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Started By
Message
re: what are the superior "brands" of the AR15?
Posted on 1/26/15 at 7:30 am to chrisman17
Posted on 1/26/15 at 7:30 am to chrisman17
Not mad but it gets tiring to see bullshite spread around by those that should know better.
0
Posted on 1/26/15 at 9:33 am to Clames
So the military needs a 7 twist barrel to stabilize a 64gr bullet? Why would I want a 9 twist again in a 3grand rifle? I get it for a $500 generic m4, but not a high end gun with $1000+ barrel on it.
Posted on 1/26/15 at 9:45 am to kengel2
Do you understand that it isn't just weight but also composition and shape that determines the proper rate of twist? Go look at M856 bullet compared to a M855 and notice how much longer that tracer bullet is. That might clue you in to why that 7 twist was chosen. If a 9 twist barrel shot better than a 7 twist barrel in a $3k rifle why the frick would I care that it isn't a 7 twist? Pretty sure a custom Lothar 1/9 has more accuracy/precision potential than FNH hammer forged 1/7 twist over the same bullet weights. Smart money is looking at the total system and not getting hung up on the twist rate.
This post was edited on 1/26/15 at 9:53 am
Posted on 1/26/15 at 9:56 am to Clames
I understand more than most.
You don't care, it's obvious.
But what good is a 3k rifle that may or may not shoot commercially available ammo? Especially an AR. Hey buy this buy 3k AR and you may or may not be able to shoot 77gr ammo because we were to lazy to put an 7 or 8 twist barrel on it. That 69,75, or 77 grain ammo you bought might keyhole but it's cool.
You don't care, it's obvious.
But what good is a 3k rifle that may or may not shoot commercially available ammo? Especially an AR. Hey buy this buy 3k AR and you may or may not be able to shoot 77gr ammo because we were to lazy to put an 7 or 8 twist barrel on it. That 69,75, or 77 grain ammo you bought might keyhole but it's cool.
Posted on 1/26/15 at 10:23 am to kengel2
I do care and I know a lot more than you about this topic. If it wasn't for FN's development of what we call the M249 SAW, the NATO push for longer range performance than 55gr M193 could deliver, and the USMC requirements all coming together, the 1/9 twist would have been selected as it is the optimum twist to stabilize M855 (SS109) ball ammo. 1/7 twist was selected based on the tracer ammo design and the desire to capture some of the terminal wounding performance lost from the 55gr M193 ammo since NATO refused to standardize on the M193. You are operating on ignorance (seems to be a common theme around here), 1/9 twist will stabilize 75gr bullets just fine and even the shorter 77gr bullets (Nosler vs SMK) depending on how it's loaded. Too lazy? Why don't you stop being lazy and start doing some research... 
Posted on 1/26/15 at 10:43 am to Clames
After reading a few barrel manufacturer's suggestions and about 10 different websites on the topic, they all agree that 1:7 is best if you are shooting on the heavier side mainly and will still work perfectly fine on the lighter stuff, but 1:8 is the best for both lighter and heavier loads. They said 1:9 will stabilize the heavier stuff, but not as well as 1:7 or 1:8, and do not recommend it for anything above 62gr.
I have no skin in the game, but that's what reputable people say
Eta: All things being equal (non-tracer or specialized rounds), wouldn't weight be a direct reflection of length since the OD has to be the same?
I have no skin in the game, but that's what reputable people say
Eta: All things being equal (non-tracer or specialized rounds), wouldn't weight be a direct reflection of length since the OD has to be the same?
This post was edited on 1/26/15 at 10:49 am
Posted on 1/26/15 at 10:46 am to Hammertime
I saw a show on outdoor channel recently that did tests with different weights and different twists. 3 different rates. I was only halfway paying attention since I'll never own a 5.56 or .223, but the slowest twist of the three was basically ruled out.
Posted on 1/26/15 at 10:50 am to AlxTgr
So they basically made the "slow" kid go to another school? Typical gun guy reaction
Posted on 1/26/15 at 6:03 pm to Clames
quote:
You are operating on ignorance (seems to be a common theme around here)
Damn, you really think alot of yourself dont you.
quote:
Too lazy? Why don't you stop being lazy and start doing some research...
Sorry, I was at work and trying to use my memory. Got home and pulled a book off the shelf. Pretty cool book about Ballistics by Bryan Litz (cheif ballistician at Berger bullets). I think you would agree that he is a SME. Everything depends on muzzle velocity and atmospheric conditions. We'll just use our weather down here. Im looking at stability factors of bullets and it pretty amazing. Remember how I said that a 9 twist may stabilize the heavies, but a faster twist would be better? We'll use the formula in the link below, Im sure its the same used in the book since its the same person doing all the testing.
