what about twist rates, use to your advantage

J

JRB

Guest
i was just pondering a new barrel in both my PPC BR rifle, and varmint rig, and wondered why some use a 13, 14 or even 15 in the PPC.
Is there an advantage in wind bucking with a tighter twist? more rpm's
what are the pros and cons?
i have heard varmint hunters say that a tighter twist will hit harder, or is this a myth?
Jim
 
As long as the bullet is properly stable it is my opinion that a looser twist will "buck wind better" but not enough to actually measure or quantify. It should show up as better aggs over time.

BTW, There is a long-standing myth that TIGHTER twists "buck wind better" which is just that, a myth.

Regarding the the varminter's belief that "tighter twists hit harder"........... this is most certainly true :)

Given the same velocity the tighter twist is carrying a bunch more energy AND will release it dramatically.

thinkabouddit.....

al
 
Does twist rate have anything to do with how fast a barrel wears, or in most cases does the powder born the barrel before the bullet wears it away?
say a PPC with a 8 twist vs 14
why do some shooter in BR choose a 13 or 14 when a 15 will work?
Jim
 
JRB said:
Does twist rate have anything to do with how fast a barrel wears,



..................... 13 or 14 when a 15 will work?
Jim
Click to expand...



IMO, NO

Scientifically, NO

According to Rinker ('Understanding Firearm Ballistics') NO

According to Harold Vaughn hissownself (I asked him) NO

I don't generally know why most people do things :)

Why I do things is generally because I've asked a specialist(s), then tested.
 
Faster twist is for longer bullets. Contray to the popular belief that twist rate is based on bullet weight, the actual twist is calculated on the bearing surface of the bullet (what is touching the lands.) Now on the other hand, bullet length IS directly related to weight, so you can guesstimate it that was as well. You really cant "over stabilize" a bullet by going with a faster twist. You can increase the Spin Drift at extended ranges, but i don't know if you'll be shooting to the ranges where you will notice that at all.

Heavier, longer bullet=Faster twist rate

~MMG
 
"Twist rate based on bearing surface"????

I've never heard of this.

Length-YES

Bearing surface??- nevah' heard of it....I have 68gr bullets with longer bearing surface than 105's. Ant the 105's definitely will keyhole most magickly you fire them from the barrel set up for the 68's!

Must be New Math

al
 
Berger 105 @ prox .365-.380

Quite a number of the older, blunter 68-70gr bullets have a bearing surface near on .400
 
MM,
I disagree with the part about bearing length being what twist is calculated from. I am pretty sure that it is the overall length of the bullet in calibers that is the determining factor, with some deference to shape if one is trying to work close to the line.
 
Boyd Allen said:
MM,
I am pretty sure that it is the overall length of the bullet in calibers that is the determining factor, with some deference to shape if one is trying to work close to the line.
Click to expand...

Why would the overall length matter at all with the twist rate? the only part effected by the twist is what is in contact with the twist. anything on the ogive that is smaller than the lands will have nothing to do with how the rifling engages.

I may be wrong, ya learn something new every day anyway.

MMG
 
MMGunsmithing said:
Why would the overall length matter at all with the twist rate? the only part effected by the twist is what is in contact with the twist. anything on the ogive that is smaller than the lands will have nothing to do with how the rifling engages.

I may be wrong, ya learn something new every day anyway.

MMG
Click to expand...

Let's see ya argue with THAT Boyd!!!

LOL

al
 
alinwa said:
"Twist rate based on bearing surface"????

I've never heard of this.

Length-YES

Bearing surface??- nevah' heard of it....I have 68gr bullets with longer bearing surface than 105's. Ant the 105's definitely will keyhole most magickly you fire them from the barrel set up for the 68's!

Must be New Math

al
Click to expand...
I figured you would be the one explaining this one Al.
 
I have seen- with my own eyes- a 22 cal bullet weighing 55 gr that is the same shape and length (essentially a carbon copy) of an 80gr VLD that didnt shoot from a 1:7,1:9, or a 1:12 so i dont know what kind of physics these bullets defy. Usually a vld in the 70+gr range needs a 1:9 where a 52 likes a 1:12. Btw dont ask about these bullets or what theyre constructed of i was just giving an example of what i see shooting lots of 22 cal bullets in lots of shapes and chamberings and hearing results from many people in what they see.
 
Dusty Stevens said:
I have seen- with my own eyes- a 22 cal bullet weighing 55 gr that is the same shape and length (essentially a carbon copy) of an 80gr VLD that didnt shoot from a 1:7,1:9, or a 1:12 so i dont know what kind of physics these bullets defy. Usually a vld in the 70+gr range needs a 1:9 where a 52 likes a 1:12. Btw dont ask about these bullets or what theyre constructed of i was just giving an example of what i see shooting lots of 22 cal bullets in lots of shapes and chamberings and hearing results from many people in what they see.
Click to expand...

Dusty

It's called overturning aerodynamic torque and is part of the definition/calculation of gyroscopic stability. Chapter 10 Bryan Litz's Applied Ballistics for Long Range Shooting
 
is Bryan Litz's Applied Ballistics for Long Range Shooting more or less the long range shooting and ballistics bible? I've heard several totally unconnected people on various forums give almost identical answers on twist calculation and mentioned this book.

MMG
 
MMGunsmithing said:
is Bryan Litz's Applied Ballistics for Long Range Shooting more or less the long range shooting and ballistics bible? I've heard several totally unconnected people on various forums give almost identical answers on twist calculation and mentioned this book.

MMG
Click to expand...

No,

it's just the newest one and Bryan has spent a lot of time on this forum. Been involved in some knock-down, drag-out brawls.....

Looooong before Bryan the definitive text was (still is) McCoy http://www.amazon.com/Modern-Exteri...F8&qid=1405731701&sr=8-11&keywords=ballistics

The funnest one is Vaughn http://www.amazon.com/Rifle-Accurac...4&sr=8-1&keywords=rifle+accuracy+facts+vaughn

The easiest one is Rinker http://www.amazon.com/Understanding...TF8&qid=1405731701&sr=8-5&keywords=ballistics



Boatright is confused, as are the Sierra Techs....


A topic search for ballistics may turn up some stuff altho The Mother Of All Ballistics Threads seems to have gone the way of the breaking wind.....
 
MMGunsmithing said:
is Bryan Litz's Applied Ballistics for Long Range Shooting more or less the long range shooting and ballistics bible? I've heard several totally unconnected people on various forums give almost identical answers on twist calculation and mentioned this book.

MMG
Click to expand...

The laws of physics and aerodynamics have never changed. The collection of data, organization and presentation varies with different authors. As Al said Bryan is just the latest and has done a very good job of presenting complex topics in layman's terms without getting bogged down in the mathematics. He puts to rest many old wives tails that just won't go away.
 
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