Saturday, February 12, 2011

Final report on the changing bullet diameter, sized and unsized. How to use it to improve accuracy.

The soft alloy that is so accurate in a 357 magnum drops from the mould a little smaller than harder alloys.  Having the optimum alloy is more important than the optimum size, so the soft alloy is the best approach.  You can then use the changing size to squeeze the last bit of accuracy out of the bullet.  Read on:

The final measurements of this test are in the chart below.  The blue is not lubed, the green is a lubed bullet.  Note the sizer line at .360 inch.  That's the actual measurement that my Lyman 450 sizes at.  Check yours as they can be vary a bit:

Click on the graph for a full size readable view.

In case you haven't had a chance to read the prior post, the blue line is a bullet that was unsized/unlubed measured on the seam for 4 weeks.  The green line is a bullet from the same cavity, cast a few seconds later.  It dropped at the same exact size, as you would expect.   Shortly afterwards the second bullet was put through a Lyman 450 Lubrisizer.  The sizing .360 die (the highlighted line) didn't change the size at all since the bullet was smaller.  FYI, the lube is Darr Lube, which is my go-to homemade lube.

The results are striking.  The lubed bullet stayed close to the same size, expanding a little bit and then constant.  The unlubed bullet grew above the .360 size, which works best for accuracy and is very useful.  What's also useful is the fact that once lubed the bullets stay fairly even over time.

Recognize that not every bullet grows the exact same amount.  Also recognize that a bullet doesn't expand/grow the same amount evenly.  The ideal process to use this new information is:
  1. Cast the bullets
    1. The 50/1 lead/solder alloy likes 900-975 degrees
    2. It also likes the mould preheated to 400 and kept between that and 420 (cavity temps).  There will be more extensive cavity temp test results coming as even hotter mould temps may offer some advantage.
    3. This is considered too hot by many, it isn't for this alloy.  Also, if you do everything the same way as everyone else, how will your bullets be more accurate than theirs.  Try casting with this alloy and see the results
  2. Put them into a glass jar or someplace they are open to the air
  3. Wait two weeks
  4. Size and lube
    1. Having the bullets at maximum size will allow the bullet to expand around it's entire circumference as much as possible
    2. They will then keep their .360 optimum size, although this calls for a test to see how long they are constant
They are now ready to load and shoot.  These are the most accurate bullets you can cast and put in your revolver.  Check prior posts to see which moulds are the best.

By following these steps the bullets will be fully and evenly sized, and very round.  This provides the consistency needed for excellent accuracy.

If you are casting with harder alloys, see if you can get some stick-on wheel weights or plumbers lead.  Validate for yourself that 98% lead 2% solder will shoot more accurately in a 357 magnum than other alloys.  The Accuracy Ladder in a prior post highlights exactly what is most important to cast the most accurate bullets possible for your 357 magnum.

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