Why not 1/8 twist?

[Obscenejesster]

You are only looking at a slice of their data. Sierra tested many bullets using the scientific method and they know how to get accurate and reliable data.

The end result is that they saw a difference in accuracy between the 1:7 twist and the 1:8. It may have been small, smaller than average shooter would be concerned with, but a difference nonetheless, a difference that a match shooter might be concerned with at 600 yards, especially if a bullet longer than the 69 gr SMK is being used.

You're making it sound like Sierra's testing found that 1/7 was more accurate with every bullet they produce for .223 when you say "especially 69gr and above". I've never seen any data from Sierra stating that. In fact, they would never state that. They know that every barrel is different. Different rifling, different material, different bore etc......We only saw testing done with a particular load, barrel and bolt action rifle at 100 yards. The only information I've ever seen Sierra state is what twists will and will not stabilize a particular round. After efficient stabilization, the rest is dependent on barrel and load.

Lets take their 80gr Matchkings for example. They specifically note "This bullet requires a 1x7" to 1x8" twist barrel." They don't specify what twist is going to make it more accurate because they know there is so many other factors coming into play.

I don't even know how this thread evolved into a topic of Sierra bullets and I don't even know why you are fixated on a particular manufacture.

Bottom line. Certain 1/7 barrels will be more accurate with certain 69gr rounds and certain 1/8 barrels will be more accurate with certain 69gr rounds. All things being completely 100% equal, a 1/7 barrel should be more accurate with bullets above 79gr and a 1/8 should be more accurate with bullets below 62gr.

[markm]

blah, blah, blah....

saying the degree of boat tail doesn't effect accuracy, transonic and beyond, is .. ah .. silly.

We've experienced this first hand. Didn't know it at the time, but we shot some 168gr Noslers that fanned out BAD at 975 yards. They don't handle transonic for shit. I'm talking landing anywhere in a 12 foot circle at that distance with very little side wind.

Those bullets are still gathering dust on my shelf.

[markm]

Lets take their 80gr Matchkings for example. They specifically note "This bullet requires a 1x7" to 1x8" twist barrel." They don't specify what twist is going to make it more accurate because they know there is so many other factors coming into play.

Case in point... we have a 1/9 that we'vs shot those 80s to 975 yards with not stabilization problems.

[CC556]

We've experienced this first hand. Didn't know it at the time, but we shot some 168gr Noslers that fanned out BAD at 975 yards. They don't handle transonic for shit. I'm talking landing anywhere in a 12 foot circle at that distance with very little side wind.

Those bullets are still gathering dust on my shelf.

That's actually addressed in the link I posted above:

It is this effect that has led to the common advice of “Don’t use 168gr 30-caliber bullets at 1000 yards”. That is misleading advice as it resulted from use of the 168gr Sierra ‘International’ (aka MatchKing) bullet with its 13-deg BT angle. (This was, originally, a specialized 300m design — there are various near copies on the market from Speer, Hornady and Nosler.)

[MistWolf]

A slice of their data? It's all that's presented. There is nothing definitive about it. Do you have access to data that isn't available to the public?

Again, the difference is negligible...any statistician could tell you. Especially since it's 10 vs 12 rounds. Furthermore, it's just as likely the load try used was simply better suited for that particular test barrel.

If there is more data, please present it. If you have none, then quit trying to hide behind an unsubstantiated claim that a statistically insignificant, unscientific test within a small set of circumstances is some kind of validation of your claim

CRITICAL THINKING TIME- The article published is only a small portion of the data Sierra has collected. You can bet much of it is considered proprietary. Sierra has been collecting data for decades and it's good enough for Sierra's statisticians to draw informed conclusions.

I'm not here to tell anyone what to think. I present my conclusions based on data and experience. I compare my conclusions to other, trusted sources. It's a process that answers many questions and raises many more. The data shows a measurable degradation in performance of the 69 gr SMK when going from the 1:8 twist to the 1:9. It also shows a measurable degradation of accuracy between the 1:7 & 1:8. From this data, we can draw the conclusion that the 69 gr SMK performs better with the 1:7 & 1:8 than it does the 1:9, a conclusion Sierra agrees with.

We know longer bullets perform better with tighter twists. The Barnes 70 gr TSX is longer than the Sierra 69 gr SMK. The conclusion is that the 70 gr TSX will be less stable from a 1:8 twist than the 69 gr SMK. As we are seeing a degradation of performance with the 69 gr SMK with any twist slower than the 1:8, we can conclude the same will be true for the 70 gr TSX. This supports the observation that the 70 gr TSX will be barely stabilized by the 1:8.

We also know there are variables. Each barrel is a law unto itself. We have all heard stories of a 1:9 barrel accurately shooting bullets long enough that conventional wisdom would have them coming out of the barrel sideways. We've also heard stories of tight twist barrels getting best accuracy with really short bullets. But both are anomalies. We also know that the data presented by Sierra was taken under controlled conditions. Introduce real world variables and it will change and usually for the worse. A bullet that's stabilized just enough can unstable enough to not meet the mission, while a bullet that's solidly stable will merely become barely stable under the same circumstances.

I can't dump decades of experience and knowledge into your head, especially if you're simply going to raise the BS flag at every turn. I can only share what I know and how it applies to me. Now, it's up to you to take my conclusions and test them for yourself. If it turns out that the 1:8 or even 1:14 will stabilize a Barnes 70 gr TSX well enough for your use, then all well & good. But you'll never know unless you actually test it. Whether or not the difference is enough to matter to you is subjective. That does not change the fact it exists.

