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Posted: 3/8/2006 9:44:55 PM EDT
[#1]
click on search and type in the word "twist" ...search in AR15 Forum....
And you will find more than you will 'want' to know. |
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Posted: 3/8/2006 9:48:07 PM EDT
[#2]
Oh, and here's lots of info: www.ammo-oracle.com/body.htm
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Posted: 3/8/2006 9:58:31 PM EDT
[#3]
Short answer : no.
Long answer: The 1:7 is to stabilize the extra long M856 tracer rounds and unless you're shooting extra long bullets like that, its not necessary. |
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Posted: 3/8/2006 10:33:09 PM EDT
[#4]
I prefer 1/7.
I've used a 14.5in 1/7 barrel out to 550m using both 55 and 77gr rounds. I've not had that success with 1/9. If you want to shoot the heavier match ammo (77-80gr SMK, or others) the 1/7 is your best bet. I usually shoot 62gr ammo, which a 1/9 can handle fine, but I like having the ability afforded by the 1/7 to shoot heavier rounds and make longer shots more reliably. YMMV. |
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Posted: 3/8/2006 10:37:07 PM EDT
[#5]
tucansam, Gimme_A_Carbine is right. If you know you won't go below 55 but you might want to go above 70, go with 1:7. |
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Posted: 3/8/2006 11:23:24 PM EDT
[#6]
I beg to differ with Gimme_A_Carbine. We shoot 14.5 chrome lined 1-9 twist barrels out to 700 yds with 55gr mil-spec ammo using dart targets which is like a popper that resets on it's own. Regularly we are shooting at 400yds hitting 8 and 12 inch plates with the same set up.
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Posted: 3/8/2006 11:25:44 PM EDT
[#7]
There is NO REASON AT ALL to get a 1/9 barrel unless you want to shoot 45gr ammo in your AR.
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Posted: 3/9/2006 12:04:13 AM EDT
[#8]
Not true. A 1/9 twist will be inherently more accurate than a 1/7. The faster you spin a bullet, the more centrifugal force will act on the bullets. Any small weight imperfections in the bullet will show up in accuracy. A 1/9 will also have less rotational land drag than a 1/7 and will result in lower internal pressures, which in turn will result in less barrel wear. Required twist for bullet stabilization is NOT a factor of bullet weight, but a factor of bullet length vs. the diameter (or caliber). Therefore, a bullet that has a flat base and a slightly round nose can be stabilized by a much slower rotation than a bullet that has the same weight but is a boat tail and pointed nose. Your best choice in barrel selection will be to decide the absolute longest bullet you ever plan to fire and then select the slowest twist that will stabilize it. This can be calculated using the following formula: 150 x diameter squared divided by bullet length = required spin Example: for a .224 caliber bullet .70 inches long: 150 x .224 x .224 divided by .70 = 10.752 inches So, for the example bullet, a spin rate of 1/10.752 or faster is required The formula can also provide the maximum bullet length which can be stabilized by a given barrel twist. The formula becomes: 150 x diameter squared divided by twist rate Example: for a .224 caliber barrel of 1/12 twist: 150 x .224 x .224 divided by 12 = .62 inches The barrel will stabilize a bullet that is .62 inches, or shorter. |
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Posted: 3/9/2006 12:18:36 AM EDT
[#9]
Can you tell an accuracy difference of 1/7 vs. 1/9 with standard FMJ ammo in a chrome lined barrel? How many chrome lined AR barrels have you worn out? My guess is "no" and "none". |
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Posted: 3/9/2006 12:41:58 AM EDT
[#10]
The original question mentioned nothing about chrome lined or FMJ. Those are assumptions. To answer your question, yes I can tell an accuracy difference between 1/7 and 1/9 ... and 1/12 for that matter, however I don't shoot regular FMJ ammo. I have never shot out a chrome lined barrel but I would still consider barrel longivity a "real advantage" as the original question asked. |
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Posted: 3/9/2006 1:05:03 AM EDT
[#11]
This formula does not take velocity into consideration. Heavier bullets tend to have lower velocity and thus lower RPMs and less stabilization. A longer barrel of a fixed twist also imparts more stability than a shorter barrel with the same twist. The bullet shape is also not given any consideration which makes me not give that formula much credit as the be all and end all of twist rate considerations. |
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Posted: 3/9/2006 2:52:06 AM EDT
[#12]
The multiplier of 150 is incorrect for pointed bullets. The Greenhill formula (which that is) was designed for round nose lead bullets.
