1:'9 1:9.5 or 1:10 twist for 7mm-08?

I'm getting back into this project, and need a barrel for my AR-308. It seems like splitting hairs with these twists though. I would like to use 140 grain bullets, and will reload.

First rifles Remington chambered in it were for 140gr bullets and had a 1:9.25 twist, have one in the safe. What barrel length are you planning on running?

If buying a barrel for one today I would go 1:9 or what ever the Berger twist rate calculator shows would run 162gr bullets. Just making sure to have other options in bullet weight.

1:9 7mm-08 will run 140's up to 168's.

9 twist will do it all. Depending on speed and bullet choice one could get by with a 10 but it's not ideal imo.

I'm 9.5 on ours and they handle everything we shoot

Since an AR already loses 100 fps compared to a bolt gun, I'd go faster twist than what you need. Most 140 grain will work fine in a 1:10" twist. But it wouldn't work well for the 162-168 grain bullets as good. It would handicap the rifle some. I would lean heavily to a 1:9" twist. Plus the faster twist helps with better terminal performance.

I went 1:11" twist on my 300 WM since it was "just enough". I now wish I had gone with a 1:10" to fully stabilize the heavy 30 cal bullets.

Chad,

why do you say a 1:9” will have better terminal performance than 1:10”?

I think Chad is referring to RPS on the bullet, the faster it is spinning the more centrifugal force is exerted making it open a little faster giving a larger frontal diameter a little quicker and separating out those secondary projectiles John Nosler loved for secondary wound cavities. With barnes bullets it helps initiate expansion a little quicker.

Just to make math easy, say a deer is 18” thick.

1:9” will make two cimplete revs passing through. 1:10” will make 1.8 revs.

Does not seem like a difference of significance assuming all other variables are the same.

I went through a discussion here recently on the my recent 7mm08 project with a 1:10 twist.

Results: 17" barrel is shooting 140s and 120s very well.
140 averages 2800 FPS
120 is 2900 FPS

I am digging this little bolt action, too it out yesterday evening and center punched a doe through the top of the head from a tower blind with the 139 GMX.

BTW, I have quite a bit of factory ammo available I will sell off if you want to test some.

Hey Jeff, basically, what kmon explained. When a bullet is spun faster (faster twist), the bullet has more rotational force. When the bullet enters soft tissue and the bullet is upset (expands), it will have more expansion and more of a chance of tumbling and causing more damage. It's the same principal why the military went to a 1:7" twist in the M4's, from the previously slower rifle twists of 1:9" and 1:12" twists. Since NATO regulates the type of bullets the military can use (FMJ, etc), the bullets are difficult to expand. So when you spin them faster with more rotational force, an FMJ bullet will tumble in soft tissue and cause massive damage. It kind of does the same thing with hunting bullets, and allows for the bullet to expand and possibly fragment more.

For example, I had a customer shoot a large buck in the neck last weekend with a 1:8" twist 28 Nosler and 195 grain EOL bullet from about 140 yards. The bullet went in, and never came out. The rotational force on this bullet at that close of range caused massive fragmentation.

Chad,

the difference is 2 revs (or less) vs. 1.8 (or less) revs passing through the deer.

Hard to see how that 0.2 extra rev could be a difference of significance.

Jeff,

You're leaving out the revolutions the bulley made on the way there.

Not following you? Please explain.

The bullet makes one rev in 9" of linear travel or 10" of linear travel.

If a deer is 18" thick (most are less, just picking that to keep math simple), with 1:9" twist, the bullet makes one complete rev over 9" of distance. If the deer is 18" thick, the bullet will make two complete revolutions passing through. With 1:10", the bullet will make 1.8 revolutions passing through.

Jeff, it's not the number of revs, it's the bullet expansion that results from the faster revs. Don't think about 1.8 vs. 2 revs, think about the bullet expanding more and causing more damage. P_102

Guess I am not understanding how a difference of significance of 1.8 revolutions vs. 2 revolutions going though the deer's body can make any difference of significance.

The bullet does not stop and turn high rpm's like a chainsaw.

You guys are not understanding basic physics.
"The bullet does not stop and turn high rpm's like a chainsaw."