Berger Bullets
Assume a stability factor of 1.5(taken from the link) indicates good stability. This doesnt necessarily mean it wont work, just that its not ideal.
9 twist barrels:
62gr lake city 1.07
77gr lapua 1.04
69gr Lapua 1.39
75gr Hornady bthp 1.21
68gr Hornady bthp 1.08
77gr Nosler CC 1.28 (68gr wasnt tested dont know why)
77gr Sierra smk 1.2
69gr Sierra smk 1.43
55gr Sierra FMJ 1.91
8 twist
62gr lake city 1.35
77gr lapua 1.32
69gr Lapua 1.76
75gr Hornady bthp 1.54
68gr Hornady bthp 1.37
77gr Nosler CC 1.61 (68gr wasnt tested dont know why)
77gr Sierra smk 1.52
69gr Sierra smk 1.81
55gr Sierra FMJ 2.42
7 twist
62gr lake city 1.77
77gr lapua 1.72
69gr Lapua 2.29
75gr Hornady bthp 2.01
68gr Hornady bthp 1.79
77gr Nosler CC 2.11 (68gr wasnt tested dont know why)
77gr Sierra smk 1.98
69gr Sierra smk 2.37
55gr Sierra FMJ 3.16
So like I said earlier, a 9 twist may stabilize the heavy bullets sometimes. Its not always a given and can change with the weather. Its dumb for a manufacturer selling a $3000 rifle to use an outdated twist rate that isnt sufficient for modern bullets.
There is my research, it is certainly more credible than anything you have brought.
Posted on 1/26/15 at 6:06 pm to kengel2
Great post.
Posted on 1/26/15 at 8:49 pm to chrisman17
I have a RRA 6.8 - One of the best 6.8 platforms on the market in my budget - more accurate than me - and I am fairly confident the SPC II is mil-spec
Posted on 1/26/15 at 9:13 pm to kengel2
All right. Dumb question time. Some of us are just now learning. Explain twists for a beginner. Thanks.
Posted on 1/26/15 at 9:23 pm to kengel2
quote:
Damn, you really think alot of yourself dont you.
When you put you ignorance on display it doesn't take much to get called out for it.
quote:
I think you would agree that he is a SME.
He is one SME, I don't base my understanding on ONE SME though, I use dozens.
quote:
Everything depends on muzzle velocity and atmospheric conditions.
Oh look, earlier you were only focused on bullet weight to the exclusion of other bullet parameters. Now you think it's only about MV and atmosphere. Good job, now you have half a chance of understanding why the Army changed the M16 from a 1:14 to a 1:12 twist early on.
quote:
Remember how I said that a 9 twist may stabilize the heavies, but a faster twist would be better?
You didn't say a damned thing like this, you simply stated 1:9 twist was "scrappy" at first then attempted to go on about how it may or may not stabilize a heavier weight bullet.
I am very much aware of that (and many, many other) online ballistic calculator. I also understand the simplified mathematics behind them and that they are only to be used as very, very rough estimate for selecting a barrel given a certain cartridge. Per you own information, you conclude the 62gr M855 is only marginally stabilized by a 1:9 twist barrel. This is completely false as the Army (firing thousands of SS109 through various barrels using radar-based data collecting equipment) found the 1:9 twist to be the optimum rate for SS109 (SS109/M855 because this was before the standardization under NATO specs). This just highlights the difference between you using only a single reference and a shallow understanding of the subject and my considerably deeper understanding of this topic. Notice that calculator does not consider the length of the rifle barrel which, in function with MV, does impact and promote stability with respect to initial yaw and resulting precession of the bullet as it exits the muzzle. Very important detail in understanding why a given manufacturer might choose a 1:9 twist over a faster rate.
Posted on 1/26/15 at 9:52 pm to prplhze2000
H&K
LWRCI
LWRCI
Posted on 1/26/15 at 10:06 pm to BamaScoop
Since obviously there is alot of kNowledge in this thread can someone tell me if a Double Star .308 is a good gun for the money. Looking to shoot deer and hogs and want an ar. Buddy recommended it to me. Please advise.
This post was edited on 1/26/15 at 10:07 pm
Posted on 1/26/15 at 11:12 pm to prplhze2000
LWRC
/thread
/thread
Posted on 1/26/15 at 11:20 pm to goatman1419
Get an M1A.
Posted on 1/27/15 at 9:10 am to dnm3305
damn there is some knowledge being dropped in here... All I know is pull the trigger and go PEW PEW
Posted on 1/27/15 at 10:02 am to chesty
Wait until we start the mindnumbing "which forged lower is better" discussion.
Posted on 1/27/15 at 10:06 am to Pettifogger
These threads deliver.
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