Saubier.com  



Go Back   Saubier.com > Saubier.com Forums > Small Caliber Discussion Board

Reply
 
Thread Tools Display Modes
  #21  
Old 04-26-2017, 12:05 PM
GrocMax GrocMax is offline
Senior Member
 
Join Date: Oct 2012
Location: McKinney TX
Posts: 488
Default

Stability
Input Data
Caliber: 0.204 in Bullet Weight: 40.0 gr
Bullet Length: 0.749 in Plastic Tip Length: 0.110 in
Muzzle Velocity: 3750.0 ft/s Barrel Twist: 12.0 in
Temperature: 40.0 °F Pressure: 29.92 in Hg
Output Data
Stability: 1.093
26-Apr-17 05:57, JBM/jbmstab-5.1.cgi

Stability
Input Data
Caliber: 0.204 in Bullet Weight: 40.0 gr
Bullet Length: 0.749 in Plastic Tip Length: 0.110 in
Muzzle Velocity: 3750.0 ft/s Barrel Twist: 12.0 in
Temperature: 90.0 °F Pressure: 26.92 in Hg
Output Data
Stability: 1.336
26-Apr-17 05:59, JBM/jbmstab-5.1.cgi

A baro of 26.92 is like 3000 ft elevation.
Reply With Quote
  #22  
Old 04-27-2017, 06:02 PM
Ratbuster Ratbuster is offline
Senior Member
 
Join Date: Aug 2015
Location: Near Sacramento
Posts: 177
Default

Quote:
Originally Posted by chuckshooter View Post
check your numbers, that's not what I get
You are correct. I went back on the calculator and it had retained the numbers from yesterday. The tip length somehow changed from my original entry of
.130 to .350. That accounts for the discrepancy. Thanks!
Reply With Quote
  #23  
Old 04-27-2017, 07:19 PM
Ratbuster Ratbuster is offline
Senior Member
 
Join Date: Aug 2015
Location: Near Sacramento
Posts: 177
Default JBM Calculator

I am just beginning a new 17 Hornet build. I believe the vast majority of 17 cal barrels employ a 9 twist. Using the following parameters the JBM says a 9 twist substantially overstabilizes a 20 grain Vmax:

Twist: 9
Bullet Length: .538
25.5 mm Hg (about 4000' altitude)
Tip length: .130
Temp : 59 F

SG: 2.663

The bullet is even overstabilized with a 10 twist according to the JBM calculator

OTOH the Berger calculator says a 9 twist has a SG of 1.6, much better
Reply With Quote
  #24  
Old 04-27-2017, 07:33 PM
Ratbuster Ratbuster is offline
Senior Member
 
Join Date: Aug 2015
Location: Near Sacramento
Posts: 177
Default Twist rate

I called Berger tech about factoring the plastic tip length into the equation. The person I spoke to was familiar with this topic who said because they do not offer bullets with plastic tips they have not done any testing to determine how a tip might affect the calculations. In general they feel the plastic tip should not be treated any differently because it has no effect on the bearing surface of the bullet. That makes sense to me.
Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT. The time now is 10:14 AM.


Powered by vBulletin® Version 3.8.1
Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.