The revolutions in a barrel do not correlate to a direct 1 in 9" twist inside a cavity. You need to be thinking in RPMS like a drill. Remember that once that bullet contacts resistance (flesh), the RPM's will decrease. That bullet will still spin a heck of a lot more than two revolutions within the cavity.

See this article:

http://www.accurateshooter.com/technical-articles/calculating-bullet-rpm-spin-rates-stability/

Read it and the article says 1:12" is one rev per 12" of travel.

Twist rate is a measurement of revs per unit of distance traveled.

RPM's is a measurement of revs per unit of time.

1:10" twist is 1 rev per 10" of linear distance by definition.

Whether it takes 1 millisecond or one month for one rev is a function of velocity, not distance traveled.

Perhaps you can quote the sentence that says the bullet slows down and increases rpm's per inch of travel because I am not seeing it in that article.

once the bullet hits, all bets are off

Tend to agree with that. Bullet construction, design, and what it hits matter way more for performance than the twist rate. Just my observation from the animals I've shot using 1:9", 1:10", 1:11.25" and 1:12" twists.

Jeff, it's simply centrifugal force. A bullet spinning faster has more internal force around its axis trying to break it apart, causing it to expand more (or even separate) when it hits the deer. A few days ago there was a post about a bullet spinning too fast and losing its jacket before reaching the target, this is a good example. P_102

RPM's of a bullet is muzzle velocity times 720, divided by rate of twist. RPM= MV x 720 / rate of twist

If you take a typical 7-08 with 140 grain at 2800 fps, here's the numbers.

A 1:9" twist has 224,000 RPM's. A 1:10" twist has 201,600 RPM's. That's an 11% increase in RPM's, which will be even higher % in rotational force. (I don't remember the formulas for that). This rotational force will help in expansion and terminal performance.

But given the pieces of a millisecond we're talking about in the few inches a bullet travels in a deer, I think you are overvaluing the 11% difference.

And If I blew up a 195grn bullet on a deer's neck with no exit, I'd never hunt with that bullet again.

I knew this dialogue would go down this path when I asked the question initially, and knew there would be resistance, but thought it worth beginning to shed some light on a very common misunderstanding. Believe me, I understand how easy it is conceptually to confuse and conflate the two completely different measurements. I did not wake up to the difference until just this year.

I also used to think that the bullet hit a deer doing 200,000 RPM is like a chainsaw turning 200,000 rpm's hitting the deer, and a faster twist rate meant the bullet is spinning 10's of 1,000's of times inside the deer - it is not.

The twist rate literally describes the distance the bullet travels in one revolution. 1 in 12" means the bullet turns one time in a 12" distance - changes in velocity will change rpm's, but do not change that distance traveled per rev. Changes in velocity will change how long it takes the bullet to travel that distance, but it still will be making 1 rev per 12" of distance traveled, or 1 rev in 9" or 10" whatever the twist rate may be.

Once the bullet leaves the barrel it maintains that same rate of rev vs. distance independent of velocity. RPM's do not measure the distance traveled per rev. A 1:12" twist means the bullet will make 5,280 revolutions traveling 1 mile, which is 5,280 feet. Higher velocity will increase rpm's, but it will not change the number of revs made in the 1 mile distance. A bullet fired from a 1:10" will make 6336 revs in 1 mile regardless of velocity will effects rpm's.

Changes in velocity can change the time it takes to cover that distance and will change the number of revs in a minute, but will not change the number of revolutions over that distance.

Jeff,

You are still failing to grasp the physics and the math. The twist rate causes the spin. After that, RPM become a function of velocity. Velocity over distance traveled is not a constant. The RPM slow as the velocity slow, as does the distance traveled. Simply way to look at is, are the initial twist rate, velocity, and atmospheric pressure conducive to stabilizing a given bullet over a given distance? Think of throwing a football. And some point the decreasing rotation/gravity/atmospheric pressure cause the football to become unstable and wobble. Same thing happens to a bullet. The football does not maintain a constant velocity or spin, neither does the bullet. Ie. the closer the receiver is to were the football is thrown, the more spin the football will have, the more stable it will be, and the faster it will be traveling.

