# A question about ammo and twist rate



## budgetprepp-n (Apr 7, 2013)

Ok I have a question about twist rate and ammo 
If an AR with a 1-to-7 calls for a 62gr what would a 1-to-9 call for?
And how dose it work? More twist rate calls for a lighter round?

It's so nice to ask basic questions on line so you don't look stupid in person. 
One thing I'm getting at is a 62gr OK for a 1-to-9 

This is where someone says "I wondered about that also" so I don't look bad


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## Fuzzee (Nov 20, 2012)

The faster twist rates are designed to better stabilize heavier grain bullets and the slower, lower grains. Regardless, both twists in an AR will shoot the different grains, just one better than the other. You still have to take into mind if squeezing maximum accuracy is important to you that all barrels aren't exactly the same down to the smallest aspect of the bores surface, chamber and muzzle, and some barrels shoot better than others of the exact same spec and make. You've got to find what yours likes and shoots best.



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## AquaHull (Jun 10, 2012)

1 in 9 was designed for the 62 gr SS109 bullets,called M855, also called steel penetrator

1 in 7 was designed for the 64 gr FMJ tracer bullet called M856

1 in 7 can overstabilize the 62 gr bullet leading it to not work the way Eugene Stoner designed the platform. In fact the SS109 was not around then.

Knowing this,I'm switching out to mostly 1 in 7 twist barrels since it seems the better barrels are 1 in 7 , and I shoot mostly 55 gr FMJBT at paper.

One barrel marked 1 in 7 twist may be similar to one marked 1 in 9 twist since manufacturers processes are different and the markings are sometimes a guess or a wish.

Enjoy finding out for yourself and stay safe.The more you find out,the more you will wish you didn't know. I say KISS, buy what you want ,most any twist will shoot the 55 gr bullets.


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## AquaHull (Jun 10, 2012)

More of what you might need or not need to know

AR15 Ammo Forum FAQ - AR15.COM


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## Notsoyoung (Dec 2, 2013)

Here is a chart of the Maximum bullet weights that you should use with the different twist rates:

Barrel Twist Rate: 1:14”| 1:12” | 1:9” | 1:8” | 1:7” or 1:6.5”
Max Bullet Weight: 55 gr FB| 65gr FB| 73gr BT | 80gr BT | 90gr BT VLD


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## LunaticFringeInc (Nov 20, 2012)

Im not a rocket scientist, but I have played around with this subject in 22 cal centerfire rifles quit a bit as I have a custom Mauser 98 in 224 TTH. For that gun the primary bullet weight was going to be 77-85 gr bullets. Me and the builder settled on 1-6 twist rate which seems to be the cats meow for what we wanted to achieve with hat build.

I recently got a Mossberg MVP in 5.56. I tested it with a wide variety of ammunition loads and bullet weights. Here is what I found. With the 1-9 twist rate the barrel has I got excellent results from 53 gr all the way up to 69 grs. Below 53 and the groups looked more like shotgun patterns with 00-buck than they did rifle groups. In fact some of the 55 gr groups started to look a little shabby depending on the bullet brand in question. Above 69 grs and the groups started to progressively open up considerably as the bullets got heavier and longer. Between 55-69 grains this gun grouped very well, giving sub MOA 5 shot groups more times than not with several going into 1/2 MOA or slightly less with boring regularity. The best group was .38 inches with a 62gr Swift Sirroco II( which for a 62 gr bullet is a very long and aerodynamic bullet with high BC numbers)!!! Yes that was 5 shot groups at 100 yards on an outdoor range...

What I have found is that its not the bullet weight as much as it is the length of the bullet in question, more specifically the length of the bearing surface that will engauge the rifling to be more specific. For example the short stubby 60 gr Nolser Partions will usually do well in 1-12 twist guns that most varmint oriented guns have. When Nosler designed this bullet they designed it in mind that many would be shooting in such barrels and the bullet was designed to stabilize adequately. It also needed to hold together and penetrate enough to make humane kills on smaller Deer like we have in Texas or Florida for the most part. The 64gr Winchester Power Point attempts to achieve the same thing but goes about it in a different way bullet construction wise than Nosler did. The 64 gr Power Point will test the outer limits of a 1 in 12 twist barrel though due to its length more so than the Nosler. The 77 gr Swift Sirroco II in the 77 gr load will almost certainly require a 1-7 twist rate and possibly give even better results in a 1-6 Barrel.

