Twist rate vs bullet weight?
- Thread starter sgt_jamez
- Start date
With the lighter weight bullets you don't need to worry about stabilization in a 1:8 twist unless you are running super hot loads and the bullets break apart (can that happen in a 6br???).
To put it another way, if you had a 1:13 or 14 twist you would be able to shoot the typical 6mm bullets in benchrest competition i.e. 66-68gr, but you would not be able to shoot the 105's. A 1:8 twist will shoot the 105's and also be able to shoot the 68's, but you may not get the same accuracy with the 68's in the 1:8 as you would if you had the 1:13...or you will and that would be awesome, but you shouldn't have to worry about stabilizing them.
I have a 223 with a 1:9 that will shoot 69gr as well as 52's, but I know I could never get the 69's to shoot in a 1:14 that the 52's are perfect for.
Hope this helps,
Mike
To put it another way, if you had a 1:13 or 14 twist you would be able to shoot the typical 6mm bullets in benchrest competition i.e. 66-68gr, but you would not be able to shoot the 105's. A 1:8 twist will shoot the 105's and also be able to shoot the 68's, but you may not get the same accuracy with the 68's in the 1:8 as you would if you had the 1:13...or you will and that would be awesome, but you shouldn't have to worry about stabilizing them.
I have a 223 with a 1:9 that will shoot 69gr as well as 52's, but I know I could never get the 69's to shoot in a 1:14 that the 52's are perfect for.
Hope this helps,
Mike
MilGunsmith
Member
You can also reduce your velocity if you are having accuracy problems with the lighter bullets. The bullet stability is based on the bullets rotational speed, which is controlled by the velocity and he twist. You have control over the velocity.
You've been given solid information.
1:8 will stabilize any bullet you're likely to run across, and definitely all lighter bullets.
The rule is, you increase the twist as you increase the length (weight)
Therefore a 1:14 twist will stabilize _most_ bullets up to 70gr but large bullets will tumble
1:12 allows you to go up to most 85gr
1:8 allows you to go all the way up to encompass most commercial length bullets..... including the Berger 115 for instance.
The REALLY long 6mm bullets like Don Lahr's 125's require 1:7
"Over-stabilization" is wildly hyped in books and on the innertube with some sites even claiming "over-stabilized bullets fly nose high" and precess/nutate uncontrollably and refuse to go to sleep nor to nose over at the top of their trajectory" and blahh and blahh and blahhhh
This is all Krapp from folks trying to be relevant. And attempting to explain why their "accurate" guns won't print small groups at 100yds. This attempt at relevancy has allowed an entire industry to be built around the idea that some setups "shoot better" or are "more accurate" at distance.
It's true that theoretically an over-spun bullet "should be less accurate" due to bullet imbalance but in the real world I've yet to actually feel a difference between twist rates. GOOD bullets, accurate bullets will be accurate thru anything.......And I've fired thousands of wee BR bullets thru 8" twists. The effect of the extreme rotation on varmints is startling.
I have blown up a lot of bullets but not many in 6BR's and in any case I've NEVER blown up a Nosler Ballistic Tip even when pushing the liddle 55's to over 4000fps
Try it, I think you'll like it
There are plenty of people on this site who make actual Benchrest Bullets, even the guys who make the dies for making these extreme bullets are here..... guys who actually UNDERSTAND bullet stability (if a guy named R.G.Robinett answers your post, take it to the bank
or George Ulrich)This really is a fascinating and poorly understood subject and only on this single shooting site can you access the true ANSWERS versus a bunch of unfounded opinions.
AND, BTW, if in your travels you run acros't one of them "bullets going to sleep" guys, remind them that some goinker named alinwa will buy his airfare, pay him 1000.00 and buy him a steak at Ruth's Chris if he's willing to come over and do it for the record.....and proves that he CAN shoot smaller at distance because his 1:8 twist is somehow "over-stabilizing" his bullets.
Even with them there "too light bullets"
MilGunsmith
Member
We do this testing everyday and can see the bullets pitch and yaw. By varying the velocity or twist rate we can make the bullet "go to sleep" We are using a Sydor Technologies Y.A.W. (Yaw Analytics Workstation) to take pictures of bullets in flight from multiple angles at various distances. https://sydortechnologies.com/ballistic-impact-testing/external-ballistics/
Of course bullets pitch, yaw, nutate and even "go to sleep" but what they DO NOT DO is print tighter groups after falling asleep.
This, and only this is what my bet addresses, the idea that "some guns group tighter at 600 than at 100"
Nor do "over-stabilized" bullets fail to tip over to follow trajectory.
MilGunsmith
Member
Then please explain why we have documented proof of rifles that shoot 1/2 moa at 600 yards shooting larger groups at 100. Our M14NM rifles would shoot tight 1/2 moa groups with 168gr SMK at 600 using 41.5gr of IMR4895, but to get them to shoot 1/2 moa at 100 we used 39gr of IMR 4895.
Nothing to explain.... the fact that one gun or load shoots better at a given yardage is meaningless Nearly everyone in every discipline around the globe has been tailoring different loads for different yardages since The Dawn Of Accuracy, leading folks everywhere to assume that somehow these groups are converging.
