Odd issue with powder drops

[Perplexed]

I'm just starting out with reloading both cartridges and shotgun shells, and for the latter, I acquired a used Mec 9000 progressive loader. The other day I got it cleaned up, oiled and greased properly, adjusted according to the manual, and set up on my bench. I looked up load recipes for cowboy action shooting, and found one for 12 gauge that called for a maximum of 19.7 grains of Hodgdon Clays with 7/8 oz shot. I decided to download the powder charge by 15%, which was approximately 16.7 grains, and checked the Mec bushing chart for the appropriate sized bushing. That was No. 30, so I installed that in the charge bar, loaded the bottles with powder on left and shot on right, and tried a few powder drops to weigh them. I weighed an empty hull before the drop, and again afterward, to get the approximate weight of the powder.

I was mystified to find that ten powder drops resulted in an average weight of 17.3 grains with a range of 17.2 to 17.4 grains, not at all what I was aiming for. Scratching my head, I checked the bushing chart again, and realized that the actual weights were what was listed for the next up bushing, No. 31. So I swapped out the No. 30 bushing for the No. 29 bushing, and weighed another five powder drops.

They were all the same, 16.7 grains - what the chart said the next larger bushing should drop.

Has anyone run into this before?? I figure if it's consistent, I'll go with the No. 29 bushing despite what the Mec chart says, and just weigh every fifth or tenth drop "to make sure."

ETA: yes, I double-checked to make sure the correct bushing was installed the first time!

 

[Rod Snell]

Loaders tend to drop light if you just work the bar for the powder and don't go through the full cycle; the added vibration of the full cycle tends to settle the powder.

 

[rickm]

Also i have found it depends on the powder your using, to be accurate you have to use the same type of powder the company was using when they set the diameter of the bushing. What im meaning is if they used a fine grain powder and your using a courser grain it will measure out different and works the same in reverse.

 

[dennishoddy]

Make sure you're consistent when running the handle up and down, getting the same "impact" up and down. Make sure you hit the mechanical stops on the press with a tad bit of force, up and down.

 

[dennishoddy]

Also i have found it depends on the powder your using, to be accurate you have to use the same type of powder the company was using when they set the diameter of the bushing. What im meaning is if they used a fine grain powder and your using a courser grain it will measure out different and works the same in reverse.

Correct, ball power meters differently that flake powder. Good observation!

 

[Perplexed]

I do make sure I cycle the handle fully - being that I'm new to reloading, I'm a bit OCD about making SURE I go through the motions properly. I don't know how you folks can think reloading is relaxing - I would have the ceiling fan going since it's SO warm in the room, if it wouldn't mess up the reloading process.

So it's just plain coincidence the one bushing is dropping right about the same amount of powder that's listed for the next larger bushing?

 

[358norma]

Mec powder bushing are a close guess as to how much powder they drop per the "chart". You have done exactly what you need to do with them, measuring the amount of powder the one you have vs. what you are trying to drop. Over time you will acquire an assortment of powder bushings if you make different loads. Good job checking before you started loading.