The optimal barrel twist rate is a combination of velocity, barrel length or lack there of as well as bullet length, the latter quality being the bigger factor of the three.


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## AquaHull (Jun 10, 2012)

The further you dig into this subject, the deeper it gets.


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## LunaticFringeInc (Nov 20, 2012)

Yes it does Aquahull. By the time I chose the specs on the 28 inch barrel for my 224 TTH (80gr bullet at 3750 fps at the muzzle) , I felt like I had a Phd in Physics and had, had a baby too! I am surprised there was any hair left on my head by the time it was all said and done and the details carefully worked out. Its definitely a balancing act.


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## jimb1972 (Nov 12, 2012)

1 in 7 or even 1 in 9 is going to work good enough for anything you can get in an AR mag. Unless you are scoring your targets at over 300 meters it really does not matter, I have 75gr HPBT that I have fired out of a 1in9 barrel and they all go into 3" at 100 yards and thats with open sights. Unless you are doing benchrest competition I think a lot more is made of the barrel twist rates than is really necessary.


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## PrepConsultant (Aug 28, 2012)

There is so much you can go into on this subject it isn't funny. These guys have all given good info. I am a stickler for twist rates. I shoot for extreme accuracy so i want the best combination for what I am doing. We have several AR's in different configurations/barrel length/type and twist rates. My 308's I pay even more attention to it because of shootinglonger range. So far my favorite combination for a 308 bolt rifle is a 20in bull barrel with a 1/10 twist shooting a 175/200 and 220gr pill.. Depending on what range I am shooting. I just heard the other day actually that the Marines are going to the 20bbl with 1/10 twist on their new rifles.. I am building another 308 and having a Krieger 20in bbl with a 1/8.5 twist, so we'll see how it does. I have a friend that has one and it shoots 1/4 moa and better.. I have always loved bull barrels and when you run a 20in bbl or even 18in you take a lot of weight off and still have the accuracy..


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## rickkyw1720pf (Nov 17, 2012)

A 55 gr bullet shot out of a ar-15 with even a 1-12 twist spins at 180,000 rpm. Its almost unbelievable that the centrifugal force doesn't spin the jacket off.


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## AquaHull (Jun 10, 2012)

I was thinking of getting that pre-owned 1 in 12 20" Colt barrel for fun


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## PaulS (Mar 11, 2013)

The one thing that I have learned is that if you want to shoot heavy and light bullets in the same gun go for the tightest (fastest / lowest number) twist you can get. 

My 358 has a 1:10 twist so I can shoot 250 grain bullets with it but it also shoots 158 grain pistol bullets to .33 inches center to center at 100 yards. If I was only going to shoot 158 grain pistol bullets a 1:17 twist would be just fine but if you are going to shoot long bullets (regardless of weight) then you need a fast twist. My 3006 will shoot any bullet from 100 grains to 200 grains but it will not shoot a 220 grain bullet - they go into a 100 yard target sideways. If I could get a 1:7 twist for my 3006 I would!


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## Montana Rancher (Mar 4, 2013)

AquaHull said:


> 1 in 9 was designed for the 62 gr SS109 bullets,called M855, also called steel penetrator
> 
> 1 in 7 was designed for the 64 gr FMJ tracer bullet called M856
> 
> ...


I respectfully disagree, the 1:7 is used for the 55 grain bullet, with stunning success.


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## Montana Rancher (Mar 4, 2013)

LunaticFringeInc said:


> What I have found is that its not the bullet weight as much as it is the length of the bullet in question, more specifically the length of the bearing surface that will engauge the rifling .


I totally agree.

I shoot Barnes X bullets which are solid copper and as a result MUCH longer than a comparable lead bullet with a copper jacket.

So a 180 grain 30-06 bullet is shorter than a 150gr Barnes X

And a 100 grain .243 is shorter than a Barnes x 85 grain bullet.

I have found that the lighter Barnes bullet is more accurate than the heavier composite bullet and since I have more velocity, has more "knock down power" than the traditional bullet.

My experience with heavier Barnes X bullets is they don't shoot worth a shit, for instance a 200 grain .308 bullet is a crappy assed excuse for a bullet, if anyone wants some let me know I have a couple hundred to sell.


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