Other factors are involved, such as shape (b.c.) and length of projectile, but it is still just basic physics. Think of throwing a ping-pong ball and a javelin. Both may leave at the same rate of speed, but distance traveled and maintained speed or rpm will vary. So many variables, grins. That is why there are twist calculators. Enter your b.c., velocity, and altitude and it will spit out an appropriate twist rate. Or just shot a Nosler Partition and kill stuff...grins. I would much rather have a "tough" bullet, than worry about impact RPM's and collateral damage.

No, I am grasping it quit capably.

You and most including myself until recently fail to grasp what the twist rate represents.

The twist rate literally measures the distance traveled per revolution of the bullet.

Again, the twist rate is a measurement of the distance it takes the bullet to make one complete revolution.

That measurement is independent of velocity, time, or rpm's which only measures revolutions in a minute.

RPM's measure revolutions per unit of time, independent of distance traveled.

A chainsaw can turn 10,000 rpm's without moving any distance at all.

The issue under discussion is how many revolutions of the bullet occur when the bullet travels through a deer. That can be answered knowing the twist rate of the bullet regardless of its velocity or rpm's. Changes in velocity will increase or decrease rpm's, but not the distance traveled by the bullet per revolution.

For the sake of discussion, please explain if a 308 175 grain bullet is going 3,000 fps fired from a 1:12" how many revolutions of the bullet occur in a distance of 12"?

Jeff,

You are correct on the first. But your issue under discussion, there is no correlation. You fail to factor in resistance and the fact that the 1 in 9" is NOT a constant. I am out.

Jeff, everyone on this thread understands twist rates...we're trying to get you to understand (at your request) why a bullet fired from a barrel with a faster twist can cause more damage. Hell, I don't even hunt deer and I understand it! Out also. P_102.

P,

I “understood” it the same as all of comments until earlier this year, when I really focused on determining the specific question of how many revs actually occur inside the body of the deer. At first I was messing with velocity and rpm’s, then the answer was obvious and simple. It is very easy to conflate rpm’s into the actual number of revs, when they represent very different measurements in this context.

The factors that really matter for terminal performance are bullet design, velocity at impact, and what it hits. Some expand, some tumble, and some fragment, and some bullets do a combination of those performance factors. Impact velocity can make a major difference in terminal performance and bullet performance.

Twist rate influences bullet stability and may decrease or increase the likelihood of yaw and tumbling and fragmentation, so it potentially may matter with some designs and placements, but an extra 0.2 revs inside the cavity is not making a difference of significance.

Here is a slow twist, 1:12" 175 SMK at about 50 yards from earlier this week. This was a cull deer with a broken leg. The distance was about 40 - 50 yards walking almost straight away. He had a deformed antler I wanted to preserve for a euro mount, so a head shot was not an option. Since it was for the freezer, spine shots would have destroyed too much meat at this close distance. He was angled ever so slightly left, so put it down the left chest wall aiming to go behind the shoulder and hopefully not ruin the leg. He went about 15 - 20 yards. Any way, here is a slow twist with the 308 175 SMK's, which I keep reading "pencil through." The point of aim/intial impact is the back end of the rib cage and it plowed mostly straight forward and tumbled as the 175 tends to do.

Only a small portion of the leg meat was lost, the backstraps were untouched.

Because you're still insisting on counting the number of revs inside the animal I have to believe that you still don't get it. Good hunting. P_102

What the bullet is actually doing inside of the body is what matters for terminal performance.

All the faster twists are just to stabilize the longer heavier bullets. Jacket thickness and bullet construction is what determines the terminal effects. How many rpm's is meaningless.

Precisely.

I'm with these two^^^

Think about RPM, or revolutions per minute for a second. Even at 200,000 rpm that is only 3,333 revolutions per second. What is the flight time to a game animal? Assuming a muzzle velocity of 3000 fps (constant w/no decay) it only takes 0.1 second for the bullet to reach its target at 100 yards so that is only 333.3 revolutions. While 200,000+ rpm sounds like a lot there are no bullets that fly for anywhere near a minute therefore they achieve a much lower number. Maybe that makes sense to some maybe not, but I completely do not buy into faster twist rates causing a measurable amount of damage more than slower.

Not really interested in the larger weight bullets, so this sounds good so far. I know I'm losing some FPS, but I've been wanting an AR308 for years.

Plan on 20-22". Not really going to be hauling this things around too much, so I would like the speed gain from a longer barrel.