Your claim that Sierra's data collection methods are a "statistically insignificant, unscientific test within a small set of circumstances" is, quite frankly, laughable

[Obscenejesster]

We know longer bullets perform better with tighter twists. The Barnes 70 gr TSX is longer than the Sierra 69 gr SMK. The conclusion is that the 70 gr TSX will be less stable from a 1:8 twist than the 69 gr SMK. As we are seeing a degradation of performance with the 69 gr SMK with any twist slower than the 1:8, we can conclude the same will be true for the 70 gr TSX. This supports the observation that the 70 gr TSX will be barely stabilized by the 1:8.

Again, I don't know what your fixation is with comparing a single bullet and using it as a basis for all twist rates.

Going by what you just said, if we can assume all 69gr bullets are more stable and accurate being shot from a 1/7 barrel, then we can just all assume shorter bullets 62gr and below are more accurate and better stabilized being shot from a slower twist barrel like a 1/8.

[tylerw02]

I said I was done with this thread, but I'm going to make one more post. First you made remarks of higher BC, which in fact was not the case, then you speak of accuracy, which again, is not the case. 10 rounds in a given experiment vs 12 rounds being .3% larger is not a significant change. Maybe Sierra has more data, but they have not published it. You're making assumptions.

WHERE DID SIERRA SAY 1:7 IS MORE ACCURATE WITH THE 69 GR BULLET OTHER THAN WITHIN THE SCOPE OF A SINGLE TEST?

They have not done so. This test was 10 rounds with a 1:7", 12 rounds with a 1:8". This was with one specific load loaded to achieve a velocity in a test barrel. For pete's sake, shooting 12 rounds vs 10 rounds is enough that you SHOULD see worse accuracy with the barrel fired more. If you'd shoot them 100 times, you'd see even more dispersion. If you draw conclusions other than that this demonstrates the reason for various twists, then you're naive at best.

You cannot conclude anything about a different bullet because of this test. You are concluding something with no data, no experimentation, all based on an assumption. By the way, there is more to making a bullet stable than twist rate or length of bullet. If you want to make a comparison of the 70 gr TSX in 1:7" and 1:8", then actually find some data rather than drawing a conclusion. You may indeed be right, but you have no evidence to suggest such.

I could conduct the same non-definitive test as the quoted test, with a 1:7" barrel and show it more accurate than a 1:8", then change the load every so slightly to tune it for the 1:8" vs the 1:7" and then, according to your logic, the TREND would be 1:8" twists are more accurate. My own personal experiment with the 69 gr Sierra in Black Hills ammo suggested of my three or four guns I tried it in, the most accurate was a 1:9" non-chromed Wilson barrel with irons outshoot a 6920, an 18" 1:8" WOA with a 4.5-14x Zeiss, and a CMMG with an Aimpoint. I am not drawing conclusions that aren't there like you are with this Sierra data.

IF YOUR LOGIC IS INDEED WHAT WE SHOULD ALL FOLLOW, WE SHOULD BE HAVING THE DEBATE BETWEEN 1:1" TWIST, 1:4", 1:6"...WHERE IS THE LINE?


Again, stop spreading misinformation. Sierra doesn't say the trend for shooting 69 gr bullets is that 1:7" is more accurate than 1:8". They don't say anything other than to suggest 1:10" or faster. They don't offer more data, they don't allude to further testing than the one which they presented. You are falling victim to confirmation bias. They simply demonstrate that twist rate has a slight effect on ballistic coefficient and that with their set of proofs and that specific lot of ammunition, which barrels were more accurate.


From Sierra:
Designed for Service Rifle competition in the M16A2/AR-15A2, our 22 caliber bullets have set an incredible number of new national records. This bullet is well known for its excellent accuracy at 200 and 300 yards, but it requires a rifling twist rate not slower than 1x10".

[markm]

We know longer bullets perform better with tighter twists. The Barnes 70 gr TSX is longer than the Sierra 69 gr SMK. The conclusion is that the 70 gr TSX will be less stable from a 1:8 twist than the 69 gr SMK. As we are seeing a degradation of performance with the 69 gr SMK with any twist slower than the 1:8, we can conclude the same will be true for the 70 gr TSX. This supports the observation that the 70 gr TSX will be barely stabilized by the 1:8.

Isn't stability an absolute state. A bullet is either stabile or it isn't. No? There is no "more stabile" or "too stabile"...

[CC556]

Isn't stability an absolute state. A bullet is either stabile or it isn't. No? There is no "more stabile" or "too stabile"...

Since the bullet loses forward velocity faster than it loses rotational speed it will become more stable as it flies (assuming it was stable when it exited the muzzle)... until it hits the transonic speeds. At that point a bullet that transitions poorly can become unstable. The perfect example here is the 168SMK. So, other than a bullet that is upset at transonic speeds the answer is "yes, stable is stable."

[markm]

I did a facinating stability experiment not too long ago where I'd have lost the bet if I'd put money on the outcome. Switch to 30 cal mode for a second.... I got some 220 gr soft point bullets with a B.C. that was so poor, you'd not bother shooting them very far at all. So I tried to make subsonics out of them with my 12 twist barrel.

They shot 8 MOA and were yawing when the passed through the paper at 100 yards. For the hell of it, I loaded them to full power, and behold. They were stabile and shot 1 MOA or so. I'd have guess that the increased RPM would be about offset by the increase wind resistance, but not even close. They shot stabile.