Monday, January 24, 2011

Casting Breakthrough with the 145-SWC. Effective on other moulds as well.

Smaller than expected bullet diameters of the 145 mould are affecting accuracy. Testing has shown that fullsized 360 bullets are best. 

The seam diameter ranges from .3591-.3594 in.  Across the seam typically ranges from .3584 to .3589. That is not good for achieving the best groups possible. 

First, the bottom line results.  The diameters now, after running a series of tests. measure .3598 to .3601 on the seam and .3593 to .3595 across the seam.  That's as dropped from the mould, before any aging grows or expands them.  (The effect of aging is the subject up an upcoming post.)

The final results are yet to be proven at the range, but that's coming soon.  So far the best groups have been 1.24 inches at 25 yards, with the undersized bullets.  From a rest of course, using my Red Dot Taurus 66, with a 6 inch barrel.

Lessons learned: Alloy temperature and mould temperature are absolutely critical. The alloy solution is easy, the Lee pot turned on full worked the best.  This is much hotter than most folks recommend, much.  Preheating the mould to 360 degrees also is critical.  The first cast will drop good bullets, then you must keep it from getting too hot.

First some data, then the process.  

The Lee pot is numbered 1 through 9, going all the way to what I'll call 9.5.  Casting at the different numbers, using the same one cavity and casting back to back, the diameters are in the chart. (click on it for a bigger view)

The numbers on the bottom are number of bullets cast in each test.  With more test bullets as the diameters increase.

The green line is the pot set to full hot, it's also is the one with the mould at 360 degrees.  This gives the maximum size, until the mould is too hot.  At that point size decreases, as you can see in the graph.

I ran a quick test and found that holding the mould on a wet rag for 5 seconds, than pausing for a couple of seconds, drops the temp 15-20 degrees.

Taking the lessons learned and putting together a test session produces the great results detailed above.  As a matter of fact a full casting session produced bullets even bigger.  All the way to .3601.  That's amazing.

The process that produces these fully sized bullets is repeatable and works on other moulds too.

The steps to follow are:

  1. Get the alloy fully up to temperature before starting to cast.  Set to 9.5 then don't start casting until the pot cycles off.  This takes much more time than usual
  2. Use a hotplate to get the mould to 360.  Use a basic kitchen thermometer with a flat bottom and stick it  into a middle cavity.
  3. If needed, use the alloy in the pot to add heat to the mould if needed, dip the mould into the hot alloy.  Use a damp rag to cool it if it's too hot.
  4. Start casting, (note: if one or two cavities vary in size, don't cast them.  Use the 3 or 4 most consistent and largest cavities. More on that in a future post as well.)
  5. For the first third of the pot, every three casts cool the mould by pressing it onto the damp rag for a 5 count, remove it from the rag and wait another 2 count
  6. Resume casting
  7. The bullets look shiny when dropped and then show some marking as they cool.  Watch closely and you learn to tell from their "look" if the mould is too hot or too cool
  8. After the first third pot it works best to cool the mould after 2 casts

That's it in a nutshell.  I suggest you do a similar set of tests and see how it works for you and your alloy.  Then refine the steps and the timing to work best for you.  

This test alloy is 98% lead and 2% solder, my preferred for all 357 magnum handgun bullets.

Next, the 145 bullets are aging for a week as part of another test.  The affects of the sizing/lube die, followed by the bullets enlarging will be documented in an upcoming post.  The range test is coming in the next few weeks.

Stay tuned and shoot well.

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