Twist Rates

[Bo Diddley]

Old stock with a slow, unfashionable twist rate, and it's best not to mention it in the advert... keep quiet and hope someone new to rifles will buy it without question.

Got new stock on the shelf to sell, with an all singing & dancing fast twist, and it's a good selling point.... so mention it in the first line...

My local gunsmith quoted me an 18-month waiting time for a T3xlite 1-8".223 a couple of years ago... nothing at all to do with ones they had in stock, all being 1-12"...
a quick ring about, and funnily enough, I found a distant shop that could get one in stock within two days

 

[BE Precision]

Having phoned numerous gunsmiths that were advertising .243 Tikka's, none of them knew the figure.
Strange.

Gun shops, not gunsmiths.

 

[Alpine_hunting]

Boring stuff of no real relevance to day to day stalking.
Boat tailed bullets, generally, require a faster twist whereas flat bottomed bullets benefit from a slower twist. The faster any projectile spins the greater the emphasis in respect of dispersion of any bullet misalignment in the bore and bullet imbalance.

Sorry to bore you, two dogs , but you give interesting answers even if bored. What if you found this thread exciting! It is in the firearms and accessories thread and i find it a legit subject.

The boat tail vs flat bottomed bullets is a good factor i think. As of today if we run the stability calculator for any bullet e.g. berger bullets calculator, this difference is not accounted for in the "majic formula" used to tell you how stable your bullet will be in THEORY. So it is theory.

I personally use the calculator to sort out a limited selection of non-lead bullets for the next stalking season. A box is very expensive and i can't test all of them and select the one that groups the best. Some of them were taken out of the list because the calculator said "potentially ustable"e.g. RWS hit in .30.06, barnes ....since i have a 1:11 twist rate.

What can go wrong with not optimal stability? The calculator says for certain ranges of their Sg factor, that the bulet os not optimally stable, meaning "it can still have good groups but the Ballistic coefficient is reduced" and they give a corrected ballisitic coefficient that you can imput to understand the impact on ballistics.

So i guess that at most shooting distances in europe, even a "not optimal" stability factor is not relevant to select the amo. The only plus of the calculator is to check that your bullet, is not Unstable. But i never have found manufactory ammunition in factory rifles that would lie below 1....

So my impression is that those calculators are useful but not the only selection tool. The twist rate debate is not really relevant for most of us shooting hunting distances.

I end up with barrel length and boat tail vs flat bottom as new dimenssions to have to factor in a stability calculator to start having a more "precise" theory.

Very long message, sorry.

I guess if i were hunting these days o wouldn't embark in such discussions!

Good day

 

[Twodogs]

Seemingly lost in either translation and/or the nuances of language usage!
Brian Litz is a recognised authority in such matters and has published much, might be worth a read. Will not help you hunt better but will increase/baffle you with some of the science and witchcraft behind some of the external ballistics issues.
As said of no real relevance to day to day stalking but interesting from a scientific perspective.
Happy hunting.

 

[Tony Morgan]

I have had exactly the same experience in my search for a Tikka T3x 1 in 8 twist .223. Weeks of trawling google through every gun shop, RFD and Website with not a single one stating the twist on their sites.

Tikka T3x has the twist rate stamped on the barrel!

 

[Jelen]

Tikka T3x has the twist rate stamped on the barrel!

I know it does, but no traders show this on their websites, which was what the initial post was about. We shouldn't have to phone 20 dealers to find out.

 

[Heym SR20]

I have used different calculator of stability based on bullet specs, muzzle velocity, twist rate, atmospheric conditions....

My remaining question about all that is whether these calculation should factor in the barrel length?

If my bullet is accelerated during all its travel in the barrell, everything else equal, wouldn't a bullet fired from a 20 in barrel with 1:10 TR have the same stability factor than a bullet fired from a 22 in barrel with a 1:11 TR?

Your ideas on that are welcome.

Spin rate is function of the twist rate of the barrel and velocity.

So just a thought experiment - a 24” long barrel.

At 1 in 12” twist rate at 3,000 fps it spin at 3,000 revs per sec

Drop that to 2,000 fps it will only spin at 2,000 fps.

Improve the twist rate to 1 in 8” it will turn 1 1/3 turns in every foot - ie 3,333 revs per sec at 3,000 fps.

Or drop the velocity down 2,300 fps and still just 3,000 revs per sec.

Longer bullets need faster revs to stabilise- achieved either by velocity or faster twist.