Cheers, Phil |
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Posted: 3/9/2006 2:58:20 AM EDT
[#13]
Granted, this is a simplified version of the Greenhill formula, and IF someone were going to have an exact twist (i.e. -- 8.2:1) barrel made, they would need to factor in the exact intended load velocity as well. However, to determine a factory twist, the deviation in muzzle velocity between a std. 55 grain and a std. 75 grain is not enough that the short formula will not work. Your statement about a longer barrel imparting more stability that a shorter one is absolutely FALSE. All else equal, the only benefits of a longer barrel are increased muzzle velocity and lower muzzle pressure. By "bullet shape" I have to assume that you are referring to the ballistic coefficient. That has nothing to do with stabilization -- only how fast the projectile will slow down. On the other hand, bullet shape does impact bullet length (which is considered in the formula), thus my statement above about a flat-based, round-nosed bullet. |
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Posted: 3/9/2006 2:59:57 AM EDT
[#14]
Given your parameters above there's no advantage for you. That said IMO the 1/9 twist is old school for the newer 1/7 twist allows the use of the BEST self-defense rounds available for the AR15/M16 platform; the 75grn Hornady match HPBT and the 77grn, Sierra MatcKing. YMMV, but I've upgraded all my M4s to the faster twist. Mike |
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Posted: 3/9/2006 3:11:27 AM EDT
[#15]
Same price, same availability? 1/7.
Slightly higher price and less availability for 1/7, and you do not shoot anything heavier than 75gr (20") or 69gr (16"), go with 1/9. Every time I wanted to build up an AR, I looked at 1/7 twist barrels and they were either $30-$40 more expensive or backordered for weeks (because people wanted to be tacticool and get 14.5" 1/7 twist or 16" 1/7 twist) so i went with 1/9. I shoot 99.999999% 55gr/62gr ammo, the cheap stuff. |
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Posted: 3/9/2006 4:21:34 AM EDT
[#16]
My experience with the 1-7 and the 1-9 is that the 1-9 will group 55gr mil-spec ammo better than the 1-7. I am not saying that the 1-7 can't shoot the 55gr, but a 1-9 will shoot it more accurately. We have tested colt barrels, bushmaster, dpms, JT, Mod 1, CMMG, wilson/rock river, kriegers, lothar walther, olympic, and LMT. I rarely shoot anything other than 55gr ammo and the 1-9 more often than not wins hands down.
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Posted: 3/9/2006 5:50:35 AM EDT
[#17]
hummmm... some good info, some bad
...oh well. Use 180 for K in the old Greenhill Formula when using it with modern higher velocity rounds. For accuracy, the trick is to use the slowest twist possible while still getting a good stability factor on the round -- things vary a bit, but most think that anything over 1.5 is not needed, as stated earlier, the higher stabilization factor can exacerbate any potential accuracy problems the round may have. This is not true however for a battle rifle... but, as Steve once said one here, the arfcom way is to: "Define what you need, then buy what you want" |
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Posted: 3/9/2006 9:49:51 AM EDT
[#18]
Higher RPMs yeild greater stability. Higher velocity means higher RPMs. Also the stability of a bullet depends on its shape and center of gravity. Round nose vs boat tail is just an extreme example. Please explain where anything I said is FALSE. I dont see it, enlighten me. |
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Posted: 3/9/2006 9:57:44 AM EDT
[#19]
BOTH SHOULD BE BANNED FROM CIVILIAN USE!!
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Posted: 3/9/2006 10:29:29 AM EDT
[#20]
Higher RPMs will exacerbate an imbalance in something, hence the reason you balance your wheels. The faster you sping something the more that imbalance will show itself. |
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Posted: 3/9/2006 1:41:11 PM EDT
[#21]
Shouldn't the "Bullet Length" part of the equation actually be the "length of the Bearing surface" portion of the bullet..., instead of the entire bullet length??
Also...., if I remember right the 150 Constant in the Greenhill Formula does not work correctly for bullets that will be traveling over 1800 FPS. |
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Posted: 3/9/2006 1:50:12 PM EDT
[#22]
+1 
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Posted: 3/9/2006 2:09:48 PM EDT
[#23]
What? You use a 1-7 twist barrel for self defense? All of my defensive ARs are equiped with a 1-14 twist barrel! 
