Twist Rate v Bullet Weight?

[Frenchieboy]

Now that I am getting into the more "technical" side of shooting and almost ready to start reloading my own ammunition maybe someone could help me understand the effects of different trist rates and how they tie in with different bullet weights. Is it normally the case (Purely as a generalisation) that a higher twist rate is needed for a heavier bullet head or that a lower twist rate is best for heavier bullet heads.

Then of course there is the question of is there any way of telling what twist rate your rifle barrel is please - I know my CZ527 in .222 is 1-12 but I am not sure what the twist rate is on my .243 - What markings (If any) should there be on the barrel to say what the twist rate is?

[mad1]

To check the twist on your barrel use a cleaning rod put the rod in then put a mark on the front near the handle towards you ...

When you push the rod in watch till the dot or mark goes 360* back facing towards you now measure how far the rod went down barrel ( if that makes sence )

So if it takes 12 inches to make a full revolution it's a 1:12 or 9 inches it's a 1:9 etc

M1

Edited June 27, 2013 by mad1

[Frenchieboy]

To check the twist on your barrel use a cleaning rod put the rod in then put a mark on the front near the handle towards you ...

When you push the rod in watch till the dot or mark goes 360* back facing towards you now measure how far the rod went down barrel ( if that makes sence )

So if it takes 12 inches to make a full revolution it's a 1:12 or 9 inches it's a 1:9 etc

M1

Thank you for that mad1. Something that I hadn't thought of!

[mad1]

Happy to help m8 ;-)

[Frenchieboy]

Just done that and found that my .243 has a 1-10 twist rate!

Isn't it strange how sometimes we overlook the simplest way to do things!

[mad1]

Double check your cz FB cos I have the same one in .223 I was told they are 1:9 but when I checked it it was 1:12 ? That explained why it didn't like 69+ grain !!!

[Frenchieboy]

My CZ527 has the original barrel and the spec says it is 1-12 twist. However to be on the safe side I will check it (When I have a spare minute) in the same way that you have suggested!

I should add that I have tried a few different weights of bullets from 50g upwards in my CZ 527 and it seems to prefer around the 53g Hornady weights but I haven't tried anything below 50g yet.

Edited June 27, 2013 by Frenchieboy

[casts_by_fly]

Now that I am getting into the more "technical" side of shooting and almost ready to start reloading my own ammunition maybe someone could help me understand the effects of different trist rates and how they tie in with different bullet weights. Is it normally the case (Purely as a generalisation) that a higher twist rate is needed for a heavier bullet head or that a lower twist rate is best for heavier bullet heads.

Then of course there is the question of is there any way of telling what twist rate your rifle barrel is please - I know my CZ527 in .222 is 1-12 but I am not sure what the twist rate is on my .243 - What markings (If any) should there be on the barrel to say what the twist rate is?

 

 

With twist rate, you need at least the minimum twist rate to stabilize the bullet you're shooting. Longer bullets need a faster twist. Longer bullets typically weigh more, but not in every bullet (compare a barnes all copper or a v-max to an equivalent weight round nose, or even worse a Berger VLD to a round nose). The length is what is important, but you can use weight as an approximate guide since most bullets are shaped similarly.

 

You can't overstabilize a bullet. Stabilization is simply spin. Consider a gyroscope. The faster you spin it, the more stable it is. The same goes for bullets. The problem with spinning them faster and faster is that imperfections in the weight distribution of the metals become more apparent and any weakness in the outer jacket can cause the jacket to rip apart at extremely high RPMs. That's why you don't see many 8 twist 22-250's designed for 40 gr bullets. Pushing a 40 gr at 3800 through an 8 twist is a recipe for vaporization. That said, plenty of guys in the US report very good results in a 223 with 40's and a 9 twist (that is Savage's standard twist rate in the 223). The 'normal' twist for a 223 is a 12, but there is a lot of sense in getting a 10 or 9 twist.

 

Twist and bullet length also explain why only some 243's will shoot some 100 gr bullets. A 100 gr 243 is long for caliber (at the higher end of the possible weights for that caliber) and most guns aren't designed to shoot long for caliber bullets. You then run into factory ammo that isn't pushing the bullet quite fast enough to generate enough RPM's to stabilize the bullet. In the end, you have iffy accuracy.

 

thanks

rick

[Frenchieboy]

An excellent explanation casts_by_fly, exactly what I was asking for.

Thank you!

[al4x]

just bear in mind with measuring it Frenchie that it does depend on a decent fit to get your rod to twist completely accurately

[Dekers]

just bear in mind with measuring it Frenchie that it does depend on a decent fit to get your rod to twist completely accurately

 

A New(ish) brush is usually pretty good!

 

...and you can use the whole barrel length as well and then do some maths, not simply 12" of it, possibly easier to do this a few times and check!

Edited June 27, 2013 by Dekers

[mad1]

My CZ527 has the original barrel and the spec says it is 1-12 twist. However to be on the safe side I will check it (When I have a spare minute) in the same way that you have suggested!

I should add that I have tried a few different weights of bullets from 50g upwards in my CZ 527 and it seems to prefer around the 53g Hornady weights but I haven't tried anything below 50g yet.

Yeah I though that but I was told cos mine is the varmint version it was a 1:9 but after doing a bit of research I found out they changed the twist one year ??

[rem708]

If you are using a thin jacket bullet then there is chance the jacket will come off if spinning too fast.

 

I regularly loaded Hornady 22 Cal .224 55gr SP SX™ in a pistol. I was working up the load and all of a sudden the point of impact disappeared. It took quite a few more shots before someone noticed a very distinctive cloud just beyond the end or the barrel. The bullet was living up to its name - super explosive and disintegrating with the velocity.

