Grain/twist question

[DBLTAP]

I recently purchased a ATI AR chambered in 5.56. It is 1/7 twist and as I was talking with a fellow about ammo. He informed me that it is extremely unsafe to shoot rounds such as 55gr. Due to bullet coming apart. I had never heard of it being unsafe, I have always thought it would possibly affect accuracy but that was about it. Wanting input from some of you if he is correct or not. The use of mine is majority target shooting and occasionally hunting with around 100 yd shots. Thanks in advance

 

[The Pitt]

Ol fellow doesnt know what hes talking about. Lots of misinformation out there. Find the facts on the internet not hearing them from some old Jim Tom. 55gr are good to go.

 

[bohica793]

He is an idiot. My 1/7 puts 5 - 55 grain rounds in one ragged hole at 100. The 55 grain round are supposed to perform better in a 1/8 or 1/9 barrel but they are perfectly safe in a 1/7.

 

[wildrider666]

The fellow can give you his opinion but mine is its BS. Some barrels, twists and bullet weights don't always mix.This issue is not universal to all like ammo, twists and rifles. HOWEVER, Two interrelated factors here. First is barrel quality, an average good barrel with 1/7 twist will shoot 55g to 75g bullets just fine. It is only when shoot very light 35g or heavy 77g+ that you "might" have problems. Twist rates for 5.56/.223 have changed over the years as ammo changes. Unless you have a preference for a specific round that delivers the best accuracy from 1/X twist of XX inch length barrel don't worry about it. I don't shoot ultra fast very light rounds, no need for the speed. Buy a few boxes in different weights. Do the normal reliability and accuracy checks then buy bulk of the best load. Good luck.

 

[Little Jack]

Plus 1 with wildrider. 55gr out of a 1/7/sound be fine. By no means "unsafe". Keep in mind that barrels will prefer certain bullets, regardless of twist/the etc.

 

[DBLTAP]

Soon as he said it I knew it sounded off, and I couldn't find anything to back it on the net. I appreciate the replies just wanted clarification from yall on it.

 

[SAWMAN]

I have shot 35gr .224" bullets out of a 1:7 twist 24" bbl at max speed. IIRC it was about 3600fps.(rotational velocity >370,000RPM) I have also shot 125gr NosBalTips out of my .30-378Wby Mag at >4200fps with it's 1:10 twist bbl.(rotational velocity >302,000RPM

I have never witnessed a bullet coming apart in flight but have seen this when they hit one blade of grass. --- SAWMAN

 

[bigbulls]

Bullets can absolutely come apart in mid flight if they are spinning fast enough for a given bullet diameter, the jackets are thin enough and the bullets heat up enough.
The larger the bullet diameter is the higher the centripetal force will be on the bullet. A .224" bullet turning 300K rpm will not exert as much force on the bullets jacket as a .308" bullet turning 300K RPM.

Having said this, you would have to be shooting very light weight, thin jacketed varmint bullets in order to get them to come apart out of a .223.

For example, if you were firing a 35 grain Vmax at max .223 velocity (about 3900 fps) out of a 24 inch barrel then the bullet would be spinning over 400,000 rpm's.
That same bullet out of a 16" barrel would be turning about 360,000 RPM's. This might be getting close but probably wouldn't come apart.
A 55 grain bullet out of a 16" barrel will be turning about 295,000 RPM's and would be a long way off from coming apart in mid flight.

However, if one did come apart.... as far as it being unsafe, it isn't. The bullet will not come apart inside the barrel. It usually does so well down range of the muzzle.

 

[Crazydoc68]

1/7 twist are made for the longer bullets. That said the military uses that twist rate so we can use the 77gr OTM out of shorter barrels. 55gr, like many others have said will be fine.

Just like how many times ive heard "a 50calBMG only has to come within 4 feet of someone amd will rip their arm off". Ive shot the 50cal many times and in combat and ill tell you it does NOT have that effect....lol

Doc

 

[donr101395]

The only bullets I've seen adversely affected by a 1/7 twist rate were very thin jacketed light weight varmint bullets. Years ago I had some 40gr that would spin the jacket off and disintegrate 10 yards after leaving the barrel. It wasn't dangerous, just annoying.

 

[bluedsteel]

He needs to contact the US military since they have been known to use M193 (55gr) in M16s and M4s which have the 1:7 twist.

Probably been trying to find out what's wrong for decades. :lol:

 

[SAWMAN]

As much as I can remember ...... for years the heaviest bullet shot in the 223/5.56 guns was the 55gr. When the 62gr bullets came out the twist rates went from 9 down to 8 and 7 for some odd reason. A 9 will easily handle a 62gr but not a 12 twist.

I remember one of the first Mini-14's that I had was a 1:10 twist. People thought that it would spin the Hornady 50gr SX bullets apart. I could never get one to come apart at 3150 or so. Later when I got my 220Swift I used to shoot them at 3850 out of the 1:14 twist bbl with no problems if you did not hit grass on the way to the woodchuck from the prone position. --- SAWMAN

 

[Rapier]

Sounds like the origns of this is a LGS cowboy that hangs out at the LGS to try and impress other customers with their newly found "knowledge." If you have average hearing you will hear these conversations at just about every LGS in the area.
Ed

 

[SAWMAN]

You above is absolutely correct. But to me,the winner is ---> Academy. --- SAWMAN

 

[donr101395]

As much as I can remember ...... for years the heaviest bullet shot in the 223/5.56 guns was the 55gr. When the 62gr bullets came out the twist rates went from 9 down to 8 and 7 for some odd reason. A 9 will easily handle a 62gr but not a 12 twist.

I remember one of the first Mini-14's that I had was a 1:10 twist. People thought that it would spin the Hornady 50gr SX bullets apart. I could never get one to come apart at 3150 or so. Later when I got my 220Swift I used to shoot them at 3850 out of the 1:14 twist bbl with no problems if you did not hit grass on the way to the woodchuck from the prone position. --- SAWMAN

It went down to a 1/7 to stabilize the longer M856 tracer rounds which are longer and heavier than the original M196 tracer

 

[wildrider666]

Just like how many times ive heard "a 50calBMG only has to come within 4 feet of someone amd will rip their arm off". Ive shot the 50cal many times and in combat and ill tell you it does NOT have that effect....lol
Doc

I have seen "missed" M2 50BMG rounds and what they hit create shrapnel and pink mist. I guess "Close enough for Government work." Isn't always a bad thing. Lol