Micro Band Bullet missing Micro Bands

 Lee Micro Band Bullets

 Disappearing Micro Bands


Lee Precision Inc. developed the new bullet design variously called tumble lube bullets or micro band bullets, and occasionally micro groove bullets.

Lee's description from their catalog states:

Micro Band Bullets usually require no sizing. A great innovation possible only because of Lee Liquid Alox Lubricant. The bullet shank has many shallow grooves for maximum lubricant retention. They all have a bevel base just behind a solid driving band. A great way to make bullets in quantity with minimum time, effort and equipment. More accurate than ordinary cast bullets.

The subject of this page is the  Lee TL358-158-SWC but the effect occurs with all micro band bullets.

The effect is caused by the bullet being cast significantly over sized and then when run through the sizing die, the bullet is swaged down so much that the bands are eliminated. Since the swaging operation in the sizing die doesn't remove any metal, where did the bands go? The answer is that it went into length. Before sizing this bullet measured 0.663" in length. After sizing, it measured 0.674". This bullet, when cast correctly from the same pot of alloy, weights 158.5gr. This over sized bullet weighed 165.8gr.

Several things can cause the mold to drop oversized bullets:

  1. Misalignment of the alignment pins, or pins and groves in the case of a two cavity mold.
  2. Sprue plate binding and retarding the closing of the blocks.
  3. A splash of lead on the face of one of the blocks.
  4. A burr or scratch on the face of one of the blocks.
  5. A warped block.
  6. Damaged or misaligned handles.
  7. Too much smoking or mold release on the face of the blocks.
  8. Pressure on the sprue cutoff lever on the six cavity mold.


Most of the cases I have heard of where this problem occurred were with bullets cast with the Lee six cavity mold. This mold is a very nice design. It has a lever used to cut off the sprue with no need to strike the sprue plate. This lever is very powerful. It has a mechanical advantage of 5 3/4" : 5/8"  = 9. This means if you apply a pound of force to the end of the wooden lever handle, it applies nine pounds of force to the sprue plate. That may not sound like a lot but this is half as much mechanical advantage as several O frame reloading presses. 


Photo instructions:  Expand images with the control key plus the mouse wheel or maximize them by click on them. They will open in a new window at the maximum resolution. Control + Wheel Forward zooms in. Control + Wheel back zooms out.



Before and After

Before and after photos of the same bullet, before and after sizing. Note that it is obvious that the unsized bullet has problems. It is visually too large with metal extruding into the seam.

This bullet was chosen to exaggerate the wiping action on the micro bands during the sizing operation. And, because it turned out to be the absolute maximum diameter I could push through the Lee .357 sizing die.

This bullet measured an average of .376 before sizing. Obviously it was not round. The measurements varied from .374 to .379.

In addition to reducing the diameter, the swaging action of the resizing die increased the length of the bullet from 0.663" to 0.674"




Some users new to these molds grasp all three handles to hold the mold closed. This method is incorrect and will ( not may ) lead to problems with bullet diameter. This was the method used to produce the bullets for these photos.


It takes very little pressure on the sprue cutter lever to open the mold blocks a crack. This photo shows the user grasping the lever with the entire hand. Experimentation to see how much pressure was required showed that simply wrapping the little finger around the lever handle and grasping it lightly with only the little finger would cause the front of the mold blocks to open by 0.011"


Lee Mold Incorrect Grip

This is the correct way to hold the Lee six cavity mold while pouring the bullets. Notice that in the above photo, the sprue handle is touching the mold handle on the right side. Actually the middle handle in the photo. This is not a result of squeezing the handles tightly. It takes surprisingly little effort to do this

  Lee Mold Incorrect Grip


This photo shows a close up of the mold blocks tightly closed. Please expand the photo and take a close look at how tightly the blocks fit together.


This photo shows a close up of the mold blocks being held open by slight pressure on the sprue lever. Please expand the photo and take a close look at what pressure on the sprue lever can do to the tight fit of the "closed" mold blocks.
























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