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Posted: 3/9/2006 2:14:18 PM EDT
[#24]
This is like the razor blade war. All we really need is just go to 1 in 6, 1 in 5, heck, 1 rev per 1". The bullet will open a hyperspace window and go faster than light.
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Posted: 3/9/2006 2:15:02 PM EDT
[#25]
The bullet length part of the equation above refers to total bullet length and does not refer to bearing surface...The Greenhill formula is actually pretty good at predicting bulllet stability in actual field tests.
One point to remember is that overstabilizing a bullet has a much lesser detrimental effect on accuracy than understabilizing it, by several magnitudes, and overstabilization has a negligible effect on a bullet that is symmetrical to begin with. In regards to the original question in the above thread, my opinion is that if one never intends to shoot bullets heaver than 69 grains in that barrel, then a 1/9 twist would be sufficient, but 1/7 would work fine as well. TC |
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Posted: 3/9/2006 2:25:05 PM EDT
[#26]
Silly me, I've shooting everything from 45 to 80 grains from a 1/8 and then a 1/7 without a problem.
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Posted: 3/9/2006 2:36:38 PM EDT
[#27]
You're right!! I just looked up the formula and it does state "Bullet Length" How about when measurueing a Polymer tipped bullet ie: V-Max ect.. for use in the Greenhill Formula, would you measure it "net" (not including the tip) as if it were a hollow point??? +1 Better to over spin than under spin a bullet! They do not leave the barrel stable anyway, but rather need some distance to settle in. Much like throwing a football...., without engouh spin it will never stabilize, but with the right amount of spin, or a little too much spin it will settle into a nice stable spiral. |
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Posted: 3/9/2006 2:53:13 PM EDT
[#28]
For "Spray & Pray" shooting....,  or shooting cans ect... It's pretty much a Non-Issue.But for Surgical shooting  , rate of twist is of measurable importance!!
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Posted: 3/9/2006 2:56:05 PM EDT
[#29]
14.5" bbl is for CQB, get the 1.9 and shoot 55gr FMJs. If you want to shoot past 300-350 meters get a .308! Just my $0.02 do what ever you want!
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Posted: 3/9/2006 3:05:20 PM EDT
[#30]
Formula this and formula that and inherent blah blah blah...
Just kidding, all that stuff is good but I dont think you need to worry with it all. A 1 in 9 is fine for general shooting I think, but some longer or heavier (I think one aids in the other) bullets wont fire accurately out of the 1 in 9 and some lighter loads wont stabalize out of a 1 in 7. If you are wanting range and accuracy I would settle on a bullet and call the manufacturer and ask them what twist would be better for their bullet. But hey, who am I to say. |
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Posted: 3/9/2006 5:25:51 PM EDT
[#31]
Here cry babies. 1in9" gun and target at 100 yards with Blackhills blue box 75 Gr. Quit your bitchin.
  
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Posted: 3/9/2006 6:40:30 PM EDT
[#32]
Really? Do tell! By the way, I was talking about shooting NRA Highpower with those bullet weights from 100 yards (45s) to 600 (75s and 80s). |
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Posted: 3/9/2006 6:47:30 PM EDT
[#33]
Yawn...
