twist rate vs velocity

declan1980

does the twist rate of a rifle have an affect on the muzzle velocity?

Cass

Yes.

Not only does it effect MV, but also accuracy. The faster the twist rate the more friction the bullet has and the slower it exits the muzzle. It may be only a matter of 50 or so fps, but there is a difference hence the reason for different twist rates for different weighted bullets.

With regards to accuracy, if the bullet is spinning too fast and cannot stabilise obviously you will loose accuracy, and there is the rare event when the bullet can "destroy" itself from excessive RPM after leaving the barrel. This is also down to a hot load, in a fast twist rate barrel.

declan1980

thanks, i was wondering about that for a while. thats probably why my mv appears to be about 70 fps slower than the stated velocity of the rounds i'm using.

Jonty

declan1980 wrote: »

thanks, i was wondering about that for a while. thats probably why my mv appears to be about 70 fps slower than the stated velocity of the rounds i'm using.

the stated velocity on the box might be with a 26 inch barrel. I reckon you're doing well to get within 70fps.

tomcat220t

declan1980 wrote: »

does the twist rate of a rifle have an affect on the muzzle velocity?

What lenght and twist rate is your barrel ?

Tackleberrywho

I have often wondered is there a magic twist/barrel length rate.

For example will a faster twist work better on a shorter barrel if the calibre is the same.

eg 26" .223 Vs 20" 1/12 Vs 1/9 etc

the reason being making as short a barrel as possible; yet retaining Muzzle velocity

Case in point Remington VSSF II Vs VTR

declan1980

Jonty wrote: »

the stated velocity on the box might be with a 26 inch barrel. I reckon you're doing well to get within 70fps.

the stated velocity is with a 1:12 twist 24" lilja barrel

tomcat220t wrote: »

What lenght and twist rate is your barrel ?

my barrel is a 1:8 twist 24" tikka

tomcat220t

declan1980 wrote: »

the stated velocity is with a 1:12 twist 24" lilja barrel

my barrel is a 1:8 twist 24" tikka

I had a sako 75 with a 1-8 twist 24" barrel aswell and with 75gr hornady, it was 170fps off factory stated velocity .So id say your doing quite well to be getting the speed your getting .I also know that the C/Z varmint with a 1-9twist will shoot the 75 gr hornady with a 24" barrel well .

tomcat220t

Tackleberrywho wrote: »

I have often wondered is there a magic twist/barrel length rate.

For example will a faster twist work better on a shorter barrel if the calibre is the same.

eg 26" .223 Vs 20" 1/12 Vs 1/9 etc

the reason being making as short a barrel as possible; yet retaining Muzzle velocity

Case in point Remington VSSF II Vs VTR

If it was a .223 just for foxing i would build it around the new 53gr hornady round .

Hondata92

declan1980 wrote: »

the stated velocity is with a 1:12 twist 24" lilja barrel

my barrel is a 1:8 twist 24" tikka

Was wondering what make of barrel hornady used to test velocity

Where did you see that it was lilja though as i havent seen it mentioned on the hornady or lilja websites

stick shooter

Im not sure where but i saw LILJA being mentioned with hornady before on the net I do believe they work very well together

declan1980

tomcat220t wrote: »

If it was a .223 just for foxing i would build it around the new 53gr hornady round .

i'd really love to get my hands on some of that stuff, the figures look really impressive

FISMA

Good Question - short answer - not sure. Best guess - not really.

Quick history lesson - in the old days there were smooth bore ball muskets that clogged easily. Someone got the idea to put a groove down the bore, to allow fouling a channel in which to go in order to continue firing. This groove was called rifling.

After the rifling was completed, the musket that could barely hit a door at 100ya was dropping targets at 300ya and beyond.

Someone stumbled onto spin stability. Ever see the lads playing rugby shoot the ball in a nice spiral? Again, spin stability.

Twist rates cause spin stability. Too little spin and the round does not have enough rotational motion to be stable. Too much and the round may not be strong enough to hold itself together and could spin apart.

As the round goes down the barrel we have rotational motion and translational motion.

For a 24" barrel in 1:8 the round will rotate 3 times, for 1:12 only twice. That's only one rotation difference. Even in the bigger rounds, that's what - one inch more distance for the tighter spin? Given that barrels easily exceed that in variance doesn't seem that detrimental.

It does make sense that rotating more means more friction, thus, lower muzzle velocity.

But I could also be convinced that the rotational motion makes the translation motion easier - like screwing a screw rather than forcing it through.

Also, a tighter twist will mean more of the barrel has been cut out (for the groove) and not available for contact.

It wouldn't surprise me if there was actually less friction on the tighter twist.

Have to ask the experts on this one. For example, the translational motion could be a linear relationship whereas the rotational quadratic - like x^2, or x^3.

I'll have to think some more. It would be interesting to calculate the total contact area of a bullet through a barrel - only factors changing being grooves: 1:8 and 1:12.

Shouldn't be that difficult.

Famous last words!

Also, remember that barrel length is key. When the powder ignites gasses push on the bullet and accelerate it down the barrel. The longer the time the Forces by the gasses act on the bullet, the greater muzzle velocity. It's Impulse. Impulse = Force * time.

So again, even though the round may have to contact more surface area, there's still a Force acting on it, trying to accelerate it.

declan1980

Hondata92 wrote: »

Was wondering what make of barrel hornady used to test velocity

Where did you see that it was lilja though as i havent seen it mentioned on the hornady or lilja websites

i'm sorry i made a mistake with that comment, it was nosler that use lilja barrels to test their loads, but it was still a 1:12 twist they used.
so i guess we still dont know what type of barrel or twist rate hornady use, but they do say they use a 24" barrel

stick shooter

Hondata92 wrote: »

Was wondering what make of barrel hornady used to test velocity

Where did you see that it was lilja though as i havent seen it mentioned on the hornady or lilja websites

There was an article done by professional writer john haviland and published by varmint hunter magazine, In which he clearly states lilja have supplied barrels to all major bullet manufactures including hornady ,For the purpose of accuracy and also chamber pressure testing .