More .40 S&W/Lee Auto-Disk powder measure questions

[gunrat]

Okay, I was going to test my first new reloads today at Guns & Leather. After going over what I did and the data I used with Mark Crabtree, he discovered that I had made a mistake in reading the data, and I decided to get a bullet puller and start over. Mark also recommended using different powder than I was using, so I bought some Alliant Unique powder.

So, I get to setting up the Lee Auto Disk and start checking charge weights on a digital scale. The Speer manual recommended a starting .40 S&W charge of 6.2 grains of Unique for the 165 grain jacketed bullet I am using. So, I looked in the Lee manual to find a disk setting that matched 6.2 grains of Unique, and the Lee Auto Disk Capacity chart on page 708 of the manual shows that for Unique, a .66 cc disc should throw 6.0 grains. The overall question is, has anyone here found the charges thrown by the Auto Disk to throw lighter than listed charges in the manual?

So I change disks up to a .71 cc, then a .76cc to finally arrive at thrown charges of 5.7-6.0 grains. This is a much different weight than the Lee manual says should be thrown with that disk for Unique, so I am going to await the advice of someone here before I give that bullet puller more exercise! Also, if 6.2 grains is the starting load, is 5.7-6.0 grains close enough for practice ammo and normal cycling of the battery?

The digital scale is brand new, and since each bullet weighed 165 grains on the scale, this doesn't seem to be part of the problem. I also checked the adjustment of the Powder-through Expanding die in case that could have been a factor.

As always, thanks for your help, and major public kudos to Mr. Crabtree for his advice and assistance in keeping me out of my own way!!

[Slasher]

I have the pro auto disks and have seen the same thing. I normally use the Lee documentation to get an idea on which disk to start with and then just go through a couple of them to see what kind of weight drops I get with each hole. Once I do this I record the weights for each hole for each powder and have it for future reference.

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[Jonnin]

The data provided for the auto disks is way off (is it really old or poorly done? Not sure), you have to weigh your powder for one of the disks to see how much it puts out (average of several goes). Once you weigh it one time, you can grab your calculator and determine what disk you need. For example, say you need 6.5 grains of the above for your next round. Then you take .76 / 6 = .12666, multiply .12666 by 6.5, and it comes out .823 so you grab the disk that is closest to .823. Sometimes, for some powder and bullet weights, its not easy to get the load you want and you may find that 2 hits of a smaller disk is better than your choice of too hot a load or too weak a load. The disks simply are not capable of every possible bullet weight/powder charge / caliber combination, but they cover most. Another way to handle it is to change powders to see if a different brand or burn speed will match to the disks better. You want to weigh the setup you select again, to make sure you are getting what you thought you would get, but this saves a LOT of swapping the disks and weighing a bunch of charges.

As for loads to cycle the action and practice, it depends on the gun. Some guns (glocks!) will not cycle starter loads and you have to increase the powder until the ammo works well. Other guns cycle great on less than starter loads of powder --- its largely tied to the recoil spring in the gun and weight of the slide. I usually just make about 10 rounds, test it, and if it works, go with it, if not, increase the charge say 1/4 the difference between starter and max load rounded down to the nearest auto disk.

[gunrat]

Thanks for the advice!