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riggins_83
May 27, 2009, 08:19 PM
I intend to do some varmint hunting and use up some of my 223 55 grain Remington VMC in the process. I can just about guarantee I'll never shoot anything but 55 grain 223 ammo.

From what I've read this is right on the line for weight class and either twist will handle it. The question is which rifling will have the edge? All my shots will be 150 yards or less.

Skyyr
May 27, 2009, 08:27 PM
If you'll never shoot anything but 55-grain, then a 1/9" is preferable. Most recreational and varmint AR's are set up with a 1/9" twist to accommodate the lighter rounds.

You only need a 1/7" when shooting the heavier bullets, such as the M855 Ball, which is the ammo designated to be used in M4's/M4 Clones (which is why they have 1/7"). Match rifles are commonly set up with a 1/8" to provide an "all-around" for handloading and a wider range of rounds.

The heavier a .223/5.56 bullet, the longer it is. The length of the round determines the twist rate. Longer rounds require faster twist rates to stabilize.

Dallas Jack
May 27, 2009, 11:56 PM
I don't mean to Hi-Jack your thread but I was wondering what weights a 1:12 twist would handle.
Dallas Jack

Scorch
May 28, 2009, 12:11 AM
55 gr bullets typically shoot best with a 1:12" twist in a 223. 1:9" is for bullets up to 70 gr or so, 1:7" is good up to 85 gr or so.

kiwi56
May 28, 2009, 12:47 AM
Scorch just what I was going to say, you should only be looking at 1:8 or 1:9 if you are shooting bullets over 70 gains. On my 223 Ackley I have a 1:12 twist and this gives best accuracy with 55 grainers (typically 1/2 MOA) although it is still sub MOA with 60 grainers but go to 69 grains and groups open up to about 1.5 MOA.
In days gone by most factory twists were around 1:14 but this was only okay up to about 50 grainers.
The danger with handloads approaching Maximum in these fast twist 1:8 & 1:9 barrels is that pressures can rise very quickly.

qwman68
May 28, 2009, 01:56 AM
my ruger has 1-9 twist and it will shoot ip to 75 gr. it shoots the best with 69 gr.

Skyyr
May 28, 2009, 09:38 AM
@Scorch

I almost suggested a 1/12", but that's borderline. A 55-grain is the heaviest bullet you can shoot reliably with a 1/12, whereas a 1/9" can handle 40-75 grain, with 55-65 being the seeming range of optimal round weights.

A 1/12" is better suited for 40-55 grain. Unless he plans on shooting super-lightweight loads (< 50 grains) on a regular basis, he'd be better suited to the more universal 1/9".

Just my .02

mikejonestkd
May 28, 2009, 09:51 AM
@Scorch

I almost suggested a 1/12", but that's borderline. A 55-grain is the heaviest bullet you can shoot reliably with a 1/12,

It all depends on the barrel length and muzzle velocity. The OP did not specify the rifle that he is using. A shorter 16" AR platform .223 would need a faster twist than a 26" bolt .223.

I find that with my .223 rifles I can get great accuracy up to 62 grainers with one in 12 twist out of a 26" barrel.

Dood_22
May 28, 2009, 09:53 AM
If you have a rough-throated or low quality 1/9 and shoot fragile varmint bullets like the SX and Blitz, you will have bullets disintegrate in flight.

For light, fragile bullets, I would recommend a 1/12.

Alleykat
May 28, 2009, 10:18 AM
If you have a rough-throated or low quality 1/9 and shoot fragile varmint bullets like the SX and Blitz, you will have bullets disintegrate in flight.

For light, fragile bullets, I would recommend a 1/12.

I'd pay to see a 55gr. varmint bullet "disintegrate in flight," when shot out of a 1-in-9 barrel. Ain't gonna happen! :cool:

Magnum Wheel Man
May 28, 2009, 10:24 AM
my old Contender barrel was 1 in 12 & was only marginal with 55 grain bullets, it shot 45 & 50 grain bullets really awesome, but only some 55 grainers good

1 in 10" should be plenty fast for 55's nothing wrong with a 1 in 9 if thats more common

Skyyr
May 28, 2009, 10:56 AM
Unless you're using something like really bad PRVI Partizan, there's no such thing as "light, fragile" 55-grain bullet. The XM193 is probably the most-sold civilian round in 5.56 (for all intents and purposes, .223) and it's 55-grain. Until the M855 replaced it, it was the standard 5.56 US military round.

