twist rate and bullet length

S

shootsteady

Member
Hey all,
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
 
55 Nosler BT

The .243 diameter 55 gr Nosler BT should stabilize, see attchment. nhk
 

Attachments

  • 55 nosler BT.GIF
    55 nosler BT.GIF
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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.
 
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.
 
Twist rate

shootsteady said:
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.
Click to expand...

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
 
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.

Donald
 
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....
Jon D.
 
Suggested reading

Donald said:
Anyway, weight is not the critical factor for a bullet, it is length.
Click to expand...

I suggest reading Applied Ballistics For Long Range Shooting by Bryan Litz, copyright 2009. nhk
 
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'.
 
shootsteady said:
Hey all,
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?
Click to expand...

I all say you heard and inferred a whole bunch of BS......

You have NO DILEMMA, your twist will stabilize 55's just fine. In fact there's absolutely no chance of it NOT stabilizing a lead core 55gr bullet, or even any 70 gr.... it's not until 75-80 that you'll be nearing the edge using typical bullets. The website ref'd doesn't "use" weight in the formula because it's covered in the chart of bullet material from lead to steel.

12 is MORE than necessary twist, EXTRA twist for the bullet in question.... the only common bullet I'd worry about would be the Varmint Grenade but this bullet does say "10 twist required" right on the box.

And then you start arguing???? Using phrases like "that's too broad of a window" and "pushing the twist rate out of wack"......

You came here for help.

You got it.

Your ideas are flat out wrong.

Until you can read and understand McCoy, Litz, Vaughn, Rinker et al don't come on here to argue ballistics! It's a waste of everyone's time. :rolleyes:

As is claiming you useta'could shoot 3/4" groups at 300yds with your factory Savage but now your custom barrel shoots 3" groups...... AFTER shooting "cloverleafs" at 100.


????



There could be all sorts of things going on but twist rate isn't one of them.

And "cloverleafs" aren't groups...... it takes 5 shots to make a group. But somehow "cannabis leafs" just doesn't have the same panache with the leaf shooters...???

You owe your barrel maker an apology.

al
 
shootsteady said:
Hey all,
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?
Click to expand...

In some cases initial yaw isn't overcome till some distance down range, then groups at farther out will be tighter in terms of MOA than groupings at closer ranges.
In another situation theres the effect of compensation. If a grouping at closer ranges shows significant vertical spread but little horizontal spread then at some point the variation in velocity/barrel time can result in slower bullets leaving the muzzle on the upwards stroke of barrel vibrations so it effectively increases elevation by a tiny amount.
When the slower bullet that left the bore at a higher angle drops to cross the trajectory cutve of faster bullets that left the muzzle at a lower angle then vertical spread is neutralized and groups at a longer range can actually be tighter in terms of center to center measurement as well as in MOA than groups fired at a closer range..
 
After reading this thread, I think I now have a better understanding of the phrase, "you can't polish a turd". You da man al.

Donald
 
Old Gunner said:
In some cases initial yaw isn't overcome till some distance down range, then groups at farther out will be tighter in terms of MOA than groupings at closer ranges.
Click to expand...

I must point out that this is unproven conjecture. No one including the folks at Aberdeen have ever documented groups getting smaller with yardage. Looks good on paper, ain't true in real life.

Myself and many others have shot through yaw cards, three of the folks here on this board have tried it over acoustic targets, I've built and wired my range specifically to test this over the long-term but my buddy moved away with his Oehler 43 and I've been too cheap to buy another.......but in the end NOBODY ever to the best of my knowledge has documented groups converging with distance. (and yes I do understand the assertion)

The pic in McCoy of the bullet "converging on it's flight path" has caused a lot of unfounded rumor! :D It does "stand to reason" that if a person were to shoot enough groups through two targets sooner or later you'd luck into one which converges..... but so far no one ever has.

Unless you or someone would care to share a cite and enlighten me??? I'm all ears. :) Anecdotal reports of the thousands of folks who can shoot better groups further out need not apply. I'm talking SAME GROUP.

re the convergence of flight paths compensating for different launch angles, I agree that this is true, and documented/explained quite thoroughly, good call. This BTW can be documented on a 300yd range using only yaw cards, pretty easy to test if you've got accurate enough equipment.

al
 
but in the end NOBODY ever to the best of my knowledge has documented groups converging with distance. (and yes I do understand the assertion)
Click to expand...
Doesn't have to converge, only has to diverge less in order to reduce group size by MOA, converging would reduce group size as measured in inches center to center.
The Compensation factor ( a different effect entirely) has been tested and proven , it works far better with some barrel types than others, the SMLE being the best known and most throughly researched.

PS
With the best of modern loads and bullets initial yaw should be negligible, so the effect may be too minute to recognize with some rifles, but this was not and is not always the case.
 
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