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Centerfire Rifles - Semiautomatic or Gas Operated Centerfire rifles, carbines and other gas operated rifles.

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  #1  
Old 11-06-2011, 3:40 PM
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Default 1/7, 1/8, or 1/9 twist with which ammo?

So I've been told that 1/7 is better for heavier rounds (60-75gr) and I have no idea if someday I might want to shoot long range. Curious if most of you can find the lighter ammo (45-55gr) cheaper ammo and just use a 1/7 or 1/8 twist which might be lighter ball and perhaps lighter recoil as I heard using a 1/9 twist with heavier ball is not as accurate and vice-versa using 1/7 twist with a lighter ball is not as accurate.

Any thoughts?

Or do you all just get a couple of rifles....one for the lighter and one for th heavier...
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  #2  
Old 11-06-2011, 3:42 PM
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Google please. This has literally been talked about 100 times on at least 5 differant forums. With the same exact answers. And all of the same people show up to debate it.
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  #3  
Old 11-06-2011, 3:52 PM
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http://www.ar15.com/content/page.html?id=493

scroll down to the twist section.
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  #4  
Old 11-06-2011, 4:05 PM
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Where is Deiselpower, his info needs to be stickied.
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  #5  
Old 11-06-2011, 6:53 PM
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Not heavier weight, longer bullet design.

75gr bullet .224 lead will be same length as a 55gr solid copper .224.
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Old 11-06-2011, 7:18 PM
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1/8 seems to be the best compromise if you plan on shooting both heavy and light bullets. Not so fast that you'll disintegrate the lighter varmint loads, but fast enough to stabilize the heavier bullets.

As mentioned, this is kind of like the "Chevy vs Ford" argument, but there is a lot of sound data and discussions if you look around. Google it here and on many other forums and shooting reference sites.
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  #7  
Old 11-07-2011, 6:38 AM
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Quote:
Originally Posted by kjgun View Post
So I've been told that 1/7 is better for heavier rounds (60-75gr) and I have no idea if someday I might want to shoot long range. Curious if most of you can find the lighter ammo (45-55gr) cheaper ammo and just use a 1/7 or 1/8 twist which might be lighter ball and perhaps lighter recoil as I heard using a 1/9 twist with heavier ball is not as accurate and vice-versa using 1/7 twist with a lighter ball is not as accurate.

Any thoughts?

Or do you all just get a couple of rifles....one for the lighter and one for th heavier...
I count 25 times in about 8 months - search is your friend.

Perhaps the admins will take pity and sticky this response so we don't have to keep doing this.

http://kwk.us/twist.html

Note the inputs are: Length, Diameter, Velocity and Specific Gravity.

For example:

* 77 grain lead core scenar projectile is 1.010" long
* .224" diameter
* 2800 FPS
* SG is 11.3

This gives a result of 9.4"

Calculating for a 90 grain LVD results in 7.6" which can generally be rounded up to 1:8"

Bearing surface adds a lot more variables for the specific projectile design that aren't included. Also factors such as temperature, elevation, humidity (air density) and so on are important to long range bench rest shooters, but not as demanding for someone with a plinker.

R
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Old 11-07-2011, 7:05 AM
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people need to copy these charts I make and post them when needed...photobucket is going to start charging me for bandwidth lol

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Old 11-07-2011, 8:35 AM
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Nominate Diesel for a sticky !!!!!!!!!
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  #10  
Old 11-07-2011, 9:09 AM
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Quote:
Originally Posted by dieselpower View Post
people need to copy these charts I make and post them when needed...photobucket is going to start charging me for bandwidth lol

The one problem I have with the chart is that it assumes the projectile specific gravity (the metallic element constituting the core and jacket) is a constant, not a variable. If all the projectiles were lead cored, the chart would coincide with the calculations that you made to create it. If the projectiles were of a lower mass (say, 100% copper) the length would dramatically increase and the twist necessary to stabilize such a long projectile would be wrong, even though the lead core and the all-copper projectiles might have identical weight. This is why I would prefer to see more emphasis on the length of the projectile instead of weight.

