Recommended twist rate / bullet weight

[mjes92]

I remember reading an article years ago recommending a given rifling twist rate for a specific range of bullets weights.

Does anyone have access to such a chart? (.223 Rem to be specific)

Or is my memory failing me?

Thanks

[Jimro]

With 223 you need to add barrel length to the equation.

A 1:9 twist 16" barrel will have a hard time stabilizing 75gr bullets, but make it a 26" barrel and you are doing fine. So the twist rate should be taken into consideration with barrel length.

From a 20" barrel (AR-15) this is a "general rule of thumb" for the common barrel twist rates.

1:12 = 55gr and lower
1:9 = 69 gr and lower
1:8 = 77gr and lower
1:7.7 = 80gr and lower
1:7 = 85gr and lower
1:6.5 = Specific for 90gr bullets

This is NOT gospel, I know shooters who shoot 80gr bullets from their 1:8 twist match barrels, what these are are guidelines about what you can expect in terms of stability. Also this is a list of weights, different bullet lengths for solid copper bullets do not apply, as they are longer than their cup and core counterparts. The military went to a 1:7 twist not because the SS109 bullet needed it, but because the tracer did.

For accuracy, choose the slowest twist that will stabilize your bullet of choice.

Jimro

[mehavey]

you need to add barrel length to the equation...

Good point, as rotational speed is the operating factor.

Lots of sites will give you the supposedly optimum "twist rate" for a nominal barrel, but is there
a Greenhill-type formula for required RPM? ...as a function of weight/specific gravity/length?

[Jimro]

Instead of using the Greenhill formula I recommend this calculator that uses the Miller Stability Formula: http://www.jbmballistics.com/cgi-bin/jbmstab-5.1.cgi

Jimro

[WWWJD]

Barrel length... is relevant because RPM is a function of twist rate AND velocity? Is that where this statement originates because RPM per bullet weight is what's really important?

I've not seen a chart that takes velocity into account either. If this is the case, then some of these bullet weight per twist rate charts are kind of debunked.. yes?

[Jimro]

WWWJD,

Twist rate charts are like burn rate charts, they tell a part of the story but not the whole story. If you compare different bullet lengths in the SAME cartridge and SAME barrel length, then twist rate charts make a lot of sense.

For different cartridges and different barrel lengths not so much. You can get a lot more velocity out of a 220 Swift or 22-250 than you can with a 223 Rem. This means that you can use a slower twist to achieve the same bullet rpm for stability. Play around with the JBM stability calculator and you can see how the variables interact.

Jimro

[BuckRub]

Use google and type in "Lilja twist rate"

[mjes92]

Great conversation,
Just what I was looking for.
Thanks Gentelmen