Confused about Twist 1/7 or 1/9

[Sig357]

I will soon start to put together my first Ca. legal AR. I am searching for info on purchasing the upper, and I am leaning towards CMMG, or maybe Del-ton or Stag. I hear CMMG is better but they don't offer 1/9 twist at their website. And I understand that 1/7 twist is better if you will be shooting ammo that is 70 or 75 grain and really long distances. Typically the ammo found at stores is 55 to 65 grain will it be okay to shoot this 55 grain ammo out of a 1/7 twist barrel?

I have also decided to go with the bullet button so I can have all the evil features
I want. The hell with the DOJ, seems like the law is on our side on this one.


Thanks

[tenpercentfirearms]

The newbie thread has a link to twist rate discussions.

http://www.calguns.net/calgunforum/showthread.php?t=56818&highlight=twist+rate

[Sig357]

The newbie thread has a link to twist rate discussions.

http://www.calguns.net/calgunforum/s...ght=twist+rate

Thanks I had already read that thread. Unfortunately there are too many opinions on what twist rate is best on certain loads. I will read it again later and see if I can come up with a decision.
.
Thanks for the help.

[Jicko]

Sig357, please help me to make that "Newbie tips" better, what are you still confused in terms of 1/7 and 1/9?

I quoted this thread in the "tips" posting, and it does explain the capability of both 1/7 and 1/9.

Theoretically,
1x7 shoots anything from 50gr - 77gr and to even heavier ones like 80gr and 90gr(but 80/90 are not magazineable)
1x9 shoots anything from 40gr - 69gr

So, for the most popular XM193, 55gr or XM855, 62gr.... BOTH will shoot fine.... the DIFFERENCES would be the low and high end.....

varmint specific bullets 40-50gr will be served by 1x9 and not 1x7... (by the way, you can shoot varmint with 50gr or 55gr bullets )

recently developed(more like adopted), military performance rounds, 75-77gr will be served by 1x7 and not 1x9... ie. these longer range, premium rounds, cannot be stablized with a 1x9 barrel...

and the military had switched over to 1x7 barrels for a long time now.... and basically those heavier bullets (75-77gr), are used to extend the performance of the M16 platform....

so, imho, 1x7 is the way to go

hope this helps.

[Sig357]

Sig357, please help me to make that "Newbie tips" better, what are you still confused in terms of 1/7 and 1/9?

I quoted this thread in the "tips" posting, and it does explain the capability of both 1/7 and 1/9.

Theoretically,
1x7 shoots anything from 50gr - 77gr and to even heavier ones like 80gr and 90gr(but 80/90 are not magazineable)
1x9 shoots anything from 40gr - 69gr

So, for the most popular XM193, 55gr or XM855, 62gr.... BOTH will shoot fine.... the DIFFERENCES would be the low and high end.....

varmint specific bullets 40-50gr will be served by 1x9 and not 1x7... (by the way, no one limit you to shoot varmint with 50gr or 55gr bullets )

recently developed(more like adopted), military performance rounds, 75-77gr will be served by 1x7 and not 1x9... ie. these longer range, premium rounds, cannot be stablized with a 1x9 barrel...

and the military had switched over to 1x7 barrels for a long time now.... and basically those heavier bullets (75-77gr), are used to extend the performance of the M16 platform....

so, imho, 1x7 is the way to go

hope this helps.

Thanks JickoRicko

I guess I was unsure about shooting 55grain out of a barrel with 1/7 twist. Somewhere in one of the post I read that the lighter rounds might be less accurate in a 1/7 twist barrel. Your response here is really condensed and informative for any newbie like me.

Thanks alot I appreciate the help, I will be going the the 1/7 twist.

[drclark]

Depends on what your goals are.

My girlfriend's AR is built up with a 16" 1-7 twist. Mine is a 20" 1-9 twist. Both are chrome-lined. Both were purchased from Del-ton.

So far we have only shot 55gr out of both. I would say that the 20" is only slightly more accurate at 100yds using iron sights but that may be due more to barrel weight and the increased sight radius of the 20" over the 16".

We mostly plink with our AR's and are sufficiently satisfied with their accruacy (1-2 MOA, usually 1 MOA when we do our part). As far as I can tell there is no real meaningful difference between the two twist rates with 55gr ammo. However, if your intent is to shoot clover-leaf groups or shoot competitions then you might care about the difference.

