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  #1  
Old 05-10-2015, 09:22 AM
NZVarminter NZVarminter is offline
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Default 20 Br with 55g Berger, what twist

I've got a 20Br which has a 1:10 twist PacNor barrel. Initially I was shooting the 39 Sierra's, but I've now gone to the 55 berger and they seem to shoot ok at around 360-3700fps.

I've put about 1200 rounds down this barrel now, so am planning for another barrel to replace once its shot out that will be dedicated for the 55g bergers.

I see that the Berger site says the 55's need a 1:8 twist, and have read a few guys are happy with 1:9, but not many shooting them with a 1:10 twist.

What twist is best for the 55's?
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  #2  
Old 05-10-2015, 11:47 AM
rich44 rich44 is offline
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Default 9 twist

I have a 20br and 20-250 both 9 twist Pacnor barrels and both will shoot the 55 Bergers very well with the BR sometimes shooting in the .2's with RL15.
I know that Berger recommends a 8 twist but I don't think that is necessary in my experience shooting these two rifles.
You said your 10 twist was shooting them OK what is your definition of OK , I was thinking of trying a 10 twist on my next barrel, I have a 10 twist 204 that shoots the 50gr Bergers very well I haven't tried the 55's in it but maybe I should.
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Old 05-10-2015, 12:42 PM
Chickenthief Chickenthief is offline
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Using Don Millers formula:

http://www.google.dk/url?sa=t&rct=j&...92885102,d.bGg

V0=3700fps

1:10" gives Sg=0.97
1:9"" gives Sg=1.20
1:8" gives Sg=1.52
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Old 05-10-2015, 01:52 PM
andy221 andy221 is offline
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Quote:
Originally Posted by Chickenthief View Post
Using Don Millers formula:

http://www.google.dk/url?sa=t&rct=j&...92885102,d.bGg

V0=3700fps

1:10" gives Sg=0.97
1:9"" gives Sg=1.20
1:8" gives Sg=1.52
In addition to what chickenthief has posted. Berger has stability calculator on their web site. I don't know if their program calculates the SG the same as miller but, berger say that an SG of 1.1-1.5 is marginally stable. Bryan litz has explained that a bullet in their marginally stable window loses b.c. not accuracy and is not unstable.

He has also said that bullets do not become over stable in a fast for bullet weight twist barrel, once they become stable they are stable. The ill effects you may see are from the bullet being unbalanced. And with today's high quality bullets you will most likely not have issues and not be able to see a difference on paper. If your rifle will not shoot a light bullet in your fast twist it is not from the quality of the bullet or the fast twist but, is most likely that you barrel does not like the powder,bullet, or primer.

Bryan litz has section on accurate shooter now where people can start threads and ask questions. He has explained things in his book and has answered some good questions. Anyways there's some good info overv there if you want to check it out.
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  #5  
Old 05-10-2015, 02:09 PM
17VLD 17VLD is offline
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Default I would pick...

A Pac-Nor 8.5 because my 9 twist shoots 55's ok but did much better with the 50's.I also have a 12 twist that shoots the 50's and 40's very well.
Curious about your altitude also,I'm at 6202' and I know that helps in the 12 20BR.The 9 is a 20Dasher and pushes the 55's at 3750.i just think a little more twist would be beneficial.I don't think a guy has to go all way to an 8.just my .02 I checked Bergers stability site and they show a 9 twist 55 at 3600 fps having a sg of 1.49 which is right at the edge of stable and comfortable stable.I just think I would try the 8.5 to wring out some more accuracy.
Matt
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Last edited by 17VLD; 05-10-2015 at 02:21 PM.
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  #6  
Old 05-10-2015, 02:57 PM
Tim Anderson Tim Anderson is offline
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Some BR. shooters use the slowest twist possible for a given weight and to also match the size of case they are using.. Too much twist with a bullet moving at a hi vel. can cause the bullets to go poof.. I found this out with my 20x47 Lapua using a 1-9" twist. Have not got around to it to try but believe a 1-10" twist would be a better choice with a 55 gr. bullet used in one of the larger cases like the 20x250 or 20x47 lapua and a 1-9 or 1-8.5 would be better suited for the smaller cases like the 204. good luck.
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Old 05-10-2015, 03:22 PM
trotterlg trotterlg is offline
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I think the biggest drawback with an over stable bullet is that it ends up flying nose high at long ranges, so as the range increases the bullets BC decreases. The calculators also assume the spin rate decreases at the same rate as the velocity decreases which is not true, the spin rate decreases much slower than the bullet velocity, so the point that the bullet goes unstable according to the calculator will be far shorter than where the bullet really goes unstable, likely at the point where it goes subsonic. Learned about this a very long time ago when I had a very slow twist 22-250, believe it was a 1 in 17, but it would shoot 55gr bullets stable to at least 100 yards. Larry
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Old 05-10-2015, 03:51 PM
410gauge 410gauge is offline
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trotterlg and Tim Anderson, I have been shooting the 20 Br for quite some time with a 1:9 twist Barlein 26" barrel using the Berger and Blackhole 55 gr bullets. Almost 700 rds through this barrel now and still shooting very well (.3-.4" MOA to 500 yards). I have not had any "poofs". Velocity 3650 fps average. I am just fixing to chamber a larger capacity 20 caliber case strictly set-up for the Berger 55's. Capacity will be a little more than the .20-250. I have both 1:9 and 1:11 Kreiger barrel blanks available for the project. I would like your opinions on which twist? I'm looking for about 3800-3900 fps MV with this bullet, and I'm only interested in shooting this round beyond 500 yards. It should be able to stay above subsonic well past a 1000 Yards. Any comments would be appreciated. 410gauge
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Old 05-10-2015, 04:55 PM
trotterlg trotterlg is offline
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That is well out of my comfort zone of knowledge, I would try your bullets out of a 1 in 12 twist and see if they are stable at 100 yards using a 20BR, if that would work for you then I would say to go with the 11 twist, my 20BR is a 1 in 12 but I only use it for light bullets and it works out fine, if I had any heavy 20's I would put a few down range and let you know what they did. Larry
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  #10  
Old 05-10-2015, 05:10 PM
Tim Anderson Tim Anderson is offline
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I was trying to shoot the 55's at 3800 fps., found out you can only push them so fast with a 1-9" twist, that's why I suggested a 1-10 if you have a big enough case. The 1-10 will put less spin on the bullet which equals less stress and a bullet that makes it to the target every time... maybe I got a bad barrel, but it doesn't have any issues with other bullet brands/weights.
Reason for my 20x47 Lapua build was to kill coyotes at long range with out tearing them up, found out it was just a dream.. LOL

There was others that had the same issues as I, they just gave up and re-barreled. I stayed with it but switched to a lighter bullet that would hold up at higher vel.s...

Last edited by Tim Anderson; 05-10-2015 at 05:14 PM.
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