My girlfriend's dad gave her a rifle (http://www.thehighroad.org/showpost.php?p=2435404&postcount=79) for last Christmas (I should have such parents – then again I'm not from Texas and her family is; go figure.) And she loves to shoot but isn't completely familiar with all the basics and various trivia and ephemera that tends to build up in the brain of the dedicated firearms enthusiast.
But she cornered me with a question regarding barrel twist rate vs. bullet weight the other day that I couldn't answer. Her rifle is a new Remington XR-100 in .223 and we were plinking away the other day and she wanted to know why the rifle had a 1:12 twist rate.
After I explained how faster twist rates lend themselves to better accuracy with heavier rounds and slower twists work better with lighter rounds, she asked wouldn't a heavier round be more accurate at longer distance (and since this rifle is advertised as a entry level bench rest rifle) why doesn't it have a faster twist.
Guys, she stumped me. Why exactly is 1:12 so common for .223 long guns? I know a heavier round will buck the wind better at longer distances so why not a faster twist straight from the factory?
Help me out here; I have her convinced that John Browning, Gaston Glock and Eugene Stoner and I hang out all the time talking guns and that I personally am the end all and be all of firearms knowledge.
I'd hate to break the truth to her!
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May 10, 2006, 04:04 PM
As far as I know, 1:12 was the twist rate for the first M16s used back during the Vietnam "conflict." That was okay for 55gr ammo, but when they changed over to 62gr ammo they needed a faster twist barrel and the newer M16s (as well as most civilan AR-15s) came with 1:9 barrels.
The newest M16/M4 ammo is even heavier -- 72gr or 77gr, and that ammo needs a 1:7 barrel for effective stabilization.
I know less than zero about any other rifles that shoot .223 ammo, but based on what works in the AR-15/M16 world, I wonder where you got the information that 1:12 is common for .223 rifles.
May 10, 2006, 04:23 PM
The faster twist rate also increases the spin - rpm - of the bullets. Lighter bullets have a tendency to also come apart at the higher rpm of a 1 in 7" or 1 in 9" twist. Most people using bolt action 223s are not using the 70-80gr bullets. Most varmint bullets are in the 50-55 gr range. So to keep accuracy on a 50-55 gr bullet, you can't spin it so fast that it tries to come apart.
May 10, 2006, 04:56 PM
I wonder where you got the information that 1:12 is common for .223 rifles
I'm talking about bolt guns; the majority of them all seem to be 1:12 which is great for relatively light rounds, but if you've got a 24" - 26" barrel and you're putting a scope on it, then the logic is you maybe be taking longer range shots. So it would seem that the heavier rounds would be more desirable - therefore a faster twist is more desirable.
May 10, 2006, 05:08 PM
bolt gun + 223 = varminter
223 + light bullets = explosions
red mist = fun
223 + heavy bullets = no explosion = not as much fun.
bench guns have ppc or br in their name.
May 10, 2006, 05:17 PM
After all the "best gun for my girlfriend" threads I was afraid this was going to be a "best twist rate for my girlfriend" question!:uhoh:
Anyway the 1-12 twist was used when the heaviest common bullet for a 223 was 55 grains. Experimentation showed that to work great. When the AR became used more often for highpower, heavier bullets were found to be an advantage at the longer ranges they shoot. Thus faster twists became the norm.
May 10, 2006, 05:28 PM
Early .22 centerfires like .22 Hornet had 16" twists like .22 LR and shot 40-45 grain bullets. (Length is what determines twist requirements, a boattail spitzer will be lighter than a flatbase roundnose but if the lengths are the same, the twist needed is the same.)
For many years the larger .224 centerfires were standardized on 14" twists for 50-55 grain bullets. They will stabilize somewhat heavier ones, my .22-250 does very well with 60 grain flatbase bullets.
The VERY first M16 .223s had 14" twist like the parent .222 and .222 Magnum but the Army found that it would not stabilize the relatively long M193 55 gr FMJ boattails in the cold dense air of arctic weather testing so they went to a 12" twist which has remained common in many varmint model .223s.
Service rifle target shooters soon went to a 9" twist for 69 grain boattail bullets at up to 600 yards.
The Army wanted more range and penetration so they went to the SS109 62 grain half-steel core bullet. It would be stable from a 9" twist but the matching SS110 tracer is a very long bullet and needs a 7" twist so that is what they adopted.
The target shooters moved on to heavier bullets for less wind deflection at longer ranges and now use 7, 7.5, 7.7, and 8" twists for 75, 77, and 80 grain bullets. You can go farther, I have a 6.5" twist .223 for shooting 90 grain bullets. It is kind of a developmental thing but is interesting to work with.
Benchrest shooters stayed with 14" for 52 grain bullets at 100-200 yards because they knew that the very best accuracy is with enough, but no more twist than needed for the bullet length. Bullseye target shooters use heavier bullets out of faster twists for reduced wind deflection at 200, 300, 600 yards, not for absolute best grouping ability in calm air.
Most .223 sporters have 12" twists because the makers know that cheapskate shooters will insist on plinking with real or imitation military surplus M193 ammo that needs that rate of twist. That is enough because varmint hunters use generally light bullets at high velocity to do horrible things to cute fuzzy groundhogs and prairie dogs.
May 10, 2006, 06:09 PM
After all the "best gun for my girlfriend"
Nah, she already has her own; the Remington XR-100 and she just picked up a Sig 228.
Mister Watson, you have my extreme thanks. That was exactly what I was looking for. Outstanding.
And instead of boring my girl with all that wonderful data (I can see her eyes glazing over already) I'll simply tell her something she can relate to quite easily:
cheapskate shooters will insist on... military surplus and light bullets at high velocity to do horrible things to cute fuzzy groundhogs and prairie dogs
She's got a bloodthirsty streak in her and likes the idea of varmint shooting and the whole 'red mist' thing. Gotta love her.
May 10, 2006, 08:43 PM
Yup. Watson nailed it. I will just add my personal experience that Winchester's 45 gr. high velocity .223 varmit bullets WILL tear apart in mid air about 30% of the time when fired from a rifle with a twist of 1:9 or faster.
But they work great in a 1:12 rifle, and in mine, they shoot MOA or better out to 200 yards.