Reply with quote #9
I personally would not go to a faster than 1:7 twist in a Bolt Gun with a Barrel longer than 24" No need to go crazy there.
Only reason to even shoot a 1:6.5 is because of a short Barrel of the service rifle AR15. In Anything longer a 1:7 works just fine as Jerry Pointed out.
And since Mr Thunder is from Australia I doubt he is shooting any Semi auto 20" barrel anything, ( just a guess).
Right Now Jerry is leading the way on this research. You would be well advised to pick his brain on all such matters of shooting 90's out of a Bolt gun at Long Range. He has alot of data on 80's as well. Judging by the amount of data he has collected and charted I would say he is buring up barrels for our digestion of information on the subject.
Jerry where do find all this time to do that??
Reply with quote #10
From several years' experience shooting JLK 90VLDs out of 6.5-tw AR service rifles, I agree with Jerry's assessment of the problems many shooters have had with 90s in the past. My 1st 6.5-tw was a PacNor 3-groove AR SR, and it was absolutely a hammer. The next three 6.5s were not-so-hot, varying from mediocre to a downright disaster that blew up everything I shot through it except S77s. I finally gave up on 90s at about the same time I gave up on 6.5-tw. 223 bbls., in the belief that 90s wouldn't work with anything slower than a 6.5 twist.
However, after reading Jerry's post on LRTargetShooting, I just had to try some left-over 90 ammo through the 7.5-tw PacNor on a M70 - they shot great at 600, and middlin' good at 1000. Haven't shoot enough of the Berger 90 VLDs through this barrel yet to have much of an opinion on them, but there's no doubt that the 7.5-tw is plenty fast enough to stabilize a 90. I'm not getting quite as much velocity as Jerry is, but my bbl. is 27" long.
Reply with quote #11
The Dominion of Canada Rifle Association, Winter/Spring 2008 newsletter, called "The Marksman" has a very extensive article on shooting heavy bullets in the 223 Remington out to 1000 yards. The article on heavy bullets in a 223 begins on page 16 and you need Adobe Reader to view it. Well worth the read!
I have begun testing these loads mentioned and have had very good results, but I am still in load developement. I am using a Savage 12 LRPV with a 1:7 twist barrel that has been massaged by Larry Racine. Hope I am not giving up the secret Holy Grail to 223 loads.
Reply with quote #12
Was shooting with my buddy on our club`s 300 metre range last Spring, getting ready for the ORA F Class season. I was having good luck with 75 gr AMax molys which I was trying for the first time in my MacLennon 30 inch 8 twist barrel.
He was trying 90 gr MKings in a Savage LRPV 7 twist. Can`t remember his load. He would usually put 4 shots into moa but there would be a 5th shot flier. The flier happened at anytime during the firing sequence. Now and then there would only be 4 shots on the paper. After reading the above mentioned DCRA article, we didn`t know if the flier was so wide it missed the paper or if it had blown up before reaching the target. Anyway, he sticks with 80 gr Berger or MKing now.
Reply with quote #13
There is much discussion about bullet stability in relation to the 90gr bullets. It seems everyone is happy with 8 twist for the 80gr bullets as most use this with great accuracy and stability out to maximum ranges.
Lets get technical and do some stability calculations using Bryan Litz's software from his new book. We will look at 2 bullets and 2 twist rates.
Sierra MK 90gr are 1.171" long with a G7 BC of 0.256
Berger VLD 90gr are 1.263" long with a G7 BC of 0.281
Twist rates used will be 7.7 and 7.0
Bryan Litz suggests a stability factor higher than Sg = 1.4 to allow a margin of safety for adequate stability. Anything under Sg = 1.0 is unstable. (Sg is the gyroscopic stability factor)
MV = 2900fps 7.7 twist for a Sg = 1.39
MV = 2900fps 7.0 twist for a Sg = 1.68
Berger VLD Bullet
MV = 2900fps 7.7 twist for a Sg = 1.11
MV = 2900fps 7.0 twist for a Sg = 1.35
MV = 2800fps 7.7 twist for a Sg = 1.38
MV = 2800fps 7.0 twist for a Sg = 1.67
Berger VLD Bullet
MV = 2800fps 7.7 twist for a Sg = 1.10
MV = 2800fps 7.0 twist for a Sg = 1.33
Its interesting to note that the Berger bullet is longer than the Sierra bullet and therefore requires more stabilization (more twist) but has the higher BC.
In the above example the Sierra bullet is better suited to the 7.7 twist barrel and the 7.0 twist only just gets to Bryan's recommended Sg >= 1.4 for both bullets.
Using Bryan Litz's "Point Mass Ballistics Solver" software has given a better insight into how to determine the stabilty needed for the 223R 90gr high BC bullets. Now I just have to go out and shoot it and find out for myself how well my choice of 7 twist barrel will perform!
Edit: I just found JBM now have a stability calculator, do your own calculations here: http://www.jbmballistics.com/~jbm/cgi-bin/jbmstab-5.0.cgi
Reply with quote #14
Since reading the Litz book and seeing how high the BC of the 90gr Berger VLD's are, I decided to see what would happen in a 8 twist Shilen 223 at 22" long.
Using a standard 223 chamber, the VLD is seated well into the case. Kind of looks neat cause only the point is sticking out.
Not expecting much, I made up a couple of loads based on what I am using with 80gr Amax and Varget.
One load put 2 shots 1/4" apart in gusty winds (only shot 2rds cause was expecting them to go in sideways). All holes nice and round.
So I loaded up a some more of this load and headed out to 1035yds (swarovski LRS). Temp around 7C, elevation approx 3000ft.
NO issue making this distance at a chronied speed of only 2600fps. Bullets did land with good accuracy (plinking at rocks).
Out to 1175yds, no problem at all. Bullets dropping into a target about the size of a milk jug.
Again, only a few rds fired at each distance cause I was fully expecting the bullets to tumble.
I am very surprised but this bullet handles the 8 twist just fine and is very easy to set up. It is well off the lands and is working just fine.
Very interested in how this will work as either an F T/R in 223 or as a 22/250 in F Open.
Reply with quote #15
Interesting post Jerry!
I just ran 2600fps with the Berger 90gr VLDs thru the calculator with an 8 twist barrel and the result was 0.99Sg, which is borderline stable.
I shot a few Sierra 90gr thru my 8 twist 30" barrel at 2722fps and got pretty good accuracy. I am going to load it up a bit and maybe get around 2850-2900fps and see how it performs.
Reply with quote #16
Agreed, the numbers certainly do not support the type of performance the bullet did at 1200yds.
As time allows, I will try shooting some more and try to get a feeling for the accuracy of this set up.
I wonder if some of the problems some shooters have reported could be due in part by too much spin/stability.
Still lots to try.