Again, a 1/9" will work best overall for 55-grain bullets. Sure, you might find one brand with a specific powder blend that works better in a 1/12", but unless you plan on firing that single cartridge for the rest of your gun's existence, a 1/9" will suit you best.

In addition, should you to use a heavier round in the future, then you can do so with a 1/9". A 1/12" would already be at its limit with the 55-grain, so you could only shoot lighter (40'ish grain weights) with a 1/12".

Further, you'll find far more 55-65 grain rounds in overall availability compared to the lighter rounds. Again, the 1/9" is just better overall. The 1/12" might be better in some select cases, but, personally, I'd rather have a gun that could handle a wider range of ammo and still perform well compared to one that was limited to 55-grain or less.

Regards...

kraigwy
May 28, 2009, 11:28 AM
To determine the twist required for your 55 grn bullet (or any other bullet)

Divided the Lengh by cal. ( Ln of 55 grn bullet / .22

Divided Specific Gravity by the results of above; (specific gravity for a lead core jackated bullet is 150)

Multiply that result by the cal

For example the twist requred for the hornady 53 grn match 223 (I cant find a 55 grn bullet right off hand)

53 gran 223 Hornady match = .708

.708/.22 = 3.18

150 / 3.18 = 47.17

47.17 X .22 = 10.37

So for this bullet, a one and 10 would work best. Anything between 1 in 9 and 1 in 12 would work.

In Theory. It reality, you can shoot the lighter bullets in faster twist better then you can shoot the slower bullets in slower twist. Within reason. Light jacketed varment bullets (like the 40 grn V-Max) may come apart if pushed too fast down a 1 in 7 twist bullet.

I would recommend that if one was to error, that he error toward the faster twist barrels.

Prof Young
May 28, 2009, 02:56 PM
Dallas Jack, you quired about a one in 12 rate. I have a rem 7 with 1/12 and it shoots 44 gr and 55 gr bullets just fine. I loaded some 68 gr bullets and they tumble. Which gave me a good excuse to buy a new gun with a one in nine. I bought a savage but haven't shot it yet.

Live well, be safe
Prof Young

Dallas Jack
May 28, 2009, 03:19 PM
That agrees with my experience. My 1:12" .223 shoots my 55 gr handload under an inch (sometimes less that 1/2") but shot a 10" group with a 75 gr Hornady Tap round. All rounds keyholed.

My 1:8" AR shoots 75 gr TAP rounds just fine. (between 1.2" and 1.5")

Dallas Jack

M1911
May 28, 2009, 03:31 PM
My Eagle Arms/Armalite Golden Eagle has a 1:8" barrel. It shoots 55gr just fine.

kiwi56
May 28, 2009, 04:04 PM
The only 223 bullets I have actually seen come apart were some early Hornady 40 grainers but these were fired in a 22-250 with a 1:8 twist. it looked like the target had been fired at with a shot gun.

Dood_22
May 28, 2009, 04:12 PM
Unless you're using something like really bad PRVI Partizan, there's no such thing as "light, fragile" 55-grain bullet. The XM193 is probably the most-sold civilian round in 5.56 (for all intents and purposes, .223) and it's 55-grain. Until the M855 replaced it, it was the standard 5.56 US military round.

Neither a Hornady SX nor Sierra Blitz are anything like an M193 FMJ or even a 52gr match bullet for that matter. It has nothing to do with quality, it has to do with designed purpose.

If you want to see a 1/9 smoke a 55gr bullet, IM me and I'll invite you out to my club and you can watch the blue streak as 55gr SXs disintigrate on the way to the target out of a cheap 1/9 barrel.

As an aside, this 1/9 barrel shoots 55gr M193 and 52gr match bullets fine, as well as "really bad" Prvi.


Whether or not a barrel will shoot any given bullet depends upon a few things:

Barrel twist
Barrel/throat condition
Velocity
and lastly and just as importantly,
Bullet construction.

skydiver3346
May 28, 2009, 04:19 PM
I know the 55 grain bullet works fine out of the 1:9 twist barrels. Was just wondering what the heaviest grain 5.56 bullet you can shoot out of a 1:9 twist barrel and still get a good group? Bushmaster AR is the rifle.

kiwi56
May 28, 2009, 04:32 PM
Skydiver, with a 1:9 twist you should be able to shoot up to 75 grainers but sometimes depends on the rifle concerned

Dood_22
May 28, 2009, 04:36 PM
I would never depend upon a 1/9 to shoot it's best with bullets over 70gr.