R
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  #11  
Old 11-07-2011, 10:44 AM
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FWIW, my 1:9 Varminter shoots 69g SMK better than all other weights, according to this graph that should not be the case. User results may very.
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  #12  
Old 11-07-2011, 11:03 AM
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Quote:
Originally Posted by Richard Erichsen View Post
The one problem I have with the chart is that it assumes the projectile specific gravity (the metallic element constituting the core and jacket) is a constant, not a variable. If all the projectiles were lead cored, the chart would coincide with the calculations that you made to create it. If the projectiles were of a lower mass (say, 100% copper) the length would dramatically increase and the twist necessary to stabilize such a long projectile would be wrong, even though the lead core and the all-copper projectiles might have identical weight. This is why I would prefer to see more emphasis on the length of the projectile instead of weight.

R
its a "talking points chart" not a bible page or a formulated theory on ballistics. This is for the general shooter, not the scientist nor the SEAL sniper student....

If you want to get all technical you need to factor in; type of powder, type of barrel steel, shape of projectile, muzzle crown, muzzle device, length of barrel (whip)..and all those calculations would be subjective is as the outcome would depend on outside conditions such as air temp, air mass, relative humidity, elevation and direction N,S,E,W of projectile travel...

as a general rule my chart works.. I have a 1:9 and shoot MK262 Mod1 just fine, I know I would have better results and better groups with MK318. I can shoot .223 55gr federal bulk FMJ too...and so could a guy with a 1:7 twist. The only guys who really need to freak out on this stuff are the guys who know who they are... a SEAL or SWAT sniper isn't going to be asking this question on this forums board
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  #13  
Old 11-07-2011, 12:15 PM
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Quote:
Originally Posted by dieselpower View Post
its a "talking points chart" not a bible page or a formulated theory on ballistics. This is for the general shooter, not the scientist nor the SEAL sniper student....

If you want to get all technical you need to factor in; type of powder, type of barrel steel, shape of projectile, muzzle crown, muzzle device, length of barrel (whip)..and all those calculations would be subjective is as the outcome would depend on outside conditions such as air temp, air mass, relative humidity, elevation and direction N,S,E,W of projectile travel...

as a general rule my chart works.. I have a 1:9 and shoot MK262 Mod1 just fine, I know I would have better results and better groups with MK318. I can shoot .223 55gr federal bulk FMJ too...and so could a guy with a 1:7 twist. The only guys who really need to freak out on this stuff are the guys who know who they are... a SEAL or SWAT sniper isn't going to be asking this question on this forums board
Point taken.

R
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  #14  
Old 11-07-2011, 1:12 PM
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+1 on a diesel sticky.


The military standard issue firearm is 1:7, so what is the standard issue bullet weight length? is it 55g? that just seems to be the most common out there...

with a 1:7 twist i'd think theyd issue 69g +
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  #15  
Old 12-09-2011, 6:05 PM
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Quote:
Originally Posted by jacobIDSC View Post
+1 on a diesel sticky.


The military standard issue firearm is 1:7, so what is the standard issue bullet weight length? is it 55g? that just seems to be the most common out there...

with a 1:7 twist i'd think theyd issue 69g +
I hate to kick this thread to the top, but....

the reason military is using 1:7 is because (from what I understand) they have to stabilize the tracer rounds, (they are much longer) also the military uses M855 62gr these have a steel core thus the bullet is much longer than 55gr because of the steel core (lead weighs more that steel so when you add steel in a bullet you have to add more lead to make the weight) so all in all it's more about the length of the bullet than the weight.
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  #16  
Old 12-09-2011, 6:52 PM
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A couple of days ago, I was buying a bunch of 62gr 5.56 ammo and the clerk asked me why I was buying that and not the (similarly priced) 55gr .223 "since most people buy that."

I replied, "because the twist on my AR barrel is 1:8," and he looked at me with a completely confused expression on his face, so I added "I like it better" and the clerk relaxed and smiled and sold me the ammo.
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Old 12-09-2011, 7:47 PM
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^ isn't that special....
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Old 12-09-2011, 9:16 PM
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Originally Posted by nani View Post
A couple of days ago, I was buying a bunch of 62gr 5.56 ammo and the clerk asked me why I was buying that and not the (similarly priced) 55gr .223 "since most people buy that."

