Talking to my cousin today and he asked what twist my new PSA had. I said 1:7

He's like ah man you need a 1:9, Bob said........



I told him that a 1:7 was better for heavier bullets and does well with light bullets also.

He was like

I tried to explain to him that in 7" it will go around once compared to 9" and will stabilize the bullet.

Other than reading extensively on ARFCOM , I cant really find a link to bbl twist rate and comparisons with different weight bullets.

Any help?

Thanks

prepare for a heated thread... should be fun to watch

Ready for the heat

If I can understand it then anybody can.

It's based on the bullet length. Shorter bullet like a 22LR will use a 16" twist a 90gr. will use about a 7" given similar calibers.
http://kwk.us/twist.html

if you shoot good quality ammo the 1:7 is just fine for pretty much everything. If it's cheap out of balance super lightweight then you will have problems magnified with the faster twist.

You are correct.  Your cousin is wrong.
1/9 are good up to about 69 grain ammo.  Higher grains than that from a 1/9 will loose stability.  
They way you know you are losing stability is either key holing or bad accuracy results.

This is not correct somewhat misleading.

Lightweight, thin jacketed varmint bullets (think 40 grain) run the risk of coming apart due to the high rotational forces. This is exacerbated by the higher muzzle velocities of these lighter rounds. Do yourself a favor and do the math using twist rate and muzzle velocity. I think you'll find the bullet doing about 400,000 rpm.

Bear in mind that a 1:9 might stabilize heavier bullets at given temperatures and pressures.  Changes in temperature, air density, and other things could conceivably destabilize a bullet in Alaska that worked just fine in Arizona.

Maybe not to the point of keyholing but accuracy will suffer.  1:7 is just more versatile because most available ammunition on the market is made in the 55-70+ range.  And all of those shoot just fine in 1:7.

I've never seen the result of a bullet flying apart.  But I'd like too.

Has anyone?

I sure haven't (at least out of an AR), and to settle an argument once just like the OP's I handloaded a batch of 40gr Nosler Ballistic Tips to max pressure and fired them out of a 20" 1:7 Colt HBAR.

My buddy practically dove for cover as I squeezed off my first round-he was apparently expecting grenade shrapnel to come out of the barrel

It was a lot of fun to gore that particular sacred cow on his behalf. Once he saw the nice round holes in the quarters I was shooting he finally shut up about it...

If you bought a 1-7" twist barrel, that's well and fine, but I think there is nearly ZERO need for it.  Unless you bought your AR just to emulate GI Joe, the "other" use for it would be as a varmint rifle.  The absolute heaviest varmint bullet available to handloaders in .223/5.56 is 60 gr.  Otherwise, you're most likely to use the cheapest ammo you can find, for range blasting.  This typically comes in the 55 gr. flavor, with Russian Steel cased stuff available up to 62 gr.
I have a 1-9" twist barrel, ON  PURPOSE.  I have seen bullets disintegrate in flight, when I was a range safety officer at the Lee Kay Center, in Utah.  The guy was shooting a .257 Weatherby, with factory ammo.  At first, we couldn't figure out why there was no impact at all on the 100 yard berm.  After a few shots, I noticed that each time he fired, there was a fresh black line in the snow, extending about 30 feet in front of us.  There was no-one else around, so we moved over a coupla' lanes, where the snow was virgin in front of the bench.  Sure enough, it kept happening.  I don't know if he had had the rifle rebarreled, or what.
My point is that if you intend to use your AR with varmint bullets, the slower twist makes far better sense.  The jackets of quality varmint bullets are thin, by design, and there is a limit to how fast you can spin them before they disintegrate in flight.  That difference between 1 turn in 7" and 1 turn in 9" seems small, but a little bit of math is very revealing.  Figure the same bullet, covering just 6 feet (72 inches), regardless of velocity.  The 1 in 9" twist spins 8 revolutions, and the 1 in 7" spins just over 10.  That's 20% faster.  If you wanted to use something like the Speer 52 gr. HP, you could expect to reach about 3,200 FPS from a 16" barrel.  With a 1-9" twist, I think you'd be fine, but with 1-7", I think you'd have to keep a close watch over the disintegration problem, and maybe drop velocity a bit to control it.

That's too hard to read.

I think this myth may be born in WWII when center fire cases where swaged from 22LR shells in a .220 Swift

It is not a myth.  It is very real.  Most will never see it.  And it is not common..

 

Ah, okay........

im gonna load up some 90 grn tracers and go play in the arctic with my 1:7 if i want to put some 35 grn bbs in some cans i got a cheap 1"9 upper and id probly still try them through the 1:7 just to see

Fella' has a video above, might want to take a look.  Since it's a myth.

1-there is no need for you to scrutinize his choice in barrel, either by price or by luck he has a 1:7"
2-the absolute heaviest hand load is NOT 60gr., personally I load 68gr, and occasionally find 70 & 72 gr when I'm lucky.
3-have you really seen bullets disintegrate in mid flight?     I THINK NOT  if so you're in the wrong industry and should be studied like a lab rat.

Invalid, your argument is... Invalid.

Damn, you didn't watch the video either.  Pretty good proof right there.

and as far as the video goes, who uses 35gr rounds anyway?  they were hand loads?  for what? those did not look like .223/5.56 rounds.  i suspect something fishy

Yeah, typical response.  Since there is proof then when all else fails just claim that nobody uses those bullets anyway.  I mean, after all, nobody needs those right.  There is nothing "fishy" about that video.  Hell the whole purpose was to prove that you could shoot light bullets accurately.  Look who posted the video on youtube.  That's Superior barrels.  Why would they show you one of their barrels destroying bullets?  What do they have to gain?