 

Unless you are pushing the bounds then I would not worry too much. Personally I like tighter twists as it give more options especially at long distance.

[PAULT]

I have shot every thing in mine from 55 gr nosler ballistic tips up to 100gr sp they were nearly all pretty accurate with a 1in 10 twist

[Underdog]

I use to use loads of Speer tnt in 22. They were limited to 3500fps. And 6mm had a speed limit.

Good bullet.

 

U.

[casts_by_fly]

The speer TNT was designed for varminting in the 222 and designed to be super explosive (thus the name). The standard twist for a 222 was a 12 twist, thus the limit was set for 3500 (a hot load in the 222 for 50 gr bullets). According to speer it was also a good bullet for the hornet, but often too long to feed reliably.

 

thanks

rick

[Underdog]

Yes used it in Hornet too.

Re shaped the cz plastic mag insert to alow a longer col and bobs yer unc :-).

 

U.

[Bewsher500]

- I know my CZ527 in .222 is 1-12 but I am not sure what the twist rate is on my .243

Are you sure?

I would be surprised if it wasn't 1:14

most factory .222 barrels are 1:14 (including my BRNO which is essentially the same as the CZ527)

most factory .243 barrels are 1:10

 

be that as it may don't overlook the fact that there are plenty of barrels which have no trouble at all spitting "heavy for calibre" bullets.

with marginal weights if often depends more on the bullet design and bearing surface (the part in contact with the lands) and the velocity they are pushed at than the barrel twist itself.

 

I have a factory .243 that will shoot 100gr loads all day long, slow loads, fast loads, flat base, boat tail, makes no odds

I also worked up a load for my .222 with a 1:14 twist.

"It will never stabilise 60gr bullets" they said

true, if you try to push them too fast

0.2gr increments above and below 20.6-20.8gr of N133 lead to 1-1.5" increases in group size going up to about 4-5" at around 21.4gr

messing with seating depth I could get anything between 2" to 1/2" groups with the same charge weight, deeper the better in this case

 

at 20.8gr and an OAL of 54.1 (tip not ogive) (which equates to around 2850-2900fps) it does this:

 

Edited June 27, 2013 by Bewsher500

[Underdog]

A quick check suggests 1-14" for the CZ 527 in 222, thats the same as my buddies years ago!

 

In saying that it would not be the first time an odd ball comes down the pipe!

 

U.

[Underdog]

I had a 1-16" Hornet once and that would not stablise 50grainers at all until I got a few round nose dumpy things (can't remember what they were) and then it would just about give a good field group.

 

Every 1-14" Hornet I had there was never an issue with modern long 50grainers. Even 55grainers.

55 Btips were never an issue in my 222's.

 

Never tried a 60 but heard of some that did!

 

I have heard of issues with too light a bullet and fast twists, I called it over stabilisation! One guy said he could not get a particular 50grain factory load to shoot well at all in his rifle (223, thats all I remember) so I asked him what the twist was, 1-9"! I suggested to try some 60grain. Next I heard it was fine! May not of been the twist but I have heard of light pills in fast twists causes the bullet to yaw!

 

U.

[Frenchieboy]

I stand corrected . After double checking on the CZ web site it seems that the 527 in .222 does in fact have a 1 in 14 twist rate. I haven't checked the barrel but there is no reason to disbelieve this as it is the standard factory barrel.

[1066]

The Greenhill formula was designed for just this problem, it's not exact, more of a rule of thumb but it has served it's purpose for well over a hundred years and still used today - There are several online calculators that are easy to use:-

 

http://kwk.us/twist.html

 

http://www.montanabulletworks.com/page11.html

[fieldwanderer]

There's a half decent calculator on the Berger (iirc) site, trouble being, I've found very few figures for bullet lengths

[JonathanL]

 

 

With twist rate, you need at least the minimum twist rate to stabilize the bullet you're shooting. Longer bullets need a faster twist. Longer bullets typically weigh more, but not in every bullet (compare a barnes all copper or a v-max to an equivalent weight round nose, or even worse a Berger VLD to a round nose). The length is what is important, but you can use weight as an approximate guide since most bullets are shaped similarly.

 

You can't overstabilize a bullet. Stabilization is simply spin. Consider a gyroscope. The faster you spin it, the more stable it is. The same goes for bullets. The problem with spinning them faster and faster is that imperfections in the weight distribution of the metals become more apparent and any weakness in the outer jacket can cause the jacket to rip apart at extremely high RPMs. That's why you don't see many 8 twist 22-250's designed for 40 gr bullets. Pushing a 40 gr at 3800 through an 8 twist is a recipe for vaporization. That said, plenty of guys in the US report very good results in a 223 with 40's and a 9 twist (that is Savage's standard twist rate in the 223). The 'normal' twist for a 223 is a 12, but there is a lot of sense in getting a 10 or 9 twist.

 

Twist and bullet length also explain why only some 243's will shoot some 100 gr bullets. A 100 gr 243 is long for caliber (at the higher end of the possible weights for that caliber) and most guns aren't designed to shoot long for caliber bullets. You then run into factory ammo that isn't pushing the bullet quite fast enough to generate enough RPM's to stabilize the bullet. In the end, you have iffy accuracy.

 

thanks

rick

 

You can, apparently. The nose of the bullet is supposed to follow it's trajectory so that the projectile is presenting it's minimum amount of surface area to the direction in which it is travelling so that the air moves over it efficiently.

 

If you stabilise it too much it travels in a sort of nose-up attitude so that its bearing surface is causing more drag.

 

The picture on post 44 of this link illustrates what I mean;

 

http://www.shootersforum.com/ballistics-internal-external/61476-ballistics-question-engineering-course-3.html

[wymberley]

trouble being, I've found very few figures for bullet lengths

Google, 'JBM bullet length list'.