Saubier.com  



Go Back   Saubier.com > Saubier.com Forums > Small Caliber Discussion Board

Reply
 
Thread Tools Display Modes
  #11  
Old 10-03-2021, 02:52 PM
moorepower moorepower is offline
Senior Member
 
Join Date: Mar 2011
Posts: 1,549
Default

I am pretty sure his goal is spinning the bullet faster for a more violent impact. When loaded with CFEBLK or A2200 you can get to 3600 fps, and that combined with a 1/7 would really perform well. I think you might loose a little velocity, but it sounds like a good plan to me!
Reply With Quote
  #12  
Old 10-03-2021, 04:44 PM
Bill K Bill K is offline
Senior Member
 
Join Date: Aug 2012
Location: N.E. Kommie Kalifornia
Posts: 6,304
Default

I believe the more violent damage it caused by a more fragile bullet and it's construction, rather than the speed it is turning. Could be wrong on that, but I believe the bullets make up has more too do with the damage done to what it hits.
Reply With Quote
  #13  
Old 10-03-2021, 05:44 PM
Dean2 Dean2 is offline
Supporting Member
 
Join Date: Jan 2010
Location: Alberta
Posts: 2,497
Default

Bullet construction is a facet for sure, however, the same thin skinned bullet spun faster definitely expands more violently. Thus my example of the Hornady 50 grain SPSX disintegrating in flight out of a 1:7 but not out of a 1:12 at 3500 fps. It is also why Hornady limits their velocity recommendation to 3600 fps and recommends the slightly thicker skinned 55 grain SPSX for the higher speeds of the 22-240 and 220 Swift due to their higher muzzle velocities. If RPM didn't affect expansion no bullet would blow up in flight, only after it hit something. If you calculate the difference in the rpm of the bullet imparted by two twists you will easily see why it happens. The faster twist creates a very significant increase in RPM.

Here is a simple formula for calculating bullet RPM:

MV x (12/twist rate in inches) x 60 = Bullet RPM

Quick Version: MV X 720/Twist Rate = RPM

Example One: In a 1:12″ twist barrel the bullet will make one complete revolution for every 12″ (or 1 foot) it travels through the bore. This makes the RPM calculation very easy. With a velocity of 3000 feet per second (FPS), in a 1:12″ twist barrel, the bullet will spin 3000 revolutions per SECOND (because it is traveling exactly one foot, and thereby making one complete revolution, in 1/3000 of a second). To convert to RPM, simply multiply by 60 since there are 60 seconds in a minute. Thus, at 3000 FPS, a bullet will be spinning at 3000 x 60, or 180,000 RPM, when it leaves the barrel.

Example Two: What about a faster twist rate, say a 1:8″ twist? We know the bullet will be spinning faster than in Example One, but how much faster? Using the formula, this is simple to calculate. Assuming the same MV of 3000 FPS, the bullet makes 12/8 or 1.5 revolutions for each 12″ or one foot it travels in the bore. Accordingly, the RPM is 3000 x (12/8) x 60, or 270,000 RPM.
Reply With Quote
  #14  
Old 10-03-2021, 07:07 PM
Gale Johnson Gale Johnson is offline
Senior Member
 
Join Date: Oct 2013
Location: Imperial, NE
Posts: 320
Default 221 fb

I am leaning towards a 1-7, I have used AA2200 achieving 3500 with the 40 gr VMax easily, very good varmint round, fairly explosive already

thank you all for the great conversation
Reply With Quote
  #15  
Old 10-03-2021, 10:23 PM
NeilA. NeilA. is offline
Senior Member
 
Join Date: Dec 2012
Location: Western Washington
Posts: 302
Default

Yes, my .221FB fast twist (1;7) is still doing well! 18.8 gr 1680 and a 40 gr vmax is my standard load. I’ll go 200-250 rds. Between cleanings out on the prairie, which I prefer.

Because so much of the energy is spent rotating the bullet, it does poop out beyond 200-220 yds or so. I can watch the squirrels spin when hit- it does splat them. Accuracy was 3/8ths inch at 100 last time I checked. I avoid shooting any critters closer than 30yds, because of flying splat.
Reply With Quote
  #16  
Old 10-04-2021, 01:09 AM
Bayou City Boy Bayou City Boy is offline
Supporting Member
 
Join Date: Sep 2006
Location: Tomball/Klein, Texas
Posts: 3,989
Default

Quote:
Originally Posted by neila. View Post
yes, my .221fb fast twist (1;7) is still doing well! 18.8 gr 1680 and a 40 gr vmax is my standard load. I’ll go 200-250 rds. Between cleanings out on the prairie, which i prefer.

Because so much of the energy is spent rotating the bullet, it does poop out beyond 200-220 yds or so. I can watch the squirrels spin when hit- it does splat them. Accuracy was 3/8ths inch at 100 last time i checked. I avoid shooting any critters closer than 30yds, because of flying splat.

Lol..........


-BCB
__________________


I miss mean Tweets, competence, and $1.79 per gallon gasoline.

Yo no creo en santos que orinan.

Women and cats will do as they please. Men and dogs should relax and just get used to the idea.

Going keyboard postal over something that you read on the internet is like seeing a pile of dog crap on the sidewalk and choosing to step in it rather than stepping around it.

If You're Afraid To Offend, You Can't Be Honest - Thomas Paine

Last edited by Bayou City Boy; 10-04-2021 at 01:12 AM.
Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT. The time now is 09:52 PM.


Powered by vBulletin® Version 3.8.1
Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.