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Centerfire Rifles - Semiautomatic or Gas Operated Centerfire rifles, carbines and other gas operated rifles.

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  #1  
Old 10-27-2008, 9:16 PM
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Default 1/7 twist vs. 1/9 twist

1/7 twist vs. 1/9 twist. Can someone explain the pro's and con's of each? I have heard that one of them can shoot a wider variety of ammo, which one is it? Also my Stag upper is 1/9 twist. What grain ammo is better for the 1/9 twist rate?



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  #2  
Old 10-27-2008, 9:32 PM
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1/9 can shoot a wider range of bullets. Usually from 45gr to 65-70gr.

1/7 is made to shoot heavier bullets.

(And man its been awhile since I really posted and caught up on my info, so if for some reason I'm incorrect feel free to let me know .)

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  #3  
Old 10-27-2008, 9:32 PM
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1/9 twist is better for lighter, shorter cartridges (62 grain and below).
1/7 twist is superior for heavier, longer cartridges (62 grain and above).

Bullet weight isn't the actual factor, bullet length is. As for what's superior, that seems to be debatable with the 1/7 twist being preferred by most.
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Old 10-27-2008, 9:41 PM
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1-9 will shoot 55-62 fine if your looking to shoot long range 69SMK works best for me, I have been able to shoot 75-77 gr with great accuracy at 5000ft elevation but at lower altitude I go lighter over all 69SMK gives me the best results. 1-7 works great using 55-77 gr. Unless your reloading you would not know the difference. I your are looking for 55-69gr 1-9 is fine if your looking long range heavy rounds 1:7 is better
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Old 10-27-2008, 11:41 PM
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1:8 isn't a bad way to go either. It won't shoot as light a bullet as the 1:9 twist but it will shoot the 77's just fine, and lighter bullets than the 1:7.

I'm basing this on shooting 10" plates out to 400 yards. If you were shooting for group that might be different.
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Old 10-28-2008, 12:38 AM
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1:7 is necessary to stabilize military L110 tracer rounds - that's why the military uses it. It is also a better choice for stabilizing the heavy stuff.

1:9 is common in commercial AR's and will shoot some of the lighter varmint .223 stuff.

1:12 and 1:14 are for the lightweight varmint bullets. Interestingly though, the original M16's (Colt 601) had 1:14 twist ratios. This was changed to 1:12 with the adoption of the Colt 602, then the original M16. It was later changed to 1:9. It was only with NATO standardization in the late 70's that the 1:7 twist ratio came about - this was because of the tracer issue.

Both will shoot 55gr and 62gr ball just fine. 1:9 will also shoot the 69gr match stuff with no probs. The 75gr and 77gr match stuff is at the limit of being stabilized with 1:9 twist though. I have never shot 77gr out of a 1:9 but I have heard of (but never seen) keyholing with 77gr bullets out of shorter 1:9 barrels at longer ranges.

Both are appropriate for general use. It is when you get into the specialized bullets that it really becomes an issue. The super long 80gr and 90gr match bullets used by the 100yd crowd need a 1:7 or so twist to be stabilized. These bullets will not load in an AR magazine and must be single loaded. They are fun for 600yds plus though!

The super light varmint bullets will be spun way too fast by a 1:7. I have read about (but never seen) the little 40gr and under bullets being spun so fast that the jacket strips itself off by 1:7 twist. Might not be as much an issue with solids though - I really have no idea here.

Hope that helps,
-Pete
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Old 10-28-2008, 5:43 AM
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Interesting... so what are the consequences of firing a 55 grain bullet through a 1:7 twist barrel exactly? Is there simply a reduction in accuracy at a certain range? Or is it something more severe? Will it be noticeable within 100 yards?
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Old 10-28-2008, 6:07 AM
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Here is a pro for shooting a 1-9. Ammo is cheaper.
Black Hills charges $100 more for a case of 75/77 than they do 68/69 gr bullets.
With a 1-9 if you are shooting under 400 yards, black hills 52 match hp, 60 vmax, 68 otm and 69 sierra otm will work great and cheap off the shelf 55 fmj stuff will also work good
If you want to shoot at say 600-1000 yards, many people step up to the 75/77 gr bullets with a faster 1-8 or 1-7 twist.

