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Old June 21, 2011, 01:12 PM   #5
Unclenick
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Join Date: March 4, 2005
Location: Ohio
Posts: 10,206
That's what drop tubes are for. They pack the powder tighter in advance of seating the bullet, so you can get more powder in. The exact mechanism would be interesting to study in detail, but I believe that by letting the powder pick up some speed on its way into the case, grans bounce and get more random opportunities to wedge into a close places that trap them from further bouncing.

The taller the tube, the tighter it packs. Black powder users have used drop tubes for this since the 19th century. There is often no other convenient way to pack 70 grains into a .45-70 under the long bullets.

In any event, some loads that have low enough bulk density would be compressed if left at that bulk density by shallow pouring, but with a long enough drop tube will pack tightly enough to stay below the bullet. I should probably make up and example and post a photo. I'll edit this post later to do show that.

A shaker table will do some added packing. Indeed, simply moving cartridges around tends to pack powder some to. I read mention by someone, I think maybe in Precision Shooting, who had a load that did fine at the range when he loaded at home, but when he put the same load together at the range it created overpressure signs and a sticky bolt. The vibration of transport packed the powder enough to slow its effective burn rate a bit by leaving less room between the grains for the hot gas and flame to propagate through.

Edit:

You can see how, for a flat base 125 grain or 150 grain bullet, this could take the load from compressed to packed but not compressed.



Note that this works best with stick powder. Hard sphericals show almost no change with drop tubes. I think that's one reason they meter so consistently whether you have powder baffles in your powder measure or not. But any powder that can pack will exhibit some of this effect with the drop tubes.
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Last edited by Unclenick; June 21, 2011 at 02:42 PM.
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