I replied, "because the twist on my AR barrel is 1:8," and he looked at me with a completely confused expression on his face, so I added "I like it better" and the clerk relaxed and smiled and sold me the ammo.
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Old 12-10-2011, 10:21 AM
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Quote:
Originally Posted by dieselpower View Post
people need to copy these charts I make and post them when needed...photobucket is going to start charging me for bandwidth lol

I'm hate to say it, but the chart is off. One, it's length not weight of the projectile that determins twist rates and two, an 80gr VLD (a very long bullet) stabalizes great form a 1/8 twist barrel. The 1/7 twist is really only optimal if you want to go really heavy up to 90gr lead core bullets or an equivalent length projectile. Having more twist than you need is not neccisarily detrimental, but it raises pressure and lowers velocity.
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Old 12-10-2011, 10:23 AM
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Berger has a list of 223 bullets and the reccomended twist rates. Keep in mind that the vld type bullets are even longer than most other lead bullets of equal weight.
http://www.bergerbullets.com/Product...20Bullets.html
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Old 12-10-2011, 10:28 AM
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Originally Posted by chicoredneck View Post
I'm hate to say it, but the chart is off. One, it's length not weight of the projectile that determins twist rates and two, an 80gr VLD (a very long bullet) stabalizes great form a 1/8 twist barrel. The 1/7 twist is really only optimal if you want to go really heavy up to 90gr lead core bullets or an equivalent length projectile. Having more twist than you need is not neccisarily detrimental, but it raises pressure and lowers velocity.
We all know it's length. That's been said a dozen times in this thread alone. Diesel even said so, and he's right about there being a lot of other variables too. Fact of the matter is, for 95% of shooters (and probably 99.999% of starting shooters) this chart will answer their questions.
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Old 12-10-2011, 11:11 AM
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Originally Posted by Reductio View Post
We all know it's length. That's been said a dozen times in this thread alone. Diesel even said so, and he's right about there being a lot of other variables too. Fact of the matter is, for 95% of shooters (and probably 99.999% of starting shooters) this chart will answer their questions.

Of course it will answer their questions, it just answers it incorrectly in a number of ways. I have seen this chart posted a number of times and held my peace. I do not mean to bash the creator of the chart, but it is partially false information. I love the internet and the wealth of information it holds. Unfortuanetly navigating the internet is like navigating a mine field of good and bad info. If you do not know what to look for you can start believing and utilizing incorrect information/data. That is why I posted the link that I provided. It is actual information from a bullet manufacturer. Their recommended twist rates are going to be far more accurate than some chart than was posted by someone whose credentials may not be verifiable. I do not mean any disrespect to anybody and especially dieselpower. I'm just trying to provide accurate data for the OP and the readers of this fantastic forum.

http://www.bergerbullets.com/Product...20Bullets.html
Bryan Litz is a renowned balistician who works for berger bullets. The info posted on their website is some of the most accuate I have found.
https://www.sierrabullets.com/index....ge=items&cat=8
scroll over important information for twist recommendations

Last edited by chicoredneck; 12-10-2011 at 11:23 AM..
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Old 12-10-2011, 11:11 AM
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Quote:
Originally Posted by Reductio View Post
Fact of the matter is, for 95% of shooters (and probably 99.999% of starting shooters) this chart will answer their questions.
I agree. Before I picked up my AR this week, I found this chart very helpful when I was researching what ammo to buy as it relates to my specific AR profile. I know I can throw almost any 5.56 ammo in my AR and it will work fine, but this chart helped me understand why I may not be as accurate with a certain ammo.
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Old 12-10-2011, 11:16 AM
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Originally Posted by chicoredneck View Post
If you do not know what to look for you can start believing and utilizing incorrect information/data. That is why I posted the link that I provided. It is actual information form a bullet manufacturer.
I appreciate you providing that link. I'm new to ARs myself, and in researching ARs and ammo, I found that different manufacturers can have very different standards, which is why so many competitive shooters reload their own for accuracy.

Edit: accidentally a word.

Last edited by nani; 12-10-2011 at 12:27 PM..
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