because you are in effect using a single-stage press process.

Have you ever looked at something someone posted on a blog and then we're astonished to find out it was you who wrote it? Well, in my previous math calculations I neglected to consider the VMD of the powder. Doh!

I appreciate Xaevian pointing out my math error.

One of the issues with posting on a web site is you risk showing your mistakes, but I do appreciate those of you who responded to help me keep my face intact!

 

[Caveman Jim]

Here is what I was trying to explain late last night. I'll let the pics do the talking.

Thanks to @Dyjital and @ageingstudent for your insight and guidance.

 

[Xaevian]

I've had issues with consistency load-to-loaf with the drum powder measure and I don't want to use an RCBS powder measure because you are in effect using a single-stage press process.

Have you ever looked at something someone posted on a blog and then we're astonished to find out it was you who wrote it? Well, in my previous math calculations I neglected to consider the VMD of the powder. Doh!

I appreciate Xaevian pointing out my math error.

One of the issues with posting on a web site is you risk showing your mistakes, but I do appreciate those of you who responded to help me keep my face intact!

Your safety was my primary concern, sir.

 

[gmerkt]

If you want an increase of 13.5%, you'd want a volume increase of .0378 cc, or total .3178, or rounded up, .32.

CFE Pistol is .0754 cc per grain

.0754 x 4.2 = .31668

Two pretty close estimates. Volume is volume. But my preference is going by weight.

 

[Member 5605]

Here is what I was trying to explain late last night. I'll let the pics do the talking.

Thanks to @Dyjital and @ageingstudent for your insight and guidance.

View attachment 616979



View attachment 616980

View attachment 616981

One can also get for $9-11 the adjustable charge bars if you aren't as handy like Jim. Same solution, different routes.





And to contribute to the thread:

Lee will always load light.
The internal volume is based on hard plastic and the densities of the powder are calculated on absence of air in said volume.

Air = 0 weight so yes. They weight light.
The adjustable chargebar I have on every die head I own because it's way easier to dial in for pistol.

I ALWAYS drop 10 charges and weigh them you MUST take into consideration the rotating turret if you have one or the back and forth action of the powder drop to settle the powder between throws.

Same motion every time gives good consistent results. My favorite powders drop smooth and are very consistent with what I load in pistol. .1gr. variance on either side of the target.

Mine work well because I know how they operate.

 

[Caveman Jim]

I couldn't find my adjustable charge bar for a pic so forgot about posting it.

 

[robertvarner]

That's okay. I have one too from Lee, but it appears to not work over 1.2gr and doesn't stack properly on another disk (I have the side panels for the double disk kit), so there are some limitations.

I may have time this afternoon to do a test load (using proper reloader-math) and weigh it on my scale.

 

[Caveman Jim]

That's okay. I have one too from Lee, but it appears to not work over 1.2gr and doesn't stack properly on another disk (I have the side panels for the double disk kit), so there are some limitations.

I may have time this afternoon to do a test load (using proper reloader-math) and weigh it on my scale.

I found nothing in the instructions stating it does not work over 1.2g.
An example of 5.7g of Hercules Bullseye is attainable at .61cc setting.

Now I'm curious...

 

[robertvarner]

My mistake, it's 1.2cc, not grains.