(2) revolutions,inside a Deer?!?

Oh I'm CRYING...I'm laughing so hard!!!.............

My 22" Lilja 1-10" SALAMI 7-08,will stabilize 162A-Max at low tide,when freezing,if only as a matter of fact...mainly because it is a fact.

Throat,Twist and COAL determines what you can and can not shoot,as stability and housing same goes. A chambering can simply be no better than it's bullet and bullets matter wayyyyyyyyyyy more than head stamps. Now the only way bullets get better(BC increase),is to get longer,which requires more RPM and more COAL latitude.

I'd not build a 7-08 slower than 9",if only because I've got 'em in all twist rates cited. I also wouldn't build a 7-08 on a '10 Krunchenticker,due COAL latitude. I'd go Kreedmire all the way,because it'll shoot softer,jump to lands less and will outperform same. Doubly so,when talking an idea as poor as slummin' .284" 140's in a Self Shucker.

Hint...............

Ok Larry, if a barrel has 1:9” twist how many revolutions will the bullet make in 18” of distance traveled?

Do agree 1:9” is the way to go for 7mm as been through five of them. They handle 140’s - 180’s and all in between.

You are fixated on Fluff,which has no bearing,as to how gross RPM is both measured and interacts upon Victims.

I realize that you are doing your best however and that is the ONLY reason it is funny.

Hint..............

No, the initial issue was argued by others that 1:9” is deadlier than 1:10” all else remaining the same. My point is that 1” faster twist is of no significance in terminal effect.

Since you were laughing and crying at the fact the bullet only makes 2 revs in 18”, please regale us with the calcs from the Coos Bay High math department.

Sweetheart...the barrel don't pass through a Critter and upon impact,the lineal velocity is MUCH different from it's gross RPM,so they do not track in sync.

Hint.

Who chews your food for you?..............

You can’t calc an answer?

I assume your Mom?

Bless your heart............

The bullet will conform to the rate of twist as long as it's in the barrel. As soon as it's in flight, it begins to shed velocity. Rotational velocity will decay also, but not nearly as fast as the bullet's forward displacement velocity decays. It won't work out to revolutions per distance traveled because of the velocity loss. It would work out to revolutions per time of flight, minus the rotational velocity loss...and ultimately is a waste of effort in the end.

Just one question.....do you spit or swallow....everyone can clearly see what you are......on you knees as much as kaepernick....

Just curious since you are clearly the smartest man in you own mind.....like to hear how the "expert" does it....I'm guessing you swallow....

Surely they taught math at Coos Bay High, right?

Still no answer?

Well looky there...someone shoots a bit.(grin)

By GOD,there's hope!..............

Weren't my intent to horn you up and there really wasn't a need to make a show outta coming out of the closet...it weren't no "secret". Hint.

No slighting your taste in men though. Pun be intended.

Hint.............

Gonna get quiet again and yet another one,is gonna hit reverse.

What were the "odds"?!?

Hint..............

You clearly have a lot of valuable knowledge that could greatly benefit lots of people....but you are more interested in showing how big of a prick you can be than actually add any real value to the discussion....

Swallow away buddy.....

PLEASE find me "mistaken",I assure you it will be FUNNY...though for reasons beyond your "comprehension".

Hint.............

Never said you were "mistaken".....said you are a prick that doesn't add any value to the discussion....move along troll....

EDIT: Sad part is that your "knowledge" could be helpful to lots of people, but that's not why you are here for is it.....

PS and by the way,of course I am NOT "mistaken". I'm simply afforded the luxury,of not being forced to guess and that Fact very much troubles Window Lickers.

Hint.............

I'm guessing you were either ignored or abused as a child.....I blame you parents either way....

No need to fuel your Homoerotic Fantasies...just slip back in the closet.

Bless your heart..............

RR,

trying to keep it simple for Larry. The decay in rotational rate is going to result in a lower number, not higher.

So reckon we’ll never see any attempt at a real answer from him for the simple reason he is “mistaken.”

Got to head out, but will check in later.

ps for Larry on the other thread, 208’s are ok, 210’s are better, but .896 at 2950 bests both. google it.

Pass the 1.05 BC and hold the Fluff. The only thing you "shoot"is your Imagination and Pretend.



