What exectly do the different barrel twist rates do for performance?

My first useful tech forum post
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www.ammo-oracle.com

Please do a search.  That subject has been beaten to death numerous times already.

Quoted: Please do a search.  That subject has been beaten to death numerous times already.

Sorry to bore you with my ignorance ......Obviously this is what my search returned -No Topics Found......or I wouldn't be asking ........Thanks

Quoted: Sorry to bore you with my ignorance ......Obviously this is what my search returned -No Topics Found......or I wouldn't be asking ........Thanks

It's obvious that you didn't try hard enough....

Different bbl twists are for different bullet weights. 1/7" is for heavy to medium weight bullets. 1/8 will pretty much shoot anything and 1/9 is probably the best all around bbl. It will shoot from light to all but the real heavy stuff.

Quoted: Quoted: Please do a search.  That subject has been beaten to death numerous times already. Sorry to bore you with my ignorance ......Obviously this is what my search returned -No Topics Found......or I wouldn't be asking ........Thanks

Then learn to use the search function.

Even a non member like me can find five or six threads on this subject.

Quoted: Quoted: Quoted: Please do a search.  That subject has been beaten to death numerous times already. Sorry to bore you with my ignorance ......Obviously this is what my search returned -No Topics Found......or I wouldn't be asking ........Thanks Then learn to use the search function. hreads

you are right ,I found some .....still didn't find the answers I'm lookin for ammo oracle was informative ,I was lookin for more of a chart/table type of thing ....

For example; why is theAR10 twisted at 1:11.25 ? And what ammo is going to work best with that ? and is said ammo going to put me in bankruptcy to shoot ?compared to say regular cheap Ak ammo ?

The AR crowd typically uses more twist then they need.  For top accuracy, you will see the benchrest guys running the slowest possible twist that will keep the bullet they are shooting stabalized, and no more.  

Not exactly sure what you are after here, but...

The ROT does not narrow the choice of ammo down as tight as it seems you believe. As mentioned, if you are a precision shooter and want to eek the most from your rifle, it is best to decide what you will be shooting bullet wise, then get a tube that optimizes that round, but this is anal to an extreme.

Also as mentioned, the military 1:7 twist overspins ammo, but it is overspun for a reason... you can rest easy that both 1:7 and 1:9 twist in the AR15 platform will shoot a broad spectrum of available ammo.... the current wisdom looks at the 1:8 ROT as the real do-all choice, I would recommend it fwiw

btw: AR10 and *regular cheap AK ammo* are not compatable... AR10 is normally 7.62X51 whereas the AK ammo you are talking about is 7.62X39 -- also, 7.62X39 is not really a .308 bore.

"Not exactly sure what you are after here, but..."


That makes 2 of us ...I've always been a load and shoot guy ...just looking for alittle more insight and knowledge..Dohh! on the AK ammo ...

There are many, many AR shooters that never shoot anything heavier then 63gr bullets, but after they keep reading over and over about you guys spouting off about the tight twists, they go that route when it is clearly not the best choice with the ammo they are going to use.  1:12 will do a 63 just fine.   The tight twists also increase pressure, increase barrel fouling, and slow the bullet.......why do that, if its not needed in your particular application.

If you are NOT going to shoot the super heavy (and slow) projos, going to a faster twist is not in your best interest.

I like the 1 in 9.  I have a lot of ammo options with it.

Quoted:The tight twists also increase pressure, increase barrel fouling, and slow the bullet.......

AGNTSA............

I hope you have instrumented evidence supporting your claims.

Just THINK about tightning the twist up even more...say a 1:2 or 1:3 twist.............maybe you can help us figure this out.

We could tighten the twist up even more, say 6:1.  Every one inch forward, the bullet must rotate 6 times.  Ya think that would disrupt the bullet a bit?  Would it end up coming out at the same speed, faster, slower?  More or less fouling?  Higher or lower pressure?  

It doesn't just go from one perfect condition at 1:7 twist, to completely FU'd at 1: 6.9 either.  Tightening the twist progressively stresses the bullet (probably not linear progression) as any reasonable individual can imagine.  Please, put some reasonable thought into it.

The testing has already been done......50 years ago.  You might want to read some P.O. Ackley writings.  

Quoted: Just THINK about tightning the twist up even more...say a 1:2 or 1:3 twist.............maybe you can help us figure this out. We could tighten the twist up even more, say 6:1.  Every one inch forward, the bullet must rotate 6 times.  Ya think that would disrupt the bullet a bit?  Would it end up coming out at the same speed, faster, slower?  More or less fouling?  Higher or lower pressure?   It doesn't just go from one perfect condition at 1:7 twist, to completely FU'd at 1: 6.9 either.  Tightening the twist progressively stresses the bullet (probably not linear progression) as any reasonable individual can imagine.  Please, put some reasonable thought into it. The testing has already been done......50 years ago.  You might want to read some P.O. Ackley writings.

I'm not talking about the ridiculous examples you have provided.  I'm talking about differences in common twists like from 1-9 to 1-7.

Funny how every time I ask for some sort of empirical evidence, I get none, or get some redirection.