My last 1-9 upper was accurate with 75gr ammo but it was overkill for under 400 yards. The 52s and 60s have higher velocity and don't drop as fast.
I don't use 75s for matches anymore but still have a few boxes for SHTF because they have great terminal ballistics.

If I were you, I'd buy a box or two of some 75s just to see what they do in YOUR rifle accuracy wise, but then I would buy the lighter, quicker, and cheaper bullets for accuracy work and stick to 55 fjm for blasting ammo.
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Old 10-28-2008, 6:17 AM
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PM sent
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  #10  
Old 10-28-2008, 7:47 AM
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Quote:
Originally Posted by civilsnake View Post
Interesting... so what are the consequences of firing a 55 grain bullet through a 1:7 twist barrel exactly? Is there simply a reduction in accuracy at a certain range? Or is it something more severe? Will it be noticeable within 100 yards?
stress on your rifling the higher the fps& RPM's the more stress on the barrel.
If you fire a hot load using a 40gr out of a long barreled .223 with 1/7 all you will see is a puff of smoke ( the bullet ripping it self apart by RPM's)
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Old 10-28-2008, 8:02 AM
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stress on your rifling the higher the fps& RPM's the more stress on the barrel.
If you fire a hot load using a 40gr out of a long barreled .223 with 1/7 all you will see is a puff of smoke ( the bullet ripping it self apart by RPM's)
It's only a 16 inch barrel, so I imagine it wouldn't be considered "long".

I'm assuming I should be okay with a 1:7 twist 16" barrel firing 55 grain. But will there be a noticeable decrease in accuracy if the bullet is spinning too fast?

I'm curious because I went to a gun show and bought 1000 rounds of (I believe) 55 grain to be able to plink with and get a feel for the rifle. I haven't shot a rifle in probably 10 years and wanted to have cheap ammo to practice. Is this going to be a problem?
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  #12  
Old 10-28-2008, 9:41 AM
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Quote:
Originally Posted by civilsnake View Post
It's only a 16 inch barrel, so I imagine it wouldn't be considered "long".

I'm assuming I should be okay with a 1:7 twist 16" barrel firing 55 grain. But will there be a noticeable decrease in accuracy if the bullet is spinning too fast?

I'm curious because I went to a gun show and bought 1000 rounds of (I believe) 55 grain to be able to plink with and get a feel for the rifle. I haven't shot a rifle in probably 10 years and wanted to have cheap ammo to practice. Is this going to be a problem?
Don't worry, 1:7 will shoot 55gr bullets just fine. All of my 5.56 barrels are 1:7 twist and I've shot so much XM193, Q3131A and M855 (62gr) that my wallet cries when I think about it.

Between 1:7 and 1:9 I always pick 1:7 as it will guarantee better performance with longer heavier bullets, if you choose to use them.
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  #13  
Old 10-28-2008, 10:01 AM
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You only need to ask yourself ONE question.... are you going to shoot those 50gr or 40gr Varmit bullets? If not... 1:7 is your best bet....

Most of us probably will minimally shoot 55gr.... those are "fine" with 1:7 barrel... and with a 1:7, you can go all the way up... 77gr, 80gr... but a 1:9 will probably not going to do 77gr well, if even possible (unless you have a LONG barrel, 24"....)

I did over generalize a bit.... there are slight accuracy issue one verse the other... also not all 1:9 are REALLY 1:9... the same as not all 1:7 are REALLY 1:7.....

So, YMMV...... but in short.... 1:7 is more "universal" than 1:9, IMO.... we are talking about shooting 55gr to 77gr..... 2 of the most popular 223/556 out there... XM193(55gr), Mk262(77gr)
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Old 10-28-2008, 1:30 PM
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Mk262 isn't "popular" by round count.

By far the two most used loads are M193 and M855. Probably by 100:1 over anything else.

Mk262 is popular because of its long range performance and ability to frag even from even extremely short barrels. Its terminal performance is simply hard to beat. Given its cost, and scarcity, most people shoot small amounts of Mk262. It's almost impossible to find on the market right now, too. If you reload, though, you can make your own version.

