Twist rate bullet calculations ?

[ndt man]

Can any wise person answer the following
Using a twist rate calculator
If I put the bullet overall length in it comes out as marginally stable ( 1.455). If I put the same information in but add the ballistic tip length it tells me it's a very stable bullet
( 1.722) why two different. Calculations same bullet ??.

 

[NigelM]

Because the weight of the plastic tip is minimal so the calculator is reducing the effective length of the bullet thereby making it more stable.

 

[ndt man]

Thanks for the reply

Because the weight of the plastic tip is minimal so the calculator is reducing the effective length of the bullet thereby making it more stable.

Thanks for that ( I'm using jbm) some others don't give the option to add tip length. So I wonder how this affects there calculations.?

 

[NoIDeer]

Been using a Lee loader for a few years now, no crimp and no problems. As others say if it ain't bust...

 

[NigelM]

Thanks for the reply

Thanks for that ( I'm using jbm) some others don't give the option to add tip length. So I wonder how this affects there calculations.?

The other major one people use is Berger's Twist Rate Calculator, but as they don't make anything with a plastic tip it's probably in their best interests not to include it in their program. JBM's pages are a mine of information and my go to source for most calculations and bullet lengths.

 

[ndt man]

The other major one people use is Berger's Twist Rate Calculator, but as they don't make anything with a plastic tip it's probably in their best interests not to include it in their program. JBM's pages are a mine of information and my go to source for most calculations and bullet lengths.

Thanks for the information I had a feeling that was going to be the answer. I wonder how meny others have rejected tipped bullets as unstable using other twist rate calculators that do not have an option to add the tip length. ( I know I have)

 

[antsa]

The other major one people use is Berger's Twist Rate Calculator, but as they don't make anything with a plastic tip it's probably in their best interests not to include it in their program. JBM's pages are a mine of information and my go to source for most calculations and bullet lengths.

Yep, JBM's calculator IMO is the one to use. Specially if you use polymer tipped projectiles. There is a two-part technical paper on the rational behind the formula for those so inclined. Google will find it for you.

Cheers