Question on twist in the Barrel

Galliente · #1 10-08-08, 14:04

Ok ...I am betting this has been asked a half a million times by now...But I am new to the site and I am also new to the Customizing of the Black Rifles......Ok dont hurt me to much on the replies...LOL......OK whats the difference in a 1:7 twist in a 16 " Barrel compared to a 1:9 twist?...Is there a major change in accuracy,range or velocity of the round?....The caliber would be in a .223 ...Thanks for the info

JBnTX · #2 10-08-08, 14:13

Quote:

Originally Posted by Galliente

...Is there a major change in accuracy,range or velocity of the round?....The caliber would be in a .223 ...Thanks for the info

A lot depends on the bullet weight you intend on using.

All other things being equal, heavier bullets will require a faster twist to
stabilize them.

Check out this page: Scroll down. Some of it's messed up but
what your looking for is there.

http://www.ammo-oracle.com/body.htm

markm · #3 10-08-08, 14:17

Quote:

Originally Posted by JBnTX

A lot depends on the bullet weight you intend on using.

All other things being equal, heavier bullets will require a faster twist to
stabilize them.

It's actually LONGER bullets that require a faster (1/7) twist rate. For example, the 50 grain Fed NT frangible is relatively light. But the bullet is very long. Thus you need a 1/7 for any decent level of stabilization. 1/9 twist shooters have reported bad keyholing.

JBnTX · #4 10-08-08, 14:20

That's right.

I meant longer bullets.

Galliente · #5 10-08-08, 14:47

Thanks for the replies...That helps a lot.....So
For my brains sake...Since I am not to good at understanding tech talk....ya'll are saying that ....say for instance a nato 5.56 has just a little bit longer bullet ...when fired the bullet is more stable out of a 1:7 twist barrel....and on average the regular commercial bullets are just a bit shorter...and have better flight caracteristics out of a 1:9 twist....Crap I have to write more later ...Ill get back to this in a few hours ...I have to go Dive....Ill be back..

markm · #6 10-08-08, 14:57

1/9 works fine for Nato ammo (M855 green tip) and 55 grain ball ammo. The reason the military used 1/7 is because the M856 Tracer rounds is VERY long.

If you plan to shoot any bullets heavier than 69 grain, you might want a 1/7 twist rate.

1/9 twist is all I need, but some of my barrels are 1/7 just because that's the current fad.

Olav · #7 10-08-08, 23:20

Quote:

Originally Posted by demigod

1/9 works fine for Nato ammo (M855 green tip) and 55 grain ball ammo. The reason the military used 1/7 is because the M856 Tracer rounds is VERY long.

If you plan to shoot any bullets heavier than 69 grain, you might want a 1/7 twist rate.

1/9 twist is all I need, but some of my barrels are 1/7 just because that's the current fad.

I was doing a little research on this and there is an alternative view as to the origin of the 1/7 twist.

Here's an excerpt:

Quote:

"In testing for the M-1A2, the twist rate of 1/7 was settled on. Why? I've heard two reasons: one, that it was needed to stabilize tracer bullets. As we adopted the M-856 tracer well after settling on the 1/7 barrel, I doubt it. The other was that preliminary testing done in Europe for the SS-109 bullet used barrels with a twist as fast as 1/7. Since it worked with all lesser weights(the SS-109 tests went well beyond the 62 grains of the SS-109 and M-855, up to 100 grains) why not use the fastest twist with tested results?" Page 50

The Gun Digest Book of the AR-15 by by Patrick Sweeney

What do you think?

markm · #8 10-09-08, 09:23

Yeah. I don't know which of the proposed reasons is 100% correct. But I do know the 1/9 doesn't stabilize the M856 very well.

Galliente · #9 10-09-08, 23:19

Well that information has been very helpful to me...I am going to go with a 1:9 twist since a 55 grain bullet seems to be more common where I am living...I am glad to have everyone on this site to ask questions...Thanks everyone...

