14" Twist - How Heavy A Bullet Will It Stabilize?

R

rcw3

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I have a 14" twist 6mm barrel, and I am wondering how heavy a bullet you can run accurately and it will stabilize.

65 gr. bullets? Yes or no?

Robert
 
Stability for any given twist is based upon more than bullet weight. Bullet length and temperature have a profound effect also. The most commonly used 68 grain bullets are made with .825 jackets and will make bullets of about .840 finished length, depending on dies and base configuration. They will stabilize in a 14 twist as long as the temperature of the atmosphere is not too low. If it gets down around 40 degrees or so you may start to see more fliers and bad groups. Then you could go to a shorter bullet of about 65 grains on the .790 jacket. The rule of thumb is, a heavier bullet of the same length will be more stabil than a lighter one, a shorter bullet of the same weight will be more stable and higher temperatures will improve stability everything else being equal.
 
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LARRY FEUSSE said:
Stability for any given twist is based upon more than bullet weight. Bullet length and temperature have a profound effect also. The most commonly used 68 grain bullets are made with .825 jackets and will make bullets of about .840 finished length, depending on dies and base configuration. They will stabilize in a 14 twist as long as the temperature of the atmosphere is not too low. If it gets down around 40 degrees or so you may start to see more fliers and bad groups. Then you could go to a shorter bullet of about 65 grains on the .790 jacket. The rule of thumb is, a heavier bullet of the same length will be more stabil than a lighter one, a shorter bullet of the same weight will be more stable and higher temperatures will improve stability everything else being equal.
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thank your for your post! You answered a question I've long had about flyers in 40 degree temps. Is this why many guys shooting 30BR's goto a 1:16 twist when it's cold outside?
gary
 
Squeakie, not to be argumentative, but there is not a 68 grn Match Bullet built on a .825 jacket that a 1-14 twist will not stabilize in any temperature, or condition. That combination has been the standard for short range Benchrest for decades. They will shoot just as well at 30 degrees as they do 90, if the tune is right.

As a note, I loaded up some 80 grn Sierra Varminters, which are rather short, in one of my 1-14 6PPC 's at about 2800, and they shot quite well, about .500 average..........jackie
 
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I'm with Larry on this one,
30deg is "sultry" around here in the winter. We sometimes shoot to 5 below. Stability issues with 14 twist 6ppc barrels and .825s are obvious in the colder temps. .790's fix everything. Interesting part of this subject is that I have seen .825's go "stupid" in cold temps but I have not seen .790's go "stupid" in hot temps----------comment's ?---------Larry,you out there ?
Joel
 
LARRY FEUSSE said:
Stability for any given twist is based upon more than bullet weight. ........ stable and higher temperatures will improve stability everything else being equal.
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Larry, PM me and give me your email address. I need to ask you something about Dublin and the phone # I have for you from last year in Kansas seems to not work.
 
I guess I "opened Pandora's box" by asking an overly simplistic question of barrel twist and what bullets would be stabilized. The answers are great and give me a better perspective of the issues. It seems that many of the bullets in the mid 60's may stabilize fine with a 14 twist as long as they are not particularly long. I guess the only way to really determine this is to try out different bullets and see.
Thanks!

Robert
 
Jerry, my email address is lrfeusse@hotmail.com .

Jackie, I agree that a 68 grain bullet may work well down to 30 degrees, but I was trying to give a safe answer to the question, one that would nearly guarantee a good result for the questioner. Other factors that may have lesser effects, but may tip the scale by a few degrees in either direction are atmospheric pressure (altitude) and also the base configuration (flat base tends to be more stable). Also some barrels may not be exactly the twist that is intended, especially button rifled barrels may come out as 14.15 or maybe down to 13.8 or so, which could give a change in stability of a few more degrees in temp. The best barrel I ever had was an advertised 15 twist that turned out to be 14.65. The best it ever shot was with 66 gr. FB bullets on .825 jackets at about 70 degrees. Tony said I would never get another barrel that good, and he has been right so far.
 
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LARRY FEUSSE said:
Jerry, my email address is lrfeusse@hotmail.com .

Jackie, I agree that a 68 grain bullet may work well down to 30 degrees, .
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Thanks Larry.

And, guys remember the effects of atmospheric condidions on bullet stability, are not only temprature but also dew point and barometric pressure. These elements create a condition we pilots measure and call Density Altitude, or simply put, air thickness.
 
I have shot the 70 Gr Sierra in some of the coldest temperature ever recorded in the month of September here in Austin without any issues
as well as the 68 gr cheek 00 BT in the same conditions with no problems using a 1/14 Shilen.
I would put the temperatures at well below 20 degrees.......celcius.
Ted
 
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alinwa: The Nosler 70 gr. BT's are .910 long. Assuming 3400 fps and twisted 1:14 at 10 degrees C....the s.g. numbers are in the .820's.
 
TedH said:
I have shot the 70 Gr Sierra in some of the coldest temperature ever recorded in the month of September here in Austin without any issues
as well as the 68 gr cheek 00 BT in the same conditions with no problems using a 1/14 Shilen.
I would put the temperatures at well below 20 degrees.......celcius.
Ted
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20C is 68F.
 
This I know for a fact. Years ago, I bought a 1-15 twist barrel. At that time, I was shooting 68 grn Fowlers, (825 jackets), out of a 1-14. That 1-15 keyholed every bullet, many did not even hit paper.

This was perplexing, since quite a few shooters shot Fowlers in a 1-15. I had some 65 grn Watsons on .790 jackets, and they shot pretty good out of the barrel. That made sense, the shorter jacket accounted for the stability.

But, why wouldn't this 1-15 shoot the .825 jacket bullets. Well, we finally checked the actual twist on the barrel, and it was more like 15.5 in 1 than 15. That little bit more, (or lack of), twist was enough to send things south.

That did show that we were right on the edge with a 1-15 twist and a standard 68 grn Benchrest Bullet built on .825 jackets.


The only other time I ever keyholed a bullet was back when I shot a 25BR. I usually shot 85 grn Fowlers on a .925 jacket out of a 1-13 twist. On a whim, I decided to see if I could make that Berger 115 grn 25 caliber VLD shoot. The shots that did hit paper cut about 1 inch slots........jackie
 
rcw3-I recently converted a Cooper 6PPC to a 6 Dasher but kept the seldom shot barrel to save a few $. It is a 14 twist and I just shot a .35 group with 4895 and Sierre 70g MK's at 100yds. Coldest temp I've shot is about 48-50 deg. This gun is hell on Pd's and soon coyotes. Hope this is helpful. V/R Greg
 
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