Does a plastic tip , mean I can get away with a slower twist ?

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bruce moulds
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Joined: Sun Jun 19, 2005 4:07 pm

Re: Does a plastic tip , mean I can get away with a slower twist ?

#16 Postby bruce moulds » Mon Sep 03, 2018 7:37 am

further to the above, experience has shown that you need to shoot the bullet in 100 yd/mt increments out to the full range.
sometimes bullets will have a little wobble, and then straighten up again.
this can be a problem, as when wobbling, b.c. goes down temporarily.
not so bad if they all do it the same!
suspicion is that this will manifest itself most going into and out of the transonic zone, mach 1.2 to mach 0.8, but also in that zone.
only holes in the target will show this.
shortenig the bullet seems to help with the issue.
shooting at longer ranges, an sg higher than 1.4 seems to help.
it is said in urban myth that spin decay is not an issue, but it exists more than commonly believed.
remember the 30 cal 168 sierra shot from 11 and 10 twist barrels.
keep safe,
bruce.
"SUCH IS LIFE" Edward Kelly 11 nov 1880
http://youtu.be/YRaRCCZjdTM

GSells
Posts: 339
Joined: Sun Aug 13, 2017 11:04 pm

Re: Does a plastic tip , mean I can get away with a slower twist ?

#17 Postby GSells » Mon Sep 03, 2018 5:10 pm

Hi Bruce , totally agree with the above ! It’s funny how U mention about 168 smk’s . As Litz said that they shouldn’t be shot beyond 600 m and the dynamic stability goes south because of the sharp boat tail angle . Hence a faster twist than what miller formula predicts . This is just me saying this as others have different experiences . But a Berger 180 in a 9 twist the accuracy goes off a little at 1000 yds shooting below 2800 FPS and the JBM show stability going into the yellow at those speeds , even though it’s well above speed of sound. Every barrel is different and maybe that would explain the different accounts . The Bergeras may work fine in light conditions but for me , they seem to struggle in my barrels in a 9 twist below 2800 FPS at a 1000 yds . Mind u I’ve only ever done with my 7-08 ai and no major formal testing has been done. But once bitten , twice shy . I won’t be sending Bergers down range at 1000 yds under 2800 FPS . The ELD’s , well I can’t wait to !! Be very interesting!!

!Peter!
Posts: 99
Joined: Sun Oct 30, 2016 6:35 am

Re: Does a plastic tip , mean I can get away with a slower twist ?

#18 Postby !Peter! » Tue Sep 04, 2018 11:38 am

Graham,
The JBM screen shot you posted jogged my memory about a third paper from Courtney on twist, so I did some digging found it and a spreadsheet to calculate it. I haven't verified the spreadsheet.

Enjoy!
!Peter!
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