What is the heaviest load a 1:9 twist barrel can handle in .223?

K

Kimio

New member
Looking around and reading some threads, I just wanted to make sure I got my facts straight.

I am looking into getting an AR15 with a 1:9 twist 20" barrel, so far from what I've read from elsewhere is that this twist rate is ideal for the 55gr to 70gr loads of .223

If I wanted to go for heavier loads I would probably want to look into a 1:8 or even a 1:7 twist barrel. Since I will most likely not being getting into any competition or match shooting anytime soon, I will most likely be shooting the 55gr stuff for practice at the range. However, I do eventually want to get into competitions, should I look into the middle of the road twist rate for my AR, the 1:8?

What should I expect from this, I've read that the faster twists may actually be detrimental to the performance of lighter loads, is this true? In the event I would want to upgrade from a 1:9 twist to a faster twist ratio, how hard would this be to accomplish? I don't think I would have to buy a new upper seeing as how many if not all AR models can be assembled from parts. ranging from assembled to stripped uppers and lowers.
 
Mine will shoot 69gr. with no problem. I have shot some 75gr. as well, but choose to stick with the 69gr. and under. I reload 55,60,65, and 69gr. for my mini. I think you will be fine with 69gr. If I was you I would try 75gr. and see how your rifle shoots them.
 
My 16" Bushmaster HBAR shot about 4-5" 5rd groups at 100yds with Black Hills Match ammo in 75gr (Hornady) and 77gr (Sierra).

My friend's 16" Armalite 1:9 HBAR shot the same ammo into about an inch at 100yds.

Some people seem to have no trouble shooting the heavier ammo out of their 1:9; however having personally experienced it and read a fair amount of reports of other people having that problem, I would say that if you know you want to use heavy ammo, you should go with something faster than 1:9 since even the ballistics programs show 1:9 as being marginal at best for stability of heavy rounds.
 
You may find this helpful.

50923489.jpg
 
Each rifle is unique. Each one likes and dislikes it's own list of bullets and ammo. If someone tells you that 1:7 will do these bullets and 1:9 WILL do these bullets; then they are quite "Mistaken".

There is only 1 way, and 1 way ONLY, to say what a particular rifle will shoot accurately. That's to shoot it. And while you're at it, you'll find that it can do well with 1 brand of ammo, and not as well with a different brand in the same bullet weight. And that's the same no matter what the weight it. I.e. My 1:9 S&W M&P15 is the most accurate with 62grain bullets. Much better than 55 grain. But I have shot 75 grain bullets out of it. "It's not like there's some law that say you're not allowed to shoot a 75 grain in a 1:9 barrel; or that it will blow up or something". Shooting some steel case russian ammo in 75 grain; I was still able to shoot in the 4" block open sight that I use for all ammo. In other words; if the 75 was "LESS RELIABLE" compared to 62 or 55 grain; it was negligible. Now; if you're shooting 300 yards, it would probably be more noticeable. But at 100 yards it worked fine.

So; the only way to know for sure, is to try it. And, you'd have to try different brands of ammo. It can shoot great with one brand and not as great with another. But anyone saying that the 1:9 shouldn't shoot anything above 69 grains, is simply guessing.

And for what it's worth, the bullet weight has absolutely nothing to do with it. it's the "LENGTH" of the bullet. It just so happens that a LONGER bullet generally weights more, but it doesn't have to. That's why you can only be sure by shooting each ammo for yourself.
 
Nice Venn diagram, madcratebuilder!
Allow me to touch it up a bit, so that no one gets left out...
~Dan

venn.jpg
 
I believe that it's the rpm of the bullet that actually does the stabilization.

It all starts with the barrel twist rate + speed of bullet. If I'm not mistaken that would mean that if a bullet went through a barrel with a 1/10 twist rate in 1 second it would be spinning at 10 revolutions a second, but if the same bullet went through the same barrel in half a second it would be spinning at 20 revolutions a second (more stable for heavier bullet).

Then again I could be wrong.
 
Its down to actually shooting it. Nuthing will help you more at this point.


abarhorst: Please dont take this the wrong way, but it would be good if you studied the subject a bit more. It is kinda complicated and for sure confusing if not applied correctly. Search "Miller Stabilization". And Win-Gyro.

christcorp
And for what it's worth, the bullet weight has absolutely nothing to do with it. it's the "LENGTH" of the bullet. It just so happens that a LONGER bullet generally weights more, but it doesn't have to. That's why you can only be sure by shooting each ammo for yourself.
Click to expand...
Click to expand...

This is what its all about.



The chart posted above should only be referenced as a loose guide. There is too much room for overlaps in some barrels to limit one experimentation to that chart.

Since the OP is not up and reloading as of yet. I would advise testing with the highest quality ammo that you can afford to shoot enough to get real results.



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This is what it boils down to:
abarhorst said:
I believe that it's the rpm of the bullet that actually does the stabilization.
Click to expand...
christcorp said:
And for what it's worth, the bullet weight has absolutely nothing to do with it. it's the "LENGTH" of the bullet. It just so happens that a LONGER bullet generally weights more, but it doesn't have to. That's why you can only be sure by shooting each ammo for yourself.
Click to expand...

These two concepts are why a .220 Swift with a 1:14" twist barrel can shoot 55 gr FMJs into clover-leafs all day long, while the .223 next to it will be shooting shotgun patterns.

It's all about RPM. The .220 Swift uses a slow twist rate, and high muzzle velocity; while .223 Rem uses a fast twist rate, and low muzzle velocity. And, different bullets require different RPM to stabilize.

As several posters have pointed out: Every barrel is different. And, running in an AR, your muzzle velocity will be lower than "optimal". Which means you'll probably have to shoot at least one weight bracket lower than predicted.
 
RPM are a big factor but other factors are:

air density ( low elevations have higher density, cold air is denser) Low density facilitates projectile stability

bullet length, longer bullets need higher RPMs to stabilize ( for a given weight some bullets are longer than others) think barnes copper vs jacketed soft points
 
Nice Venn diagram, madcratebuilder!
Allow me to touch it up a bit, so that no one gets left out...
~Dan
Click to expand...

I like the update on the chart. I've found that with AR barrels they are not always exactly the twist rate they are marked. A 1-9 marked barrel could be 1-8.6 or 1-9.4. There have been many threads were members have measured twist rates, and found a substantial difference from what's marked. That info would be nice in a chart. I'll wipe that right up, in my free time:D
 
All the charts shown, and they are good starts, are only starting points.

While the barrel twist determines the bullet spin rate, the balance between the stock and the barrel add a critical variable that makes every rifle different.

Even if the barrel twist is identical from rifle to rifle with the same twist rating (and I don't believe for a second that twist ratings guarantee the twist of your particular barrel), when you mate the barrel to the stock you have just changed everything. Of course if the barrel is thin or heavy also has lots to do with the accuracy that is possible with a particular rifle.

Trying to aim a rubber hose when you turn on the water while holding the hose a few inches back from the nozzle may give you an idea of the kind movements that a barrel will make when it gets pulsed with an explosion of powder against the bolt face that propels a slightly oversized bullet down a rifled barrel. The barrel oscillates and vibrates at the same time. The degree of either is determined by the magnitude of the shock applied (powder load), the length of the bullet and its shape (how much of the bullet actually touches the rifling), and the way the barrel mates with the stock. If there is any place where the vibration or oscillation can be damped by touching, the barrel / stock combination will do strange things to accuracy.
If they don't do exactly the same thing every time, accuracy really suffers.

Because every rifle is different when it comes to the barrel/stock combination, all the posters who say you have to shoot your own rifle and experiment with it are absolutely right.
 
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