brainteaser aerodynamics

Silhouette · 11-01-2012, 11:20 PM

I know this is a pistol forum...but I've been teaching a young man who shows awesome potential, stemming from his natural ability. Before I start letting him sling lead downrange...I've been 'schooling' him on the basics of ballistics. Here is a question I threw together to test his reasoning...see how many of you can answer it (without Googling it)..LOL

Question Setup: For best accuracy at a given range, barrels should be matched to a particular bullet type and weight and fired at an optimum velocity.

Question: Each bullet has a specific ballistic coefficient based on sectional density and aerodynamic coefficient. As the ballistic coefficient designation increases, will the ideal twist rate increase or decrease?

It's actually not a difficult question to answer...but I've never seen this asked in almost 60 years of shooting and the study of ballistics. HAVE FUN!

retDAC · 11-02-2012, 03:06 AM

IIRC, increasing ballistic coefficient results in a longer bullet if all other factors are equal. And such longer bullet requires a faster twist.

If some of the 'other factors' are not the same or essentially so, then sometimes the same or even slower twist is mandated.

Silhouette · 01-19-2013, 09:06 PM

Sorry Dave...I can't do that... (had to borrow that line...LOL)
No...the longer bullet needs a faster twist rate...just read the history of the 5.56 NATO round and the M-16...

11-01-2012, 11:20 PM	#1
Silhouette Member Join Date: Oct 2011 Location: Florida Posts: 51	Brain Teaser (not) I know this is a pistol forum...but I've been teaching a young man who shows awesome potential, stemming from his natural ability. Before I start letting him sling lead downrange...I've been 'schooling' him on the basics of ballistics. Here is a question I threw together to test his reasoning...see how many of you can answer it (without Googling it)..LOL Question Setup: For best accuracy at a given range, barrels should be matched to a particular bullet type and weight and fired at an optimum velocity. Question: Each bullet has a specific ballistic coefficient based on sectional density and aerodynamic coefficient. As the ballistic coefficient designation increases, will the ideal twist rate increase or decrease? It's actually not a difficult question to answer...but I've never seen this asked in almost 60 years of shooting and the study of ballistics. HAVE FUN!

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11-02-2012, 03:06 AM	#2
retDAC Senior Member Join Date: May 2006 Location: near Huntsville, Ala. Posts: 707	IIRC, increasing ballistic coefficient results in a longer bullet if all other factors are equal. And such longer bullet requires a faster twist. If some of the 'other factors' are not the same or essentially so, then sometimes the same or even slower twist is mandated.

01-19-2013, 09:06 PM	#3
Silhouette Member Join Date: Oct 2011 Location: Florida Posts: 51	Sorry Dave...I can't do that... (had to borrow that line...LOL) No...the longer bullet needs a faster twist rate...just read the history of the 5.56 NATO round and the M-16...