Using the CAD function for spool shaped bullets

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Joined: Tue May 27, 2008 7:31 am

Using the CAD function for spool shaped bullets

Post by Pinzgauer » Tue May 27, 2008 8:05 am

Dear Dan;

I am a new user/customer so there is little doubt that some of my issues would be resolved with patience and practice...thanks for the opportunity to ask questions in this way. I did not see any other posts addressing this issue…

The bullet is to be pure lead or 2% tin alloy for low velocity (700 - 950 fps) use in an air rifle. Since air rifles do not use cartridges there is no need for a crimping groove. The caliber might be.308 or .338 and about 100 - 150 grains if .308 or 175 – 200 grains if .338.

Since bore friction, swaging the bands into the rifling and obturation are the major impediments to getting the bullet down the barrel and up to speed, I have reasoned that a bullet with minimal bore contact area might be a good idea for the low energy game I want to play.

A bullet with the shape of a sewing thread spool came to mind, a long body/groove separating narrow bands far forward and back, perhaps with a short wadcutter nose or a tangential ogive. It looks like your software demands a minimum meplat diameter.

Now my question is this: when I vary the bullet weight, nose shape or band, groove and bullet length dimensions I get aberrant lines on the display. Sometimes the ogive comes to a point with an inverted triangle sitting atop it.

How do I know when I have arrived at a tenable design, something you can actually make?

Another way of asking the question is "how do I know when I have asked the CAD function to draw something that is physically impossible?"

Kindest regards,

Mike B

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Re: Using the CAD function for spool shaped bullets

Post by mtngun » Tue May 27, 2008 7:39 pm

Good questions.

Yes, there is definitely a minimum meplat.

If the bullet drawing is going crazy, that's a pretty good indication that the numbers are not adding up. The most likely culprits are an excessively short nose, or not enough weight.

Other warning signs:

-- pop up warnings advising you to make specific changes

-- something other than "good choice" in the "recommendation" text box.

In theory, if the program allows you to place the design in your shopping cart, then the design can be cut. However, there are still a few exceptions to the rule. For example, it is currently possible to select a nose length shorter than the front band length and place it in the shopping cart.

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