Admit that your wrong and move on.  It can and does happen.  Never will happen to you or me, but it does for some.

I'm sorry for singling you out Invalid, but a couple of observations need to be made:

1) Someone who defends 1:9 always uses the line "just to emulate GI Joe" when discounting the utility of a 1:7 barrel. It's as dependable as death and taxes. Why is that exactly?
2) The heaviest bullet available to handloaders that is readily available on retail shelves is the Hornady 80gr A-Max. The OP didn't mention varmint rounds at all in his post.
3) Many of us who have ARs tasked for defensive use prefer heavier OTM rounds like 75gr Hornady TAP or Black Hills 77gr Sierra in our defensive weapons. A 1:9 barrel may or may not stabilize those heavier rounds. Of the eight 1:9 barreled ARs I currently own, six of them handle the heavy stuff fine and two do not. That's a 25% failure rate-just in my personal collection.
4) Most surplus or cheap plinking ammo is 55 to 62gr, and 1:7 handles that just fine. Test after test by members here has demonstrated that there is no appreciable difference in accuracy between 1:7 or 1:9.

My two safes are chock full of 1:7, 1:8, 1:9, and 1:12 ARs, a couple of 1:7 Sigs, and a few other oddball rifles. There isn't a round I can handload that won't work in my 1:7 ARs and Sigs, but there are rounds that won't work in my 1:9s and 1:12s. With that in mind, 1:7 (or perhaps 1:8) is the most versatile for me.

When I buy reloading components I do so twice a year, and in a group with several other people. We decide what we want and combine our resources for quantity pricing. One year we decided to buy 40gr Noslers because my buddies out west were big into prairie dogging-I ended up with 11,000 of the damn things There is no way in hell I would have taken part if I didn't know up front that they would work. I'm about 8,500 rounds into that 11k, and the only problems I've ever had were due to a light crimp-the 40gr Noslers don't have a cannelure. I load those 40gr bullets on top of IMR 4198, and I load them HOT.

Never had a problem with fragmentation/detonation/keyholing in any of my rifles

Oh, and per the video above, a lightweight V-Max...really? That's what you're going to use to "prove" your point. Come on man

In closing, even if I didn't reload-the likelihood of me needing to shoot a heavier bullet is far greater than my need to shoot a varmint bullet. For that reason, 1:7 or 1:8 is the most versatile in my book.

I want to single you out just for a moment
You need to re-read what invalid said.  I see whatever he said has irritated you.

1.  He did NOT say that 60gr was the heaviest bullet available to handloaders.  He said that 60gr bullets were the heaviest VARMINT load available.  He mentioned varmint bullets because they have thin jackets.  That is what they are designed to do.  Basically explode after impact.  That's why the problem is only seen on lightweight bullets with thin jackets.

2.  I don't have a problem with a 1-7 twist.  I have a problem with the "myth" that everybody is better off with one.  I would imagine invalid feels the same way.

3.  Ok, so you like having the option for heavier bullets in a self-defense situation.  I gotcha.  I'm with ya.  What kind of range do you think this self-defense situation would occur at?  Down the driveway?  Across the living room?  From the porch?  Do you really think you will need optimum stability at those ranges?  I'm not trying to be a smart-ass.  Just trying to be logical.

4.  Invalid did not post the video.

I personally believe that the "standard" twist rate for civilian AR's should be 1-8.  I think it serves the light and heavy-weight bullet crowd much better overall.  But that's just me.

My buddy loads 90 grains it crunches the powder when you seat them. If they're really super cheap rounds and they fly apart o well don't use them in that gun but the 35 grain rounds i am finding are like $20+ for a box of 20 either lead free or hornaday super performance varmint. I'd be pissed to pay that and have them fly apart and why the heck would you use them.

Thank you, Four Sixty.  And thanks for allowing that I can have my own opinions.  I have

only one AR, and I find that it's very very difficult to carry more than ONE long arm at a time.  

No matter how many you have in your warehouse, you'll find the same is true for you.  Just

ONE at a time.  So I made this one up to be my single AR.  I believe that once you exceed

about 65 gr. of bullet weight, you find that velocity goes so low that you are shooting with

less power than the cartridge is capable of.  This is one reason why they are called "heavy for

caliber".  Further, since we are able to use any bullet we want as civilians, I am pretty danged

sure that the Sierra 65 gr. Game King or the Win. 64 gr. PSP will prove, every last time, to be

much more powerful and effective at any distance you can actually hit with a 2 MOA carbine.  

This, because that's the optimum bullet weight for the caliber.  Our military is not allowed to

use these bullets, or you can be sure they would.
If you look at what is being used in actual matches with the 75~90 gr. bullets, you'll find that

the .223 Ackley Improved is greatly preferred, and in bolt action rifles, at that.  The heaviest

bullet that can be used in a 5.56 AR is the 77 gr. SMK.  Don't tell me how smart you are

because you're going heavier.  The bullet makers warn against it, and that is not the least bit

smart or advisable.
You don't know what I've done, or where, or how, or for how long.

I love this topic, it brings out the fighting words. I read that the reason the military uses the 1:7 twist is due to the length of the 5.56 tracer round. I have also always been told that it is the length of a bullet that determines twist rate. Just because a bullet is lighter, doesn't mean that it will always be shorter. It is a good rule of thumb to go by though. Nobody ever seems to mention length in these debates.

Unless you are shooting considerably longer (heavier) bullets than normal, 1/7 is better. But I've gone as high as 77 grain in a 1/9 twist with good accuracy. My go-to ammo is 193, so it's a toss up for me.

Yes. I tried a 110gr FMJ in a light 30-06 load, probably traveling 3000fps in a 1 in 10 twist. Only fragments, of the bullets hit the target periodically at 200 yards.