twist rate and bullet length
this is my first post and I hope you all can help a guy out of this dilemma.
I ran across this website with a twist rate calculator. http://kwk.us/twist.html
The barrel company I bought my varmint barrel from steered me in the wrong direction for bullet selection and admitted it. They refered me to this calculator and hopefully will put me in the ball park as far as the right bullet for 1:12 twist .243 winchester. Before I rebarreled my Savage with thier barrel, I was achieving .75 inch groups at 300 yards with a standard 22"sporter barrel. With thier barrel, I am getting 3 inch groups at 300 yards. At 100 yards things are very good, clover leafing.
I tried 55 to 85 grain bullets with at least 5 diffent powders, all tested at 100 yards for the best groups at different velocities. I read that sometimes a bullet doesn't stabalize until later down range and heard a guy once say that his 22-250 tightens up at 300 yards verses 100 yards.
What say you all?
Selecting bullets for twist
Try this site: http://www.jbmballistics.com/cgi-bin/jbmstab-5.1.cgi
I'm working up loads for a 6X47SM varmint rifle with a 1:12 barrel and the 'heaviest' bullet that will fully stabilize with what I was given to work with is the Sierra 75 gr flat base HP. Also a 58 or 65 gr V-Max or 55 gr Nosler BT. nhk
that site is too broad..... the 55 will not stabilize with a 1:12
Here is a link to Shilen barrels chart to twist rates. http://www.shilen.com/calibersAndTwists.html
55 Nosler BT
The .243 diameter 55 gr Nosler BT should stabilize, see attchment. nhk
You can't go by that,"up to 85 grains for 1:12".... That's what McGowen told me too. Bullet weight isn't the way to go to pick a twist rate.
That's to broad of a window.
Originally Posted by nhkuehl
I'm afraid I don't follow you(?) nhk
Originally Posted by shootsteady
the sierra 55BK show it needs 1:14 at 3200 fps.....
the Nosler 55 BT shows it needs 1:13 at 3000 fps..... both based on bullet length and not by weight....
your scale shows...at different velocities that push the twist too far out of wack.
I believe the twists you are showing are based on thr Greenhill or Velocity formulas which are based on the density of lead. The new bullets (Boattails, hollow points, and polymer tips) make a bullet less dense than lead and require more twist. The Don Miller Twist Rule takes that into account and the longer bullets per weight require more twist to stabilize them. nhk
Originally Posted by shootsteady
My 6BR based on a Savage action with a PacNor 1/12 twist will stabilize an 80 gr Berger just fine at about 3100+ fps. I haven't tried anything heavier or longer. Anyway, weight is not the critical factor for a bullet, it is length. I can also tell you that a 1/15 twist 6mm barrel will not stabilize a bullet longer than about 0.800". Except maybe at 5,000 feet altitude or greater.
l just want to know where you got all those Savage's that shoot 3/4 inch at 300yds.
sounds like BS to me...makes you wonder about anything they have to say....
I suggest reading Applied Ballistics For Long Range Shooting by Bryan Litz, copyright 2009. nhk
Originally Posted by Donald
Maybe I'm just denser than average tonight, but I find it hard to believe that a barrel that truly has a 1 in 12 twist won't stabilize a 55 gr Nosler Ballistic Tip. The ones I have measure just under 0.8", about the same as the 58 gr Hornady V-Max. The original .244 Remington had a 1 in 12 twist and generally worked with most standard jacketed bullets of 90 gr or less in weight, but some would stabilize longer and heavier bullets. And yes I know it's length not weight, but 90 gr gilding metal jacketed, lead core spitzer bullets are pretty much the same length except for VLD's &c.
A .243 Win should be easily able to move a 55 gr Ballistic Tip at 3600 fps or way more depending on barrel length. The only problem with most .243 chambers is that they're cut with reamers designed for long bullets, so it's not possible for a relatively short bullet to get anywhere near the rifling. The throats are larger than needed for top accuracy too. Neither of these conditions will give any sort of optimal accuracy. If bullets are the least bit crooked or out of line with the bore and have to make a 0.1" or more jump to the rifling along with high velocity I'd likely be happy to achieve minute of Angus bull's hind end at 100 yards.
The last .243 barrel I had was a 26" Lilja 1 in 12 barrel and it shot 75 gr hollow points, 70 gr Ballistic Tips, 85 gr Sierra HPBT's, and 87 gr Hornady HPBT's well. The shorter bullets wouldn't work because it wasn't possible to seat them anywhere near the rifling.
If your barrel is putting bullets sideways through the target, or missing it completely with a 1 in 12 twist there's something wrong beside the twist. If the twist is way off, try 80 gr Sierra MK's in a 14" twist .222 sometime, bullets will not even hit a target at 25 yards. I'm not sure what twist would be unsatisfactorily slow for the shortest 6 mm bullets that wasn't a special order like a 15 or slower twist. If the problem is poor accuracy, but the bullets are passing through the targets making round holes, it's not the twist of the barrel.
You say that you get cloverleafs at 100 yd and 3" groups at 300 yd. Are you using windflags? if your groups are 1" tall and 3" wide at 300 yards it's likely wind, but wind can cause bullets to go up or down too depending on where it's coming from.
someone with a gift of gab needs to explain what 'minimum twist' means to shootsteady. he thinks a 12 twist is going in the wrong direction to stabilize the bullet.
the 55bk needs 3200 fps to achieve a certain rpm to stabilize in a 14, and it needs 3000fps to reach that rpm to stabilize in a 13 twist. so with a 12 twist it needs even less velicity to reach that rpm to stabilize. therefore it will stabilize very easy. as walt berger once said to me 'you can only get a stable bullet, you cant over stabilize the bullet'.