1 : 7

Git R Dun

Quoted: Quoted: Just THINK about tightning the twist up even more...say a 1:2 or 1:3 twist.............maybe you can help us figure this out. We could tighten the twist up even more, say 6:1.  Every one inch forward, the bullet must rotate 6 times.  Ya think that would disrupt the bullet a bit?  Would it end up coming out at the same speed, faster, slower?  More or less fouling?  Higher or lower pressure?   It doesn't just go from one perfect condition at 1:7 twist, to completely FU'd at 1: 6.9 either.  Tightening the twist progressively stresses the bullet (probably not linear progression) as any reasonable individual can imagine.  Please, put some reasonable thought into it. The testing has already been done......50 years ago.  You might want to read some P.O. Ackley writings.   I'm not talking about the ridiculous examples you have provided.  I'm talking about differences in common twists like from 1-9 to 1-7. Funny how every time I ask for some sort of empirical evidence, I get none, or get some redirection.

What is funny is that you seem to jump into a thread and dance around with this

"I hope you can prove that boy" and little laughing characters and other annoying bullshit

...then, when you are presented with the proof you called for, you seem to disapear or dismiss it as not actually, precisely, 100% what you were looking for... stop it, please... there are people on here that are trying to get correct information out and exorcise that (as you put it) arf.com dogma.

The information you have asked for has been presented, it is no secret, it is in POA books as mentioned, check the ARBL maybe? Redstone documents, the trials for the 1:7 barreled rifles, a discussion about why to even go with an overspun round when it does promote some undesired effects... Or just stick some different numbers in your ballistic development software and see what the changes are?

Now, if you have *empirical evidence* of the contrary then please present it... it seems that your recognition of the above post, that the conditons do in fact exist -- perhaps they have to be taken to such extremes as a matter of presentation... I was asked in a previous thread to please provide from data a measurable difference of throat errosion between the two and honestly the percentage of increase is in the single digits, not really a big deal and MV differences may not really go beyond extreme spread... but still facts.

...have you seen the elephant?

will Wolf shoot ok out of a 1/7, despite it being a 55 grain shell( or maybe it's 59)?

Quoted: will Wolf shoot ok out of a 1/7, despite it being a 55 grain shell( or maybe it's 59)?

Will work fine, but its a bit on the fast side for 55gr. It wont get as good accuracy as say a 1 in 9 would for a 55 gr.  

1 in 7 is the twist rate on an M16A2. Definitely fast for the 62gr ammo the US military normally uses, and even more so for the 55gr M193. But the fast twist is needed for the heaver tracer rounds (or at least thats what Ive been told here). Ive been told that this faster twist also causes fragmentation faster, at shorter ranges.

Your best twist rate on an AR is 1 in 9. You can go down to under 40, or up to around 70 with decent accuracy. But probably will work best around high 40s to mid 60s grain.

1 in 8 will do almost as good all around, but is better suited for higher grain bullets. Ive shot 55gr groups under 1" at 100 yds with Federal AE. Shoots best with 69gr Federal Gold Metal.  Generally high 50s to low 70s work good in this twist.

Dont go nuts with all this twist rate and bullet weight crap. Unless you are shooting in 600yd matches or doing long range varmint shooting it wont mean squat. You can read all about fragmenting too, if thats important to you then get some hot M193 or some fragmenting ammo. That stuff will break up fine in anything from 1:7 to 1:9.

My fav rifle to go out and plink with is a  1/12 perfect for 55 fmj m193 ammo.

tag

Quoted: What exectly do the different barrel twist rates do for performance?

The rate of twist determines the optimum bullet weight/length for a given caliber and speed of the bullet by applying the proper spin on the bullet to prevent the bullet form yawing and pitching... Expressed in terms of the number of revolutions per inch of barrel length, this ratio is commonly expressed by designations such as 1:9, 1/9 or 1 in 9 twist, the 1 represents 1 twist, the 9 represents inches of barrel length... A good rule of thumb is that the heavier, or "longer" a bullet is, the faster the twist rate needs to be to stabilize it in flight, therefore a lighter "shorter" bullet needs a slower twist rate to give proper bullet spin for correct flight... Over stabilization of bullets can occur when larger heavier bullets in a given caliber are fired at very high velocities...

In general for the .224:
1x7 Good twist for the 50-100 grain bullets. Excellent accuracy with 60 grain bullets and up...
1x8 Good twist for the 50-80 grain bullets. Excellent accuracy with 55 grain bullets and up...
1x9 Good all around twist ratio. Will shoot well with bullets anywhere from 40-75 grains in weight...
1x10 Good twist for the 40-62 grain bullets, but favoring the lighter side a little more...
1x12 Good twist for the 40-55 grain bullets...
1x14 Good twist for the 40-45 grain bullets...

You can use the Greenhill formula to determine the proper bullet to twist ratio... It is based on the rule that the twist required in calibers equals 150 divided by the length of the bullet in calibers...

This can be simplified to:
Twist = 150 X D2/L (D2 = D squared)
Where:
D = bullet diameter in inches
L= bullet length in inches
150 = a constant

This formula had limitations, but worked well up to and in the vicinity of about 1,800 f.p.s. For higher velocities most ballistic experts suggest substituting 180 for 150 in the formula...

Who makes barrels in 1/8? I know Rock River does, but I believe only in Stainless Steel. I've been looking at a Bushie 14.5" in either 1/9 or 1/7 (special order though). If I could get a chrome lined 14.5" in 1/8, that would seem like maybe the perfect compromise.....though again I'm sure for most purposes both 1/9 & 1/7 work just fine.

Quoted: 8< ---- lots cut out ------ 8<

Outstanding post! And thanks for including that the constant for Greenhill is generally thought of as 180, with the higher velocity rounds used today...