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Posted: 3/9/2006 8:34:16 PM EDT
[#34]
I talked to Black Hills about that and they said the 75 grn will stabilize decent out of a 1 in 9 but their 77 grn they said that most people cant pull the accuracy out of it. I was going to get a 1 in 9 barrel but I realy like the 77 grn Mk262 so I went with a 1 in 8, I figure why waste time and money on something that might not work for what I want when I can get something that will work for what I want. |
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Posted: 3/9/2006 8:39:48 PM EDT
[#35]
Not sure I'd be brag'in about that group!! Run some Sierra 63 Gr. Semi-Points through that 1:9 and you should be able to shrink that 100 yard group by half or more!! Here's my pet-load for my 1:9 16" Colt H-Bar II w/Leupold VX-III 4.5-14x40 VH Reticle Sierra 63 gr. Semi-Point #1370 24.5 Grains 2230 Winchester Brass CCI Bench Rest Primer COL @ 2.275" I've had 5-Shot 100 yard groups down to .25" (almost through the same hole) with this load but the groups usually average around .375" on a givin day!! Unless you hand load you can't really expect to get this kind of accuracy unless you really luck into a factory load that your rifle absolutely loves!! Strangely enough my Rem. 700 LV SF 22" 1:12 really loves this particular pet-load as well!! Go figure!! |
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Posted: 3/9/2006 11:28:10 PM EDT
[#36]
www.jimwardrip.com/firearms/556_Ballistics.htm
The increase in projectile length, weight, and configuration of the M855 bullet requires different twists in the barrels, lands, and grooves to stabilize the bullet in flight. The M16A1 has a 1:12 barrel twist (the bullet rotates once for every 12 inches of travel down the barrel). The M16A2/A3/A4 and the M4 carbine has a 1:7 barrel twist (the bullet rotates once for every 7 inches of travel down the barrel). The M16A1, with its 1:12 twist, does not put enough spin on the heavier M855 bullet to stabilize it in flight, causing erratic performance and inaccuracy for training or full combat usage (30.48- to 35.56-centimeter shot group at 91.4 meters and 72-inch shot group at 274.2 meters) (Figure 2). Although firing the M855 cartridge in the M16A1 rifle is safe, it should only be used in a combat emergency, and then only for close ranges of 91.4 meters or less.  Figure 2. Ammunition impact comparison. The M16A2 rifle with its 1:7 twist fires both types ammunition with little difference in accuracy to a range of 500 meters. The M16A2 and its ammunition are more effective at ranges out to and beyond 500 meters due to a better stabilization of the round. The two 10-round shot groups in Figure 2, A were fired by a skilled marksman at a distance of 274.2 meters using the same M16A1 rifle. The 25.4-centimeter shot group on the left was fired (and zeroed) with M193 ammunition. The 6-foot shot group on the left was fired with M855 ammunition. Figure 2, B shows two 25.4-centimeter shot groups fired by the same skilled marksman at a distance of 274.2 meters using an M16A2 rifle. The shot group on the left was fired (and zeroed) with M855 ammunition. The shot group on the right was fired using M193 ammunition. As stated previously M193 and M855 ammunition can be fired from an M16A2-/A4-series weapon. Table 1 and Figure 3, show the difference between a rifle zeroed with M855 ammunition and then re-zeroed with M193 ammunition at 300 meters. There is practically no difference between the trajectory of the rounds or the impact of the rounds on target. |
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Posted: 3/10/2006 5:07:46 AM EDT
[#37]
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Posted: 3/10/2006 5:23:27 AM EDT
[#38]
Bushmaster has stated that their 1/9 twist barrels (20" and longer) will stabilize 73gr-75gr bullets. Anything heavier will require 1/7 twist. I think they even state that their 16" and shorter barrels in 1/9 twist will stabilize up to 69 gr.
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Posted: 3/10/2006 12:21:46 PM EDT
[#39]
The higher the muzzle velocity, the faster the bullet spins...therefore less twist is required for stability. As you can see from the posts here...the 75 gr is right at the upper limit for 1/9...it's worth a try though.
TC |
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Posted: 3/10/2006 1:18:14 PM EDT
[#40]
Add my anecdotal experience, with a total of 7 barrels: 1/9 shoots 55gr slightly better than 1/7 at 100 yds. Statistically insignificant, but if you have a stash of 5k rounds of 55gr, keeping a 1/9 barrel around is perhaps a good idea.