Unless you're measuring the same group(s) at two different points and when you overlay them the second group is tighter, NOTHING is established. Except that you like this load better for this yardage.
I own 2 Oehler 43 setups. Using these you measure groups twice, once at 40-100yds and then a paper target at 300-350-500-600...... pick your poison.
"Documented proof" gets thrown around and used to sell junk every day.... If I write in my diary "I Pooped Today" I now have "documented proof for all time.
Doesn't explain anything, but it "proves" to most folks that I had a movement!
Gene Poole
New member
So you're saying that if you, say, put a cellophane sheet at 100 and a target at 600, the MOA size on the cellophane would be larger than the MOA size at the target?
Butch Lambert
Active member
A group regardless of size at 100 yards will not be smaller at 600 in MOA. I do believe with different circumstances like load, bullets, and other things will tighten up the MOA at 600, but it will not be larger in MOA a 100.
Bullets do not converge on each other as they go downrange.
Bullets do not converge on each other as they go downrange.
Whether MilGunsmith admits it or not, others DO say that, and YES that is exactly the contention and exactly what I'm combating. I've had a tall target using onion-skin paper to shoot thru for years and folks say "well, the first paper disrupted the bullet"
Now I have acoustics, the first target is air......
I don’t think that is exactly what they mean Butch..The best tune for 600 usually isn’t the best tune for 100.
I would think in short range game some might have a different load for 200 and 100. So your best 200 yard load might not group as good at 100.. On my 600 yard gun I usually have to tweak my best load at 100 for best tune at 600. I personally believe there is something to positive compensation. But have no proof just what I have seen in my experience.
I live daily using positive compensation. In my life a load tuned flat at 200 will most likely be miserable at 600, I too am a believer, have been for 20yrs BUT, this is simply NOT the contention.
Gale McMillan is the first guy I know who "validated" this convergence theory in public, as a professional figure, and he'd never heard of positive compensation.
I think anyone who actually shoots good equipment to good effect will agree on 100 VS 200 VS 600yd loads as to them being different. Even in the short-range game it's been common knowledge that if you're gonna' only tune at one yardage, tune at 200 instead of 100, elstewise you're headed for a trainwreck.
This decision has been based on something called "empirical evidence" (read TRAINWRECKS!)
LOL
Gale McMillan is the first guy I know who "validated" this convergence theory in public, as a professional figure, and he'd never heard of positive compensation.
I think anyone who actually shoots good equipment to good effect will agree on 100 VS 200 VS 600yd loads as to them being different. Even in the short-range game it's been common knowledge that if you're gonna' only tune at one yardage, tune at 200 instead of 100, elstewise you're headed for a trainwreck.
This decision has been based on something called "empirical evidence" (read TRAINWRECKS!)
LOL
MilGunsmith
Member
We track bullets with Doppler radar, multiple acoustical targets, Oheler chronographs, and the Sydor system. Bullets do all sorts of interesting things when fired.
rkittine
New member
Although I have limited experience, reading about this issue, I have found articles that do claim that as certain projectiles stabalize, they spiral into a tighter group as they go down range, but my experience is that say a projectile that will hold 1/4 MOA at 100 yards may only hold 2 MOA by the time it gets to 300 yards, but that a projectile that is better suited for longer range, may only hold 1/2 MOA at 100 and still be only slightly increased at much longer yardages.
OK, let's keep it real simple instead of "bullets do all sorts of interesting things"...... DO YOU have documented instances where groups converge? DO YOU have documentation showing where groups actually get smaller with distance? THE SAME BULLETS in THE SAME GROUP not some "we load differently for 100 than for 600?"
This is the only question on the table and you seem qualified to make a statement. Could you win my bet?
geo.ulrich
Member
I believe Bob is referring to the "coning effect", there seems to be some validity to it although I have not seen it shooting through multiple targets out to 300 yds
Pete Wass
Well-known member
Just for the heck of it
I did my last load testing on the 50 YD Rimfire range at the club. I found a single bullet hole group. I've been shooting the same loaded round parameters at 1-2 and 300 yds all season and have shot some tiny knots @ 300 with the rifle and it's ammo. Like teen groups, figured by MOA.
I shoot HBR rifles so can't see much in the way of shot placement as I go. I shot the most xes I've ever shot @ 200 the other weekend with that ammo.
SO, I think, for my purposes, my 50 yd parameter ammo works good enough.
Pete
I did my last load testing on the 50 YD Rimfire range at the club. I found a single bullet hole group. I've been shooting the same loaded round parameters at 1-2 and 300 yds all season and have shot some tiny knots @ 300 with the rifle and it's ammo. Like teen groups, figured by MOA.
I shoot HBR rifles so can't see much in the way of shot placement as I go. I shot the most xes I've ever shot @ 200 the other weekend with that ammo.
SO, I think, for my purposes, my 50 yd parameter ammo works good enough.
Pete
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Butch Lambert
Active member
What do they mean then? I'm saying that your best load for 50yds, 100yds, and so on will not make bullets converge in an smaller group down range.