Skyyr
May 28, 2009, 04:57 PM
@ Dood_22

You mentioned the following:

1) Barrel twist
2) Barrel/throat condition
3) Velocity
4) and lastly and just as importantly, Bullet construction.

Out of those, it's only natural to assume that we're 1) talking about a 1/9" twist (since it was my suggestion to use said 1/9") and 2) that the barrel is in good condition. To assume otherwise would be committing the slippery slope fallacy, because then any other number of factors could be present. That said, #1 and #2 moot points.

It's assumed his gun isn't in bad condition or of cheap rifling/construction; if we did, then why not assume he never cleans it either? Point 2 is assumed and considered non-factor unless specified otherwise.

With 1 and 2 out of the way, that leaves 3 and 4 as semi-valid points. Since we're talking about a 55-grain bullet and a 1/9" barrel, that sort of rules out any excessive velocity, unless you factor in non-standard powder loads. The same applies to #4: unless you're using a poorly constructed round, or a varmint round as I mentioned (hence a super-thin jacket), then he won't have any issues.

That was my original statement, and I'll (politely) state it again: unless you're using cheap or varmint (ultra-lightweight) ammo, a 1/9" is fine.

Thanks and regards...

M1911
May 28, 2009, 07:50 PM
I know the 55 grain bullet works fine out of the 1:9 twist barrels. Was just wondering what the heaviest grain 5.56 bullet you can shoot out of a 1:9 twist barrel and still get a good group?
I don't know about the heaviest. I have shot 69gr Federal Gold Match out of my Colt with a 1:9" barrel with very good results.

blhseawa
May 29, 2009, 12:09 AM
Depends upon:

Bullet weight
Bullet length
Bullet shape
Gilding or Jacket material/coating
Bullet interior
Muzzle Velocity
Powder Pressure Curve
Case overall length
Magazine length
Chamber and Throat length to rifling
Barrel Material
Type of barrel rifling
Length of Barrel

I could give you the complex equations but you get the general idea, and yes I am an engineer.

For the purposes of my answer to your question:

I assume standard AR-15 20 inch chrome lined molybdenum steel (4150) barrel and generally available gilded bullets from Sierra, Hornady, etc.

70 grain bullets is the maximum weight projectile that will be stabilized as predicted by cranking the numbers. As always your mileage may very, depending upon your specifics.

The actual spinning of the bullet acting as mini-gyroscope is what helps improve the bullets trajectory and reduce the small imperfections of a bullet.

To little twist, to short a barrel, to slow the muzzle velocity and the result is a bullet with poor trajectory. (misses the intended target/point of aim).

Generally speaking the heavier the bullet the more spin is required to stabilize the bullet.

In the M4 with it's military configuration 14 ~ 16 inch barrel, the longer and heavier tracer ammo used by the army was not stabilized at the old 1:12 twist rate. Thus the 1:7. 1:9 or 1:8 would have sufficed for the SS109.

Since most people don't shoot a steady diet of tracer ammo, the 1:8 or 1:9 has become very popular among commercial AR-15 makers, IMHO the 1:9 has better range of typical bullet weights that I use then the 1:8. But, that is just me. I'll stop there as I don't want to start another best 223/5.56 cartridge configuration war. Let's just say I'm not a SS109 fan boy and leave it at that!

There are other reasons for 1:9 or 1:8 over 1:7, but if you have a carbine (14 ~16 ) barrel, 1:7 is probably preferable.

As an aside, a lot of National Match or High Power (race) ARs shooting 1000 meter competition have gone to 1:8 to shoot the heavier 75 or 80 grain long range bullets.

I hope this answers your question.

NWCP
May 29, 2009, 02:52 AM
1 in 12 for 55gr .223.

Thermodyne
June 3, 2009, 11:50 AM
I shoot 69gn match ammo very well through a 1-12 twist barrel and also do very will with high speed 40gn loads. The 1-9 twist became popular for the SS109 ammo, which is inherently unstable. They are nose heavy and take a lot of spin to stabilize. A 1-12 will key hole with SS109 and tight group 69gn loads as long as you keep the velocity under control.