Maybe next time we take them to the range, I will shoot each one for groups and post pictures.

drc

[Prc329]

Theoretically,
1x7 shoots anything from 50gr - 77gr and to even heavier ones like 80gr and 90gr(but 80/90 are not magazineable)
1x9 shoots anything from 40gr - 69gr

With that being said, you can shoot heavier bullets in a 1x9 and lighter in a 1x7. Your mileage may vary. There is no virtual guarantee of stabilization when shooting as stated above. I have personally shot 75 grain threw a 1x9 and it did o.k. I think I got lucky and had a batch of wolf gold that just loved all my guns.

[Jicko]

PS. at one point(from my personal experience), I have a 16" M4 profile Stag chrome-lined 1x9 and a 16" M4 profile Colt chrome-lined 1x7. I put the 9x scope of both and shot 2 5 rounds string @ 50yds w/ Federal AE223(55gr FMJBT, .223 SAMMI spec) ammo from a benchrest. There is virtually NO difference in terms of groupings/accuracy between the 2.

I ended up keeping the Colt 1x7 and sold the Stag 1x9.

With that being said, you can shoot heavier bullets in a 1x9 and lighter in a 1x7. Your mileage may vary. There is no virtual guarantee of stabilization when shooting as stated above. I have personally shot 75 grain threw a 1x9 and it did o.k. I think I got lucky and had a batch of wolf gold that just loved all my guns.

+1 So, if you *already* have a barrel, before you rush out, dump yours and acquire another one.... your best bet is to "try out" rounds that are outside of the "theoretical" limit.... and you may get lucky.... (I m currently working on a 77gr MK262 load for a 1x7 SPR barrel, once I get closer to nailing down the recipe, I'd try those rounds in a 24" 1x9 bull barrel I have and see if I get lucky there.... one way or the other, I'll post result pics, stay tuned!)

Yet if you are to buy a new barrel/upper, then you can use those limits as a guideline, and make a choice between 1x7 or 1x9. BTW, CMMG are good stuff! (And unless you are trying for extreme accuracy, get "chrome-lined" barrels)

[6172crew]

Our military went with the 1/7 twist to stabilize the 69 grain tracer rounds or M855/SS109 round.

The only problem with that round is its not ok to shoot those at most CA ranges because of fire hazards so you find the 55 grain XM193 rounds sold which will work out of the 1/7 or 1/9 but they say the 55 grain works better in the 1/9 out to 200 meters? (not 100% on that last statement but it follows the basic rule of thumb).

Good luck with you r rifle build dont forget to stop by the other pages at CalGuns so you can help us fight these wacky laws they are trying to push on us this year.

[Prc329]

I thought tracers were illegal in california?

[Mute]

Just get a 1:8 twist barrel.

[tenpercentfirearms]

Yes tracers are illegal in the State of California. It is not a fire hazard thing, it is a straight up go to jail thing.

[Sig357]

Just get a 1:8 twist barrel.

A 1/8 twist barrel may be an option, kind of the best of both worlds. Thanks for all the help guys. Now if only I could find one without a huge lead time.

[WolfMansDad]

Bullets need spin to stabilize. A bullet spun too slowly will tumble end over end, or wobble like a "wounded duck" pass in football. Wobbling or tumbling leads to significant loss of accuracy and velocity, because of the resulting irregular air resistance. A stabilized bullet slips through the air like an olympic diver entering the water. The water (or the air in the case of the bullet) doesn't affect his trajectory much at all. A tumbling bullet hits the air like a belly flop. Big difference. And air resistance is significant. A .223 bullet experiences 9,000 gees (that's nine thousand gravities) of deceleration in the first hundred yards of its flight.

The amount of spin a bullet needs depends on its length. Longer bullets (which also happen to be heavier, for the same caliber) require a faster spin. You can't over-spin a short (light) bullet, but you can under-spin a long (heavy) one. Your 55 grain bullets will do just fine in a 1:7 twist, but the 77 grain bullets might not stabilize in a 1:9 barrel.

[Lon Moer]

I can't believe nobody has posted this; ammo-oracle.com