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Hank45
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rate of twist
Apr 28th, 2014 at 6:46am
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Is a 9.5 rate of twist to much for a paper patched bullet and black powder?  Thanks for your answer, Hank45 Smiley
  
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Schuetzendave
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Re: rate of twist
Reply #1 - Apr 28th, 2014 at 12:38pm
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No can answer your twist question unless they know what caliber you are shooting and the length of your bullet.
  
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Hank45
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Re: rate of twist
Reply #2 - Apr 29th, 2014 at 6:13am
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To Schuetzendave, the caliber is .28 and the length is 1.5 breech seated. Hank45 Smiley
  
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Schuetzendave
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Re: rate of twist
Reply #3 - Apr 29th, 2014 at 10:30am
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The Greenhill's formula indicates the maximum bullet length you can shoot in a 28 caliber is:

8.0:1 twist: max. 1.51" bullet
8.5:1 twist: max. 1.42" bullet
9.0:1 twist: max. 1.34" bullet
9.5:1 twist: max. 1.27" bullet
10.0:1 twist: max. 1.21" bullet
10.5:1 twist: max. 1.16" bullet
11.0:1 twist: max. 1.10" bullet

Therefore a 9.5 twist is not tight enough to properly spin a 1.50" bullet. Would have to go to a 8.0:1 twist.
If your barrel is a 9.5:1 twist then it would be better to select a bullet shorter than 1.27" long.
« Last Edit: Apr 29th, 2014 at 10:36am by Schuetzendave »  
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Chickenthief
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Re: rate of twist
Reply #4 - Apr 29th, 2014 at 6:52pm
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Greenhill is a bit "broad" regarding rifle bullets.

Use Don Millers excelent excel spread sheet:

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Schuetzendave
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Re: rate of twist
Reply #5 - Apr 29th, 2014 at 9:01pm
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Unable to use Miller spreadsheet calculation unless someone knows the weight of a 28 caliber bullet that is 1.5" long. However assuming about 350 grains:

Don Miller's Twist Rule                        
                       
                       
Caliber      0.284      Inches            
Bullet Weight      350      Grains      ?      
Bullet Length      1.5      Inches            
Barrel Twist      9.5      Inches/turn            
muzzle velocity      1500      fps            
Temperature      100      degrees Fahrenheit (59 is standard)            
Pressure      29.92      inches of mercury (29.92 is standard)            
                       
Sg =      2.35                  
                       
Sg shouldn't be less than 1.4.  If Sg is greater than about 2.0, you may                        
gain some accuracy by going to a slower twist barrel.                        
« Last Edit: May 1st, 2014 at 10:10am by Schuetzendave »  
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Dr Tom
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Re: rate of twist
Reply #6 - May 1st, 2014 at 12:27am
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Hmmm. Dusting off the slide rule. A 1.5 inch 28 cal. with a 2 caliber ogive, pure lead and 21 shallow grease grooves = about 240 grains. A twist of  8+ might work.
« Last Edit: May 1st, 2014 at 12:38am by »  
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Hank45
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Re: rate of twist
Reply #7 - May 1st, 2014 at 7:01am
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Dr.Dave, I plan on using a slick and paper patching it. thanks for your answer Hank45 Smiley
  
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Hank45
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Re: rate of twist
Reply #8 - May 1st, 2014 at 7:03am
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Dr. Tom, I am sorry the mistake with your name. Hank45
  
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Schuetzendave
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Re: rate of twist
Reply #9 - May 1st, 2014 at 10:21am
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Don Miller's Twist Rule                        
                       
                       
Caliber      0.284      Inches            
Bullet Weight      240      Grains            
Bullet Length      1.5      Inches            
Barrel Twist      9.5      Inches/turn            
muzzle velocity      1400      fps            
Temperature      80      degrees Fahrenheit (59 is standard)            
Pressure      29.92      inches of mercury (29.92 is standard)            
                       
Sg =      1.52      

Caliber      0.284      Inches            
Bullet Weight      240      Grains            
Bullet Length      1.5      Inches            
Barrel Twist      9.5      Inches/turn            
muzzle velocity      1650      fps            
Temperature      100      degrees Fahrenheit (59 is standard)            
Pressure      29.92      inches of mercury (29.92 is standard)            
                       
Sg =      1.67      

Caliber      0.284      Inches            
Bullet Weight      240      Grains            
Bullet Length      1.5      Inches            
Barrel Twist      9.5      Inches/turn            
muzzle velocity      1400      fps            
Temperature      32      degrees Fahrenheit (59 is standard)            
Pressure      29.92      inches of mercury (29.92 is standard)            
                       
Sg =      1.38                  
           
           
                       
Sg shouldn't be less than 1.4.  If Sg is greater than about 2.0, you may                        
gain some accuracy by going to a slower twist barrel.

                       
Weight of bullet has been estimated.
« Last Edit: May 6th, 2014 at 12:32pm by Schuetzendave »  
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MikeT
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Re: rate of twist
Reply #10 - May 1st, 2014 at 10:27am
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I think the Old Dead Guys were able to shoot PP bullets of considerable length out of slow twist barrels [45 caliber Long Range].
Try the 1.5" PP bullet and see how it goes.  At 200 yards, it may be just the ticket.

Keep on hav'n fun!
MikeT
  
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Dr Tom
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Re: rate of twist
Reply #11 - May 1st, 2014 at 11:05am
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With or without grease grooves, 1.5 inches is right on the edge of stability. If I owned your barrel, I'd certainly try it. 

Original Greenhill: 8.1
Bowman: 7.4
Miller: 9.1
Miller with corrections: 9.6

  
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Hank45
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Re: rate of twist
Reply #12 - May 4th, 2014 at 7:11am
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schuetezendave, what would the SD be if I dropped the weight of the bullet to 200 grains? Thanks for your answer Hank45 Smiley
  
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Schuetzendave
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Re: rate of twist
Reply #13 - May 5th, 2014 at 9:59am
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Don Miller's Twist Rule                        
                       
                       
Caliber      0.284      Inches            
Bullet Weight      206      Grains            
Bullet Length      1.245      Inches            
Barrel Twist      9.5      Inches/turn            
muzzle velocity      1400      fps            
Temperature      80      degrees Fahrenheit (59 is standard)            
Pressure      29.92      inches of mercury (29.92 is standard)            
                       
Sg =      2.25                  
     

Caliber      0.284      Inches            
Bullet Weight      206      Grains            
Bullet Length      1.245      Inches            
Barrel Twist      9.5      Inches/turn            
muzzle velocity      1650      fps            
Temperature      100      degrees Fahrenheit (59 is standard)            
Pressure      29.92      inches of mercury (29.92 is standard)            
                       
Sg =      2.46                  
     

Caliber      0.284      Inches            
Bullet Weight      206      Grains            
Bullet Length      1.245      Inches            
Barrel Twist      9.5      Inches/turn            
muzzle velocity      1400      fps            
Temperature      32      degrees Fahrenheit (59 is standard)            
Pressure      29.92      inches of mercury (29.92 is standard)            
                       
Sg =      2.05                  
     
                       
Sg shouldn't be less than 1.4.  If Sg is greater than about 2.0, you may                        
gain some accuracy by going to a slower twist barrel.                        

« Last Edit: May 6th, 2014 at 10:13am by Schuetzendave »  
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Hank45
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Re: rate of twist
Reply #14 - May 5th, 2014 at 3:02pm
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Schuetzendave, I have another bullet and the weight is 136 gn. can you give me the SD and Smiley Sorry for the bother and Thank for your answer Hank45
  
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