Author Topic: What's the story on "Green Tip" Ammo in 5.56  (Read 248619 times)

HAWKFISH

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Re: What's the story on "Green Tip" Ammo in 5.56
« Reply #10 on: October 18, 2008, 10:56:57 AM »
Interesting stuff. So for accuracy of a 16in. AR-15/M4 barrel what would you guys recommend? 62Gr., 64Gr., 69Gr. Hp/ FMJ/SP ? I am curious because I have a friend that says he gets "big groups", from his AR with a 16in. barrel, using only 55gr fmj bullets. Could this Grain weight throw off his groups that much? His gun's barrel is stamped 5.56 too btw. Any thoughts?

Hazcat

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Re: What's the story on "Green Tip" Ammo in 5.56
« Reply #11 on: October 18, 2008, 01:58:45 PM »
What is the twist rate?
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HAWKFISH

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Re: What's the story on "Green Tip" Ammo in 5.56
« Reply #12 on: October 18, 2008, 04:22:08 PM »
What is the twist rate?

Yeah that might help huh?  ::) His is a 1-9 twist, 16in., 5.56mm chrome-lined barrel. He has mostly shot 55Gr. and a box of 60Gr., which seemed a little better. So, perhaps 62Gr.-69Gr. might work better. Thoughts?

MikeBjerum

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Re: What's the story on "Green Tip" Ammo in 5.56
« Reply #13 on: October 18, 2008, 05:05:00 PM »
I'm still learning myself, but from what I've been told the slower twist would be better with lighter bullets.  I have a 1 in 9" and shoot mostly 55 gr right now.  I want to go up to 69 gr or 72 gr for the longer range, but long range shooters are telling me that 69 gr is really pushing the limits of 1 in 9".  They recommend 1 in 8" and to use it with nothing lighter than 55gr.  One "expert" told me a 52 gr through a 1 in 7" won't even hit paper consistantly ... don't know.

My barrel length is 20", most long range guys I talk to are using 20" to 24 inch (most common) with some a couple at 18".

I have shot one box of 69 gr through mine, and it did better at 400 yds than they 55 gr, but it was a matter of a larger group with heavy vs drift on the lighter.  Seems to verify that the heavier bullet needs faster twist to stabilize.  Not sure if barrel length is for twist or full powder burn.

Short version:

I've been told the lighter the bullet the slower the twist, and there is a lot of disagreement of where the need to go from 1 in 9" to 1 in 8" is.
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Big Frank

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Re: What's the story on "Green Tip" Ammo in 5.56
« Reply #14 on: October 18, 2008, 10:00:05 PM »
I think you need to experiment for yourself to find the best bullet weight, and the chart from cactustactical is a good starting point. Something else to consider when getting an M4 contour barrel is that the M203 mounting groove is a weak spot that may cause excessive vibrations between the front sight and muzzle, and may give less accuracy than a "solid" 16" barrel. I haven't seen any real data yet, just hearsay.
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Re: What's the story on "Green Tip" Ammo in 5.56
« Reply #15 on: Today at 12:49:07 PM »

andrews1911

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Re: What's the story on "Green Tip" Ammo in 5.56
« Reply #15 on: September 01, 2013, 02:33:59 PM »
Excellent post Hazcat. The history about the ammo and rifle was good, but I learned a bit about the different types and distinction of the specific rounds. Great article
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les snyder

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Re: What's the story on "Green Tip" Ammo in 5.56
« Reply #16 on: September 01, 2013, 10:04:14 PM »
longer bullets typically have a higher ballistic coefficient... how well the bullet moves through the air without deflection... the heavier bullets will have less wind deflection than lighter bullets... my game gun has a Rock River free floated chrome lined 16" mid, with 1/9 twist... it has an affinity for S&B 55grain M193... and will shoot 5 shot groups into 4" at 400m... hand loaded Sierra 69 grain bullets will shoot the same, but will have 1/2 the wind deflection....

robert69

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Re: What's the story on "Green Tip" Ammo in 5.56
« Reply #17 on: September 02, 2013, 12:31:17 AM »
Regarding rifling twist and over stabilization.
There are a lot of interesting articles on this subject, but unless you are shooting a very light for twist bullet, 40-50 grain in 1-7, 1-9,
you would not see any dramatic problems unless you are shooting over 200 yards.
At those ranges most shooters can't shoot a .223 that well, unless the rifle is set up for it.
For long range (300 yards) squirrel shooting, I shoot a 22-250 at 3600 fps, with a 53 grain HPFB in a heavy 26" barrel. This bullet is a Sierra bench rest bullet. The rifle is a 1-12 twist.  I have shot 45 grain weight bullets, at over 3800 fps, and could not put holes in a target at 100 yards. Why?  We observed that there was a smoke trail to the target, but no hole. You could not do that with a .223, because you could not get enough powder in the case. The assumption is excessive spin for a light bullet caused by very high velocity for that bullet.
Yes, you can over stab a bullet with light bullets and a excessive twist, but it is much more common to go the other way, heavy bullets with slower twist.

 

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