Robb Jensen · #10 10-10-08, 08:56

1x7 twist was used because it worked in the M249 for stabilizing the very long M856 tracer so why reinvent the wheel?

Don't believe it?

Just ask member coldblue (aka LtCol David Lutz USMCR).

Lt Col Lutz and Maj Jack Muth USMCR were both my dads (GySgt RJ Jensen USMCR) boss' at Quantico Firepower Division which is where the USMC spec'd out what became the M16A2. My dad didn't get stationed there until 1986 (three years after the M16A2 was adopted by the USMC) but he worked on the XM4 project as well as the Mk19Mod3 and many other weapon systems.

Failure2Stop · #11 10-10-08, 09:29

Quote:

Originally Posted by Galliente

Well that information has been very helpful to me...I am going to go with a 1:9 twist since a 55 grain bullet seems to be more common where I am living...I am glad to have everyone on this site to ask questions...Thanks everyone...

Using a 1:9 limits you to 69 grain (roughly, depending on barrel and ammo) and under weight bullets. 1:7 still works for the lightweight bullets, but stretches your upper limit considerably.

Why impose limits on yourself? It's not like you are paying a premium for 1:7 barrels.

LOKNLOD · #12 10-10-08, 09:58

Quote:

Originally Posted by Olav

The Gun Digest Book of the AR-15 by by Patrick Sweeney

What do you think?

This is a bit of a hijack but is that an AR-10 on the cover of the AR-15 book?

On-topic, I agree with F2S, no reason not to get a 1:7 if they're available. I wouldn't sell my 1:9 to get a 1:7 just for the sake of having it, but there's no real drawback to the 1:7.

Only exception I can think of might be if I planned on building a long barrel varminter firing 40-45 gr. rounds primarily. But that's a whoooooole different discussion.

Olav · #13 10-10-08, 10:54

Quote:

Originally Posted by gotm4

1x7 twist was used because it worked in the M249 for stabilizing the very long M856 tracer so why reinvent the wheel?

The 1/7 twist was adopted in the 60s while the M249 was adopted in 1982 replacing the bipod-mounted M16A1 automatic rifle and the M60 GPMGs. (NATO still used the GPMG and the FN C2, which I used)

So, the twist was carried over to the new weapons system because it can stabilize the M856, adopted in 1982, which weighs in at 64 grains (L110 projectile) while the M855 ball cartridge uses the Belgian SS109 bullet which weighs 62 grains.

Is that what you mean?

Olav · #14 10-10-08, 11:00

Quote:

Originally Posted by LOKNLOD

This is a bit of a hijack but is that an AR-10 on the cover of the AR-15 book?

Volume II looks good...

Robb Jensen · #15 10-10-08, 11:50

Quote:

Originally Posted by Olav

The 1/7 twist was adopted in the 60s while the M249 was adopted in 1982 replacing the bipod-mounted M16A1 automatic rifle and the M60 GPMGs. (NATO still used the GPMG and the FN C2, which I used)

So, the twist was carried over to the new weapons system because it can stabilize the M856, adopted in 1982, which weighs in at 64 grains (L110 projectile) while the M855 ball cartridge uses the Belgian SS109 bullet which weighs 62 grains.

Is that what you mean?

Kinda. The M249 Minimi was used by the US Marines during the development of the M16A2. The USMC went with 1x7 because they new it worked with the M249 using the M855 and M856 tracer rounds. No need to develop a new twist for the new M16A2........no need to reinvent a new twist just for the M855 since 1x7 worked sure 1x9 would work too, but they new for sure the 1x7 would work.

warpigM-4 · #16 10-10-08, 12:09

when i got to FT Knox and was issued my M4 I thought it would have a 1x9 twist like the old colt sporter I had.But it was the 1x7 after shooting and training with it .And learning why it was 1x7 (for heavy bullets and tracers) I thought they know something so I went with the 1x7

.The 1x9 I had years ago keyholed like crazy but I really didn't know what was causing it.(I was a AK guy) But now I know and knowing is half the battle

damn I just quoted GI JOE