Bullet SG? Stability Analysis

[KCode]

So I was over on Berger's site because I came across a barrel that piqued my interest. I'm looking at getting a 300 blackout barrel and came across a 1:5 twist barrel which is the tightest twist I've personally seen for a 300 blackout barrel. Well this immediately triggered my remembrance of the 8.6 blackout and it's tight twist = its devastating characteristics.

Well I went to Berger's site to see if it would stabilize the 110gr Varmageddons I plan to run for defensive handloads in front of probably Lil Gun. This is what it came out to...I don't understand why the SG is so high and is that high of a number good?

 

[ma smith]

Alot of Bergers discussion on stability has to do with long range shooting and performance of the BC to predict trajectory. Obviously, very little of this applies to self-defense and QCB, since at these distances you don't really care about BC or bullet shape in terms of flight trajectory/accuracy in the same way.

IIRC this factor of stability reductively means your twist is 'enough' for the bullet to fly straight and not tumble or wobble, etc, So in this cas you are more than enough twist. Next step is to maybe calculate the RPM & double check your speed x twist isn't going to tear apart the bullet (or jacket) apart in mid flight.

 

[KCode]

Next step is to maybe calculate the RPM & double check your speed x twist isn't going to tear apart the bullet (or jacket) apart in mid flight.

I actually thought this is what this was calculating. How do I determine this then? Let's say I figure out the RPMs, how do you determine the bullets punching out point?

Edit: 316,800rpms

 

[ma smith]

I actually thought this is what this was calculating. How do I determine this then? Let's say I figure out the RPMs, how do you determine the bullets punching out point?

Edit: 316,800rpms

Roughly equivalent to firing same bullet ± 4,400 fps out of 1:10 twist

 

[KCode]

Roughly equivalent to firing same bullet ± 4,400 fps out of 1:10 twist

So how do you know what a bullet can withstand before it comes apart?

 

[Krob95]

Traditionally, 300,000 rpm is considered a "safe" max rpm with out bullets blowing up. But for reference I was running 95gr SMK's in a 6.5tw barrel at 362,000RPM and they all made it to target and it shot exceptionally well. Brought the speed down and my current load shows 320,000 rpm.


You will probably be ok with them.

 

[E. Bryant]

So how do you know what a bullet can withstand before it comes apart?

You test it and find out

It took me a while, but I've finally come around to the idea of having separate uppers for 300 BLK supers and subs. Go ahead and order that 1:5 barrel for subs, and then run an garden-variety barrel on the supersonic upper.

 

[spife7980]

I actually thought this is what this was calculating. How do I determine this then? Let's say I figure out the RPMs, how do you determine the bullets punching out point?

Edit: 316,800rpms

Nope, gyroscopic and dynamic stability does not measure anything to do with the bullets construction and ability to hold itself together.
Its how well the distributed mass in that spinning bullets wobble as it moves along its flight path keeps the bullet falling into its own path self correcting itself in flight and staying along a straight line. If the bullet doesnt have enough twist itll do poorly as the center of gravity overtakes the center of pressure and falls end over end as the bullet tumbles.

Bullet Stability

The details of gyroscopic and dynamic bullet stability

bisonballistics.com

Bullet Gyroscopic Stability Calculator

Calculate the Gyroscopic stability of a bullet with the Miller approximation.

bisonballistics.com