Why not 1/8 twist?

[Obscenejesster]

I did a search online and found the Sierra data
http://www.exteriorballistics.com/eb...ned/5th/25.cfm



For a clearer understanding, read the whole article

I just read it and here's what I gathered from it. That particular round (69gr SMK) loaded to it's max (2800 fps) with that particular barrel is on average 17 thousands of an inch more accurate when shot from a 1/7 barrel rather than a 1/8 barrel? Got it.

It's all relevant. This is a particular bullet shot from a particular barrel. There's probably some 77gr bullets that are more accurate when shot out of a 1/8 just like there is probably some 62gr bullets that are more accurate when shot using a 1/9.

[tylerw02]

To take the data to heart, you've got to assume lots of things unaccounted for. The whole read isn't very definitive. It is a limited scope demonstration at best.


Sent from my iPhone using Tapatalk

[Obscenejesster]

While most match grade barrels we're familiar with on this site might be 1:8, I think of you look at true match barrels, you'll probably find most are 1:7. Yes, there is a difference between a match barrel and match grade barrel.

Seriously??? Where can I find me one of these "True Match Barrels"?

[markm]

How about National Match barrels?

[CC556]

To take the data to heart, you've got to assume lots of things unaccounted for. The whole read isn't very definitive. It is a limited scope demonstration at best.


Sent from my iPhone using Tapatalk

Not to mention it's all done at relatively close range where these effects they talk about are minimized to the point that other factors can easily mask what they're looking for. And it's just a sample of 10 rounds through each of two different barrels. Such a small sample size, at such short range, producing numbers so similar, and not being able to account for other variables (though they at least mention them) really doesn't leave us with much to hang our hats on other than the most basic (and really uncontested point) that you should pick a twist rate suited to the bullet you want to fire if you're going for maximum accuracy.

[MistWolf]

To take the data to heart, you've got to assume lots of things unaccounted for. The whole read isn't very definitive. It is a limited scope demonstration at best.

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.

Boat tails reduce drag at any speed, not just when transonic. Think of even large things in everyday life like actual boats, lots of passenger cars, those semi-trucks with trailers sporting those cone-looking things on the back, etc... They all use a "boat tail" design to lower drag at velocities far less than transonic. Just as with the boat tail bullets, such a shape reduces drag at all velocities.

The area of the back trucks and such is much larger than bullets. Ballistic testing has shown BTs don't affect bullet drag to any practical degree. The biggest affect of the BT is to reduce turbulence in the transonic range

Also, "real" match barrels have a twist rate suited to the particular bullet being fired. There's no advantage to over-spinning the bullet but there are real-world downsides. Look at something in .224" diameter like a 22PPC and you'll find the "real" match barrels will be 12 or 14 twist since that's all they need for the bullets they shoot. If you're single-loading an AR and shooting the 80-90gr bullets you might find in some match formats you'll probably use something like a 7 twist but don't think that all "real" match barrels are such a fast twist.

You are correct. I should have made it clear I was talking about service rifle competition. If you go to the highpower rifle forums, you'll see 1:7 is popular

I just read it and here's what I gathered from it. That particular round (69gr SMK) loaded to it's max (2800 fps) with that particular barrel is on average 17 thousands of an inch more accurate when shot from a 1/7 barrel rather than a 1/8 barrel? Got it.

It's all relevant. This is a particular bullet shot from a particular barrel. There's probably some 77gr bullets that are more accurate when shot out of a 1/8 just like there is probably some 62gr bullets that are more accurate when shot using a 1/9.

That is quite true. Each barrel is a law unto itself. But the trend is, 1:7 works better for longer bullets. The key word is trend. That's why you have to get out and actually shoot. I have a 20" 1:8 Lothar Walther barrel that shoots 77 gr bullets very well. I also don't shoot at a level where I personally would see a difference.

T2C experiences show that the 1:8 works well for him. Another member (forget his call sign) has experience that the 1:7 consistently works better than the 1:8

Seriously??? Where can I find me one of these "True Match Barrels"?

Ok, shoot me for throwing in the "true". I was trying to differentiate between a "Match Grade" barrel and a "Match" barrel in my writing. Makers of match barrels will tell you there is a difference between "Match" barrels (what I called a "true match") and a "Match Grade". Match barrels are held to a higher level of QC/QA and consistently shoot more accurately than match grade barrels

[tylerw02]

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.







Sent from my iPhone using Tapatalk

[CC556]

The area of the back trucks and such is much larger than bullets. Ballistic testing has shown BTs don't affect bullet drag to any practical degree. The biggest affect of the BT is to reduce turbulence in the transonic range

Do you have a link to some data? I'm having a hard time believing that in an application where even tiny changes to the ogive shape or meplat diameter make a significant difference the presence or absence of a boat tail would make no practical difference.

This touches on it a bit:

http://bulletin.accurateshooter.com/...-and-accuracy/

Bryan Litz says the ideal boat-tail angle is 7-9°. Go much above 10° and it’s too steep for the air to follow the bullet sides around to the base. This seems to manifest itself as much increased drag and turbulence leading to instability in transonic flight.

The boat tail reduces drag and turbulence, which helps keep the bullet stable as it goes transonic. It doesn't only help at transonic speeds, it helps all the time and helps as the bullet hits that transonic range. As you can see in the pic below from the article, the turbulent area behind the bullet is made smaller by the boat tail. The end of the boat tail is basically the flat base, and with a proper tail angle the effective size of that base is reduced compared to a bullet with no boat tail and a flat base (and resulting area of turbulence) that is much larger.

[CC556]

blah, blah, blah....

saying the degree of boat tail doesn't effect accuracy, transonic and beyond, is .. ah .. silly. Turbulence causes off axis spin, off axis spin causes increases drag, and a not consistent drag curve.. across the DA

Are you taking issue with what I said, or what the other guy said? The link I provided specifically states that the angle of the BT does matter and the effect in reducing drag and turbulence benefits the bullet.

[tylerw02]

Ok, shoot me for throwing in the "true". I was trying to differentiate between a "Match Grade" barrel and a "Match" barrel in my writing. Makers of match barrels will tell you there is a difference between "Match" barrels (what I called a "true match") and a "Match Grade". Match barrels are held to a higher level of QC/QA and consistently shoot more accurately than match grade barrels

Really? Krieger and Bartlein and all the rest have different levels of QC/QA for a barrel given status of "match" and "match grade"?

I can't find anything on any of the barrel makers' pages other than Shilen who has two lines for barrels, "match" and "select match" where the select are the barrels that air gauged to a better uniformity than their "match", but no better than any of the other companies barrels.

The reality is the end user is the one that determines what a match barrel is, as he or she is the ultimate certification of quality. No matter how good the specs and gauging is on a barrel, sometimes your "match barrel" can't be your match barrel because it fails to delivery the accuracy and precision necessary for the task at hand. If you've never spent $700 on a barrel and have it fail to perform, despite spending the time and money with a reputable smith, developing a load, using the right bullets for given twist, and putting your time on it you simply wouldn't understand how asinine your statement is. Its not like there is a shelf in the back of the building where real match barrels come from while the riff-raff gets junk.


ETA:

I'm done with this thread. Nobody is going to present anything useful, we're not helping OP determine that he is or isn't giving anything up for his needs at this point by going 1:8" next time.