RU4Freedom, if all, or even most, chromelined Colt HBAR 16in barrels shot .375in, there would be no market for Krieger/Noveske/Lilja. You must have an extraordinary barrel. Would you come to Vegas with me? |
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Posted: 3/10/2006 3:03:31 PM EDT
[#41]
It is a Garden Variety Colt Match Target Comperition H-Bar II & is Chrome chamber only, no chrome bore! The only things I have done to it is a Free Float tube, Accuracy Speaks FCG w/ KNS Oversize pins, Hogue Grip & I tighten the Upper/Lower fit w/some Accuraglass. other than that it is bone stock!! But it does indeed have that "one in a million" barrel that seems to be leaps & bounds more accurate than most other AR's. I've had more than one guy at the range poke fun @ my "Little Carbine" until he finds himself holding an empty wallet after paying out on a lost bet against my "Little Carbine" for accuracy!!! I do have to take a little credit for myself......, afterall......, there is a certian amount of benchrest discipline & consistency involved!! This was actually the first AR I ever bought & will never give it up...., for obvious reasons!! It's really kind of funny how things worked out! At first I couldn't get a decent group with this Colt no matter what I fed it, factory or handloads, heavy or light bullets nothing seem to work out! So I started experimenting with bullet seating depth to see how close I could get the bullet to contacting the rifling lands in full battery, but still be able to have a COL short enough to ft & feed properly from a AR Mag. Long story short the only bullet I could find that fit the bill was the Sierra 63 gr. Semi-Point #1370 The unique ogive of this particular bullet tapers off so fast that when seated out to 2.275" it comes within a couple thousands from touching the Colt's rifling lands in full battery. A few differant powders & charge weights later & bingo it all came together!! Sorry for the long winded post..., but as you can tell, I really love this "Little Carbine"!! By the way...., what's in Vegas??? |
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Posted: 3/10/2006 3:46:00 PM EDT
[#42]
Quoted:
You tring it with both eyes closed. LOL. I am not bragging I am just showing it can be done with a 1in9" and 75 gr. Alot of people dont think it can be done and I will never use homemade reloads in a AR. I have seen to many KABOOMS with reloads ,Thank U. It shoots real well with the 45 gr Winchester Value packs too. -------------------------------------------------------------------------------------------------------------------- Point taken....., without your example I too would have had doubts about a sub minute 100 yd. group with 75 gr. pill through a 1:9" |
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Posted: 3/10/2006 4:05:38 PM EDT
[#43]
1/7 shoots everything well enough. If I need great accuracy with 55gr bullets I might get a 1/12 barrel, but the only 55gr I shoot is surplus shit anyway, so I don't care. 1/9 offers me NO advantages.
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Posted: 3/10/2006 6:48:13 PM EDT
[#44]
Now the truth is starting to come out. Doesn't "bench rest discipline" call for careful finger loading of those "special" rounds. Surely you don't feed those rounds through the mag, and chute grinders? Apologies to the off-topic police, but this anecdote appeals to me more than rehashing all those 1/7 vs. 1/9 urban legends. |
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Posted: 3/11/2006 6:26:51 AM EDT
[#45]
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Posted: 3/11/2006 9:48:31 AM EDT
[#46]
Absolutely!! Not only that, but each & every round I load gets the exact same treatment including a maticulous hand polishing of the bullet since my bullet choice has an exposed lead tip. When shooting for groups, the only thing my rounds contact is the chamber itself!! To me the whole idea of punching paper is to eliminate as many variables as possible, so that when Varmint & Predator hunting I only need to consider atmospheric, wind & other natural conditions, ect.... When predator hunting I do feed the rounds through a magizine. But so far very few Coyote's out to & including 500+ yards have survived to tell their story!!  -----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------Punching paper is just the "Homework" The test for me is taking Critters @ long range . I'm an avid Upland Bird hunter. My brother & myself spend most of the off season doing our part to keep the Predator count as low as possible in our upland areas. Last weekend I put down two coyotes, one @ 523 yards & his partner & 444 yards!! My brother got three from 80 to 300 yards with his bolt gun. Any of you guy's that Upland Game hunt in Eastern Washington that has noticed the Upland game population on the rise......., your welcome!! |
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Posted: 3/11/2006 10:19:09 AM EDT
[#47]
A---------men Brother!!! 
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Posted: 3/11/2006 11:53:42 AM EDT
[#48]
As long as habitat is conducive to good nesting and breeding, predator control is effective. Otherwise, nothing you do will matter. |
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Posted: 3/11/2006 5:28:58 PM EDT
[#49]
We sure have hijacked the sh*t out of this thread...., unintentually!!!
Sorry tucansam Anyway...., the areas I bird hunt in are mostly public lands that have awesome nesting habitat, feed, water & escapement!! But over the years, since about the late 70's we have seen a steady decline in bird populations along with an increased number of predator kills that we have found. That combined with weather conditions that are not always condusive to productive nesting & good hatches!! There is nothing we can do about the weather...., but we are doing our best to put a hurt on the predator population!! There is a pretty heavy kill by hawks as well, but as far as I know they are protected in Washington. Some of our best upland hunting areas are controled by the "Federal" Wildlife (not State, but Feds) and are closed to Predator hunting. Most of these areas have awesome upland habitat but are over run with Coyotes & Bobcats!! I have tried to get the Feds to have a "Predator control" hunt in these areas but they refuse to allow it. Needless to say we now have several locations just outside the perimeters of these "Closed" areas that have turned out to be very productive for calling in Predators to their demise!! |
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Posted: 3/12/2006 3:22:15 AM EDT
[#50]
Please describe the finger loading process. Bolt locked back, empty mag inserted, etc?
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