I'm of the opinion 1/8 is the best choice. 1/7 or 1/9 is generally more available in combat-style rifles. One issue for me is most 1/9 guns use improper barrel steel (not 4150-mil).

In the end, for me, the ability to use Mk262 and tracers wins over the ability to shoot lighter varmint rounds or M193 to perfection.

Everything is a compromise.
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Old 10-28-2008, 1:36 PM
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+1 to uclap...

Mk262, the real thing, are just hard to find. But I kinda us that to mean 77gr HPBT bullet... i dont know of any particular load that is too "popular" below the 55gr M193.

When I said it is popular... is that, for civilian, a lot of shooters are trying to shoot 77gr HPBT SMK for its long(er) range potential.... they are probably NOT shooting real Mk262... but *similar* load...

And for the military, Mk262 has proven performance over M193 and M855.... even on shorter barrel rifles....
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Old 10-28-2008, 2:22 PM
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Quote:
Originally Posted by civilsnake View Post
Interesting... so what are the consequences of firing a 55 grain bullet through a 1:7 twist barrel exactly? Is there simply a reduction in accuracy at a certain range? Or is it something more severe? Will it be noticeable within 100 yards?
...It's only a 16 inch barrel, so I imagine it wouldn't be considered "long".
I'm assuming I should be okay with a 1:7 twist 16" barrel firing 55 grain. But will there be a noticeable decrease in accuracy if the bullet is spinning too fast?
+2 to everything Jicko and Plinker said.

Consider that the most common military loads are 55gr and 62gr. Probably 90%+ of all military 5.56NATO chambered rifles have a 1:7 twist these days. Shooting 55gr out of a 1:7 twist is fine. It is what the military does all day long.

That said, there are plenty of people that argue tat you will get slightly better accuracy shooting 55gr out of 1:8 or 1:9 twist barrels. It is probably not enough to matter for your purposes. Generally you figure that 55gr and 62gr are your bulk buy bargain ammo. 69gr and 75/77gr are your match ammo. A 1:7 - 1:8 twist is the best compromise for shooting that range of bullets.

If you are thinking of shooting sub 40 gr varmint grenades or 80+gr palma bullets, well that is another discussion...
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Old 10-28-2008, 3:22 PM
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Where can a person even get mk 262? I've done a little searching and haven't found it online. Does Black Hills make something equivalent under a different name for civilian use?
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Old 10-28-2008, 3:53 PM
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Where can a person even get mk 262? I've done a little searching and haven't found it online. Does Black Hills make something equivalent under a different name for civilian use?
Real MK262 is close to non-existence in the civilian market...

Just get BHA red box 77gr HPBT... they are "close enough".... not as HOT, but close enough...
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Old 11-01-2008, 8:56 AM
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Where can a person even get mk 262? I've done a little searching and haven't found it online. Does Black Hills make something equivalent under a different name for civilian use?
Never seen it. I know a couple guys that handload 77gr Sierra HPBT for their rifles though.

There is also the 77gr Federal GMM

Another option is the Prvi Partisan 75gr Match stuff. That is usually pretty inexpensive in comparison (~$80-$90/200rds + shipping last time I checked). I've never tried it, but their 168gr .308 match works quite well. It should have similar ballistics.

The mk262 mod 0 is just 77gr SMK if IIRC. The mod 1 stuff has additional things done to increase wound potential. From a ballistics standpoint for punching paper, just find whichever 77gr load works best in your rifle. For wounding potential, civilians aren't bound by the same restrictions as .mil, so imho you would be better off buying TAP or frangible or whatnot.
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Old 11-01-2008, 9:07 AM
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The 1/9 is good for general recreational use with the 55-62 grain issue ammo or equivalent.

The 1/7 twist wil stabilize "the good stuff" (read as $) and if you don't want to spend $600.00 a K for ammo, go with the 1/9.
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  #21  
Old 11-01-2008, 6:17 PM
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Get a 1:8 wylde and shoot everything. That's what I did - after lots of reading.
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