TWIST VS VELOCITY?? TWIST AND VELOCITY?? WHAT SAY YOU?

[Edd]

Wow, reading comprehension still isn't your strong suit either I see....I agreed with you about the 1/10 not being sufficient. I said velocity/altitude make a difference to a certain point. Holy moly Edd it's not going to make up the difference between a 1/7 vs a 1/10 but it can and will make the difference between a 1/7 and 1/8.

Run that 115gr in the calculator with a 1/8 twist at 7,000' and 3250fps and see what it says.

Nope, it won't do that either. You would have to more than double the velocity to duplicate the SG increase of going from an 8" to a 7" twist.

I see you are trying to salvage some of your misinformation by sneaking altitude into the mix. Remember, the thread title was TWIST VS VELOCITY?? TWIST AND VELOCITY?? WHAT SAY YOU?

 

[Tiny Tim]

That 115 simply isn't going to stabilize in a 10 tw barrel. Not within the physics we have to accept. 16,000 fps may theoretically do it, but our powders won't get you there. Speed, temp, and altitude can give a little wiggle room if your close, but if you want to shoot heavies, you need a faster twist.

 

[adam32]

Nope, it won't do that either. You would have to more than double the velocity to duplicate the SG increase of going from an 8" to a 7" twist.

Then why does blackjack recommend a 1/7 for the 25 CM but a 1/7.5 or a 1/8 for the 257 Wby if velocity makes no difference?

No misinformation from me, but it's not my fault you're still an idiot that can't comprehend anything. It's no wonder pretty much every one has you blocked.

I said in my very first post that velocity AND altitude make a difference to a point, and that statement is still very true! Even if you can't understand it.

 

[Edd]

Then why does blackjack recommend a 1/7 for the 25 CM but a 1/7.5 or a 1/8 for the 257 Wby if velocity makes no difference?

No misinformation from me, but it's not my fault you're still an idiot that can't comprehend anything. It's no wonder pretty much every one has you blocked.

I said in my very first post that velocity AND altitude make a difference to a point, and that statement is still very true! Even if you can't understand it.

That is a question for Blackjack but sometimes bullets have a stress limit. Why don't you calculate the stability of those combinations and see what the stability really is instead of guessing or wanting an idiot to do it for you.

 

[rogerstep]

8x68s
tisk risk- a little friendly bantering is good for the grey matter.
Makes one get out the books for a bit instead of sitting watching the doom
and gloom screen. Also allows one to go dust off the math degree
hanging on the wall also.

 

[Len Backus]

Edd and Adam32

This will be your only warning.

No one comes to LRH to watch personal bickering.

 

[adam32]

That is a question for Blackjack but sometimes bullets have a stress limit. Why don't you calculate the stability of those combinations and see what the stability really is instead of guessing or wanting an idiot to do it for you.

I've done calcs on MANY bullets in many different twists and velocity and altitude combinations. That's how I know that velocity and altitude most certainly make a difference, TO A POINT! Like I've said multiple times now.

 

[Beluebow]

Twist rate trumps velocity when it comes to significant gains in stability.

Velocity and elevation play a role albeit a smaller one.

 

[Jeffrey Van Zandt]

I haven't seen this question asked around the website. I want to build a rifle that will shoot heavy for caliber bullets. All specifics aside, does driving a heavier, longer and better BC bullet faster thru a "standard" twist stabilize that bullet the same as driving that bullet more slowly thru a faster twist? Or, is the faster twist the only solution for stabilizing the heavier bullet regardless of velocity? I understand pressures will be proportionally greater the faster a bullet is driven no matter the twist.

In the specific, I can purchase a 10 twist, 6mm barrel but pertaining to my question, is that enough twist for a 115 grain bullet.

if I have a bullet I know I want to use I will get a barrel that is twisted for that bullet

 

[cohunt]

A lot of people are forgetting its not about projectile weight, its more about the overall length & bearing surface length in stabilization.

E.g I can shoot a 55gr nosler ballistic tip out of my .22-250 with 1:14 twist which most calculators will say is at the stabilization crest for the 1:14.

BUT I can successfully(and accurately) shoot a 70gr Speer spitzer out of the same 1:14 twist barrel.

WHY?

Both projectiles are nearly the same identical length, the Nosler is .810 long & the Speer is .808 long, so the heavier projectile is actually shorter by a whisker!
Not only that the bearing surface is almost the same.

So IF you could find a short 115gr projectile in .243 then it could theoretically be stabilised in a 1:10

It certainly will not work if the 115gr projectile is something like a VLD.

If you want to comfortably be able to shoot different/VLD projectiles in a .243 then I would be looking at a 1:8

Fully agree-- I had a "slow twist" 308w that I was playing with subsonic loads for--lots of guys running heavy 200gr + subs but with faster twist than I. So I started crunching numbers and found that I can run heavy round nose bullets very well in my slow twist barrel ....subsonic also brings in the velocity part of the equation, and I shoot at 8000+ which is brings in the altitude part of the equation too.

 

[Flatbow]

As stated the 115 will most. Likely not stabilize (depending on brand and bc) I am not too familiar with that caliber. However, you can make up some stability with velocity. I know as I have done it with my 7mm RUM using the burger ballistics calculator.
It is only possible if you are already very close

 

[Radman]

I haven't seen this question asked around the website. I want to build a rifle that will shoot heavy for caliber bullets. All specifics aside, does driving a heavier, longer and better BC bullet faster thru a "standard" twist stabilize that bullet the same as driving that bullet more slowly thru a faster twist? Or, is the faster twist the only solution for stabilizing the heavier bullet regardless of velocity? I understand pressures will be proportionally greater the faster a bullet is driven no matter the twist.

In the specific, I can purchase a 10 twist, 6mm barrel but pertaining to my question, is that enough twist for a 115 grain bullet.

It may not be what you want but here is what I use for minimum twist rate:

C over BL divided by BD, then all that times BD.
C = Constant
(150 for 1500-2800 fps
180 for over 2800 fps)
BL = Bullet Length
BD = Bullet Diameter

Hope this helps. I found this on the net a few years ago and have used it ever since. If anyone disagrees with it call 1-800-WHO-CARES
JMO, everyone has one.

 

[Ranger Rick]

for cripe sakes you guys!! does everything have to be an argument. state your opinion and back the EFF off!! sick of the argumentative hijacking from you !! you do nothing but lose the respect of those on this site who participate without being combative. I hope to see you get jacked off this site!

You have your answer, please close the post.

 

[adam32]

I just did a few calcs just for reference.

A Berger 115gr 6mm bullet at 2,850fps with a 1/7 twist at sea level has an SG of 1.65.

Same bullet, same everything but with a 1/8 it drops to a SG of 1.26. But then run it at 3,250fps and it goes up to 1.32. Not much of a difference but a gain.

Now, shoot that same bullet in a 1/8 at 3,250fps at 7,000' elevation and the SG bumps up to a 1.71...higher than the 1/7 can stabilize the bullet at sea level.

So in conclusion, velocity AND altitude can make a difference. Decide where you'll be hunting and how fast you'll be pushing the bullet then choose your barrel from there.