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Twist rate, bullet weight, and a question
Kevin_L
Member Posts: 2,011 ✭✭✭✭
I see the most common 223 Remington ammo is 55grains. I also see that most AR-15s have a twist rate of 1:7.
Most calculations and 'experts' say a 1:7 twist works best with heavier bullets and my experience backs that up. My 75grain reloads are way more accurate than the 55grain in my 1:7 AR-15 barrel.
So, why is the majority of the ammo substandard for accuracy in the most popular rifle?
🇺🇲 "The tree of liberty must be refreshed from time to time with the blood of patriots and tyrants." - Thomas Jefferson 🇺🇲
Comments
Good question
I have wondered the same thing
But then I am I just a nobody
55 gn bullets will shoot OK in a 1/7 barrel, 75 gn bullets will not shoot at all in a 1/12 barrel. if you want top accuracy buy 75 gn match ammo.
I have a 1:8 twist barrel
I heard once or read some where that when useing 55gr. bullets in a 1:7 twist the bullet tends to yaw around the center axis and is not as accurate. Now if it’s a thin jacketed bullet in 55gr I’ve heard of bullets fragmenting in flight, a 1:7 would give it more RPM. I had an AR once ( older one) but had the 1:12 twist and I only shot 55gr bullets through it . I’ve got 223 now in bolt action with 1:12 twist, does great with 50 and 55gr bullets.
Here is a formula for finding RPM of a projectile.
Divide 12 by the twist rate—-multiply that number by the velocity—— multiply that number by 60. This equals the RPM.
12/8=1.5 X3240=4860 X 60 = 291,600 RPM
I had no idea. Thanks @waltermoe
Over-stabilization is not necessarily good with lighter bullets....…and sometimes destructive.
A visit to the JBM Ballistics website can be enlightening.
Years ago...…I had fun/frustration with the Berger 37VLD, in my Sako 17PPC. 🤯🤠
BTW....…yote was taken with a L.R.B. 32VLD solid.
"So, why is the majority of the ammo substandard for accuracy in the most popular rifle?"
Sub-standard??? I've not seen a problem shooting 50-55 in a 1/7 twist. For most users, shooting 60-62 grain in a 1/9 twist will not be a big problem. Over 62 will likely be less accurate in 1/9 twist.
What I did find is that 40 grain in a 1/7 may not be the best combination—some barrels will work and some won't. 40 grains in a 1-10 is a good combination.
That's right! SUBSTANDARD ACCURACY!!!! I said it! 😁
I mind that a 55grain bullet in a 1:7 twist 18" barrel is less accurate than a 75grain bullet in the same barrel. So I reload at 75grains these days.
But it's not really about the accuracy. The question is why is 55grain so prevalent when pretty much every piece of data you can find says the 1:7 twist in an AR is best suited to bullets significantly heavier than that.
🇺🇲 "The tree of liberty must be refreshed from time to time with the blood of patriots and tyrants." - Thomas Jefferson 🇺🇲
I would assume that the military takes precedence on heavier bullet loaded ammunition. To ammunition manufactures it would I suppose comes down to keeping something on the market for civilian use. The 5.56 mm was derived from the .222 Remington and the .222 Remington magnum, both developed as varmint cartridges at the time, and were not designed to shoot heavy bullets.
It would be interesting to know what the ratio is, bolt action rifles vs AR platform rifles that are manufactured.
There's a lot going on barrel length, barrel twist and bullet weight.
"That's right! SUBSTANDARD ACCURACY!!!! I said it!"
In WHAT CONTEXT? I have a .223 hunting rifle with 24" barrel that produces 'patterns' rather than 'groups' with any bullet weight over 55-60 grains. It's a great varmint rifle @300 yards with 40 grain V-Max.
There's dedicated light bullet twist rates and there's heavy bullet twist rates. You wouldn't choose a little 4 cylinder engine for a trailer toter nor a big V-8 for an economy special.
In the context of 55 grain vs 75 grain at 100 yards with my rifle. 55 was comparatively all over the place, 75 is much significantly tighter.
But the question was: if 1:7 twist rates (the most common for AR-15s) are indeed best with heavier bullets (75grain and up), why is the predominant 223 Rem bullet weight 55grain?
I find so much BS related to shooting, so much that is just folklore and "my brother's best friend's uncle's son had that happen…" that I've started to wonder if twist rate and bullet weight are also part of that fertilizer blend.
🇺🇲 "The tree of liberty must be refreshed from time to time with the blood of patriots and tyrants." - Thomas Jefferson 🇺🇲
My Rock River Arms varmint with a 1:8 twist gives great accuracy with 50 to 55 grain bullets. The load I settled on uses the 52gr Sierra HPBT match. The day I sighted it in Judy took a few shots from the bench at 50 yards, for whatever reason she didn't want to shoot at my 100yd targets. After 2 one hole five shot groups, one measuring .35 and the other .38, she smiled and said "not bad". Bob
"55 was comparatively all over the place, 75 is much significantly tighter."
What type of 55 grain? Multiple types/brands of 55 grain or just a random pick?
What type of 75 grain ammo? Most 75 grain .223 ammo is a higher quality than generic 55 grain.
I turned a 4MOA AR into a 1 MOA AR by switching from el-cheapo generic FMJ to a better quality 55 grain ammo choice. I maintain a variety of ammo in 40-68 grains to accommodate the preferences of different barrels.
"why is the predominant 223 Rem bullet weight 55grain?"
1: That was the original loading for the .223.
2: Since most users are just 'fun blasters', accuracy may not be important.
3: In most cases, .223 55 grain is cheaper for those above to throw against the berm.
Good questions.
55 grain: PMC factory ammo (fmj). Easy to find just about anywhere. I grabbed a bunch a long time back, before I started reloading the 223.75 grain: Hornady BHTP bullet, 22grains H335. Loaded into the spent PMC brass.I didn't know that 55gr was the original load for the 223. I learn something new every day. :)
The other two items I figured would be reasons for the abundance of 55gr that I see. Especially when you notice the guys next to you doing multiple mag dumps to see who's fastest. Accuracy be damned and the rounds better be cheap!
I don't have any 55gr bullets for reloading but you've definitely got me interested in giving them a try. Sure appreciate the input, @Mobuck. I may grab some 55gr bullets tonight and see how they do this weekend. 👍️
🇺🇲 "The tree of liberty must be refreshed from time to time with the blood of patriots and tyrants." - Thomas Jefferson 🇺🇲