Cast bullet profile.

[300blk]

Let describes a profile (radius ?) as 5r or2r etc. can someone please explain how this is measured? And how to duplicate this on a lathe?
Thanks
300blk

[Iron Mike Golf]

The "R" stands for radius and means the radius of the projectile (half the projectile's diameter). The number is a multiplier of that radius.

Ogives are circular arcs. The amount of curvature is expressed by the radius of that circular arc. The bigger the number, the gentler the curve. Also, the bigger the number, the lower the drag.

Here's a good article: http://www.accurateshooter.com/ballistics/tangent-vs-secant-vs-hybrid-ogive-bullets/

Can't help you on lathe setup.

[300blk]

So 5r .312 boolit: .156 x 5= .78 inches from Beginning to end of ogive? A constant gradual curve?
Secant seems like it might not hold up as well with a extreme radius like 5r with cast lead. I need a way to draw this up. Any help would be appreciated. And any corrections to my understanding of this concept are as well.
Thanks again.

[300blk]

I guess what I'm missing is how to determine the radius of that circular arc. How is that done?

[robroy]

You calculated right but applied the number wrong. .78 is the radius of the ogive. To draw the radius start at the tangent point of the boolit's side to the ogive and measure .78 along a line that is perpendicular to the boolit's centerline. That point is the center of the .78 (5r) ogive. scribe that arc to the center line of the boolit and you will see half of the profile. Then just mirror that for the other side. I hope that is some what clearer than mud.

[Tom Myers]

I guess what I'm missing is how to determine the radius of that circular arc. How is that done?

All you ever want to know about a tangent ogive radiused nose.

Precision Ballistics Tangent Ogive (http://www.tmtpages.com/tech/tangent_ogive.htm)

More about ogives (http://www.tmtpages.com/draw/Helpfiles/Bullet_Design_Help.html)

scroll down and click on "nose detail"

[kevmc]

And how to duplicate this on a lathe?

300blk

Is this to make a top punch for sizing/seating or ???:?:

[300blk]

This is to make a cherry for a brass mold. I work as a manual machinist at a large, well outfitted machine shop here in Arkansas. I may just program this for CNC, but it would be more fun if I can accomplish it on a manual lathe.
It may be a bit yet, but when I have a design finalized (and drawn in SW) I will post it here for peer review, and if received well at all release it for anyone to take to the mold maker of their choice. Mostly I am doing this for fun and allow me to do some cheap r&d for a good heavy blackout hollow point, and a dedicated long range high BC boolit for the Garand.

[kevmc]

This is to make a cherry for a brass mold. I work as a manual machinist at a large, well outfitted machine shop here in Arkansas. I may just program this for CNC, but it would be more fun if I can accomplish it on a manual lathe.
It may be a bit yet, but when I have a design finalized (and drawn in SW) I will post it here for peer review, and if received well at all release it for anyone to take to the mold maker of their choice. Mostly I am doing this for fun and allow me to do some cheap r&d for a good heavy blackout hollow point, and a dedicated long range high BC boolit for the Garand.

Very cool!!!
I can appreciate the pride of doing it manually!!!

[williamwaco]

You Go MAN !

I wish I had the opportunity and the skills to try something like that.

[300blk]

Very cool!!!
I can appreciate the pride of doing it manually!!!

:) for sure, The more I look at this the more its looking like some time on the mazak inegrex is in my future. if it were a truncated cone or spire point or even a round nose I know how to do it manually, the old engine lathe I had been using primarily bit the dust, so the shop president came and asked me if I wanted a new one. It was like christmas. its a new (non US) south bend tool room lathe. and if i foo my part seems to hold .0002 or so tolerance. if i can figure it out, this machine will do it.

[300blk]

You Go MAN !

I wish I had the opportunity and the skills to try something like that.

Thanks!

I always wanted it also. the downside to working in a machine shop is the note book I have that has personal projects 3-4 months ahead at all times. unlike many labors of love, your time must be considered as a cost. if i can get a blank 2 cavity mold from lee for 20$ is it worth spending 2-3 hours designing and cutting my own?

I have a few neat ones ahead though, now that we have a wire EDM I am going to make a r700 (closer to surgeon design) action and build my own bolt action from the ground up. that's exciting.