Now you can say you've "seen" one.



Hint..............

No. Since velocity is decaying much faster than the bullet's rate of spin, the rotations per unit of distance traveled will actually increase as long as the bullet is in flight. If you've retained 97% of your rotational velocity but only 80% of your forward velocity, it cannot be any other way.

Let her try...because she is doing "GREAT"................(grin)

You referring to jefdbird as her?

He is one of the nicest MEN on this forum, as well as a very experienced shooter and hunter. As well as a husband and father. Referring to him as "her" is a slap in the face, and you have done it to everyone in your few hours around here.

It won't be long now, and you will be gone forever.

Man Crush!

Bless your heart.

Hint................

I'm limited to the magazine capacity of the AR-308. Hopefully that helps. I don't want to use too big of a bullet so I don't have to give a up a lot of powder capacity in the case.

Factory ammo of all weights,will happily nestle '10 Krunchenticker mag confines.

You are fretting that,which don't exist.

Hint...........

you have me confused.

Changing COAL 1/10th of an inch(.100"),will not offer a "Magical" velocity advantage. What it will do,is keep the ogive closer to the throat,which typically increases raw Accuracy potential.

Long story short,you can scoot a 162 to 2600fps easily,in a 20" Krunchenticker 7-08,that is feeding from it's OEM mag confines. I'm an ASC Slut,because they are tough,reliable and the most generous in COAL latitude(2.825" COAL easily). 140's cannot begin to hang,a that COAL or any other.

Hint................

Got it now. I found those mags earlier, but never have heard of them. I have some Pmags right now, but think the plastic is a little thick. I think I'll try a few of the heavier bullets when I start testing. LaRue makes a good metal magazine, but I don't think it's worth $80.

ASC,ASC,ASC...roughly in that order.

They STEAL the show.




7-08 AI/162A-Max shown.

Hint..............

Now that Mr. Hint....hint is gone whose right?

Ran past someone who studies bullet performance among other things for the .mil.

Here is his answer: "Usually forward velocity slows before rotational. However, some bullets nearly stop spinning altogether when impacting."

So would that mean Chad is correct?

The who is correct is not as important as what is correct, but looks like expert's answer is different than all others thus far.

RR had the correct answer for the bullet in flight, but no one had the answer for what happens at impact, which appears to defy all of the theoretical jabbering. Doubtless our tax dollars are at work trying to find some way to predict what happens and how to improve the terminal effects as it seems inconsistent and unpredictable. Have to say that was a surprise.

Here is another example whwre I need to trap hogs, execute, and prop them up on a berm, and perform some "ballistics testing". Followed by autopsy.

EXCELLENT notion.

That would be a lot of fun but I don't know that you can get an adequate sample size to say anything definitive.

Hold my beer.

!

That's what I like to hear.

Jeff, did the expert say which bullets stop rotation and which ones continue to rotate after impact? Is there a type of bullet that is more apt to stop than another or is is just dependent on what it hits or more of a mystery? Just curious, don't know if the conversation went that far


Some recovered mushroomed bullets show a definite rotation force at work on the bullet that sometimes matches the rifling on the shank and others IIRC show a bit more at the tips, Barnes copper bullets the tips of the petals are often curved more than the rifling marks indicating to my thinking those bullets were still rotating. Then of course there is more forces from that rotation the further from center the petals get. Just principal of dynamics old style sling shot as an example the rock sent out is moving a lot faster than the string at the location It meets the hand. Better example perhaps an ice skater arms in spins fast as the arms go out the spin speed slows.

Following the skater example the faster the bullet expands outward the faster the spin force would slow down. It is not uncommon to find bullets like the Swift Sirocco that holds together for most times 90 percent weight retention and large diameter for caliber ending form to ne rear of the bullet going forward in jell and when it stays in the body of game heal of bullet furthest from the entry point. I have read about that several times and seen it in critters at some point the bullet lost stability and turned going through gel or soft tissue and a parachute type effect turned the bullet with the heel of the bullet being the pointed end at the time of instability and the parachute effect of the expanded front end catching and slowing it down from a tumble.

Looking at some high speed video of bullets the ones with no penetration that fragment on steel look like they are rotating with the rifling marks until they get very short where they look like are loosing rotational forces. the bullets that punch through steel are still rotating.

I think it would be interesting to have the highspeed camera on a gel block and shoot bullets out of one box for consistency into it at the same velocity from different twist rates and see if they flip around at the same depth of penetration.

Of course I could be totally wrong on what is in my head about what happens, but in reality as long as the bullet efficiently kills the critter I am happy.

No, I asked if there is any explanation or pattern, and not that they have figured out yet, but it was just a short note both ways.

What is obvious is that is way beyond my high school and college physics, but that was many years ago.

My young nephews show how they do math and it is completely bizarre to my eye.

Might be useful to start a thread on combinations of bullets with shot placements that are known to work well, and ones to avoid.

That could be a useful thread.

Never took high school physics but in college took physics, statics, and dynamics but that has been years ago. Agree on the math of today it sure is different but still comes out to the right answer if done our old way or the new way if done right. I should have taken one more advanced math class when I was in college and would have had a minor in math, that wore out lots of pencils, paper and hours as it was. Adding a bunch of numbers at work one night and a younger lady doing the same, she got out a calculator I just did a list about twice as long in my head and was finished ready to go before she got half way through her list. She just once again said I am not human and not from this planet. Heck according to her I might be from that little planet that lost its ranking.

Put any bullet you want through the braim stem. It'll work.

No, brutha...that would mean that yours truly is correct.

You know you can chootem more than once. Just an idea.

I hope I'm linking this video properly.

I could be misinterpreting what I see and jumping to the wrong conclusion, but this clip sure does suggest that the bullet does retain some spin as it penetrates. It may not be all that simple though, meaning "it depends."

Gave you the prize up above.


I think he means what happens after impact is inconsistent and unpredictable.

What, you went and made me another year older?? Well thanks a lot.



Just kiddin Jeff.

Hit the wrong smilie the first time. Fixed it.

You shoulda just left it...it was funny!

That's exactly what I meant.

Hogs are such good bullet test media

We can round you up a 175-200lb pig or 3 when you want to test this hypothesis. Just depends on how the night before goes

Okay then...I guess what I was really wondering about is why you hafta trap em first.

Traps are on duty 24 hours a day, so that increases likelihood of obtaining ballistic media.

I have not seen my local sounder in months. They will be back, I have no doubt.

Pigs are very smart. They probably figured out your range was a rough neighborhood.

One day in May, one of those prefect weather days, 72°F, 5 mph south breeze, not a cloud in the sky. I was working in the shop, and I heard them. I worked my way toward the sounds. They had the audacity to cross my range, at noon, on a clear day. Toting an LR308 I decided to creep the 400 yards seperating us, so I could get more shots off. They crossed onto my neighbors place, and by the time I got to their crossing they had vanished.

There was a reckoning the next day, though. I was teaching, and in our last hour, we heard them down at the end of the range. My customer left and I went to repaint the targets on the four wheeler. Same LR308, and this time I discovered them 200 yards away. I walked an additional 50, rested the rifle on the second barb wire from the top, and prayed for reliable cycling. The survivors have not been back. So yeah, they may view it as a rough neighborhood.

I have herd you have had problems with ARs in the past and was a little surprised when you got one
Had a sounder hitting one feeder t a lease that didn't learn the first time, one of the other lease embers shot one out of it one weekend. I got the rest the next weekend. 9 at the start 0 at the end. Got those 8 with a bolt action 22-243 mostly with 75gr Siroccos not loaded that hot at 3300 fps. Started with the one that was the furtherest out and kept shooting that way until the last ones from the stand were 10 yerds. reloaded agsin and got the last 2 as they ran from the brush at about 30 yards. Gotta love the young pigs that never get a chance to learn. Biggest one of those was about 100 lbs

AR problems and JG in the same sentence He has a gift as the church people call it

One of the Police Sniper teams that train out there, had some GAP-10's out one day. One of those malfunctioned, in my presence. I didn't even touch it, and it failed to eject a few times.

You were NEAR it, though, right?

Precisely.

So, in short, I'm supposed to get a 1:9?

Oh that, the original question? Yes.

This thread hit so many tangents glad to see it is

Agree 1:9 is a very good twist for a 7mm-08.

11/09/2017 11:52 AM

11/09/17 11:11 AM