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Mxpatriot51
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Posted: 9/13/2007 8:55:07 PM
[Last Edit: 9/13/2007 9:15:06 PM by Mxpatriot51]
Where do you stand on this? The only place I see the 24'' have the advantage is at 400+ yards, because that's when FPS starts to really matter with a .223. I'd like to be able to take the rifle out to 600 accurately (I'd be happy with a .75 to 1 MOA group at that distance) and be in the neighborhood at 700. I'm trying to avoid going trans-sonic.

Bushmaster states a 100 FPS difference between the two with factory ammo.

What I'm really comparing buying for my build is the 1/9 twist 24'' varminter barrel by Bushmaster or the 1/8 twist 20'' Predator barrel by Bushmaster. Neither of these are chrome lined, but that's okay with me.

I've heard that with some loads in .308 that there is practically no velocity gain in a barrel longer than 20''. Can this be done with .223? I'm a reloader, so I can switch to whatever powder is needed to get a burn rate to achieve maximum velocity in 20'' instead of 24''.




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txgp17
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Posted: 9/13/2007 9:03:37 PM
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Posted: 9/13/2007 9:38:44 PM
20" with a 1:8. I'd also recommend you look at PKFirearms and find 18" sabre defense barreled upper with a 1:7 twist.

You'll be able to shoot any bullet that fits in that fits in the magazine.

Heavier bullets will buck the wind a bit better for long range shooting.

1:7 will allow you to shoot the heaviest bullets that have to be single fed.

Varget is my go-to powder for long range accuracy in an AR.

For varminting where you'll need to carry the rifle, the 20" or an 18" works great and doesn't add un-utilized weight. I assume you'll have a bipod and a 40-50mm scope which adds some weight to lug around.
WarNerve
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Posted: 9/13/2007 9:42:03 PM
Twenty is plenty.
Border_Ruffian
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Posted: 9/13/2007 9:43:46 PM
[Last Edit: 9/13/2007 9:48:45 PM by Border_Ruffian]
Well, since you are talking 700 yard shots, I imagine you will be firing supported prone or from a bench. If that is what this baby will be doing most of the time. I would go for the 24" bbl. The way I understand it you will always get more velocity from a 24" bbl with a given load fired from a 20" bbl. Also the extra weight will help you keep your sight picture. Edited to say 24" bbl with at least a 1 in 8 twist you will want the heavier rounds to help buck wind.
newby
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Posted: 9/13/2007 9:44:45 PM
A 20 incher shoots accurately at 600 with no problems...but in the wind, the 24" inch will give a slight advantage.
Mxpatriot51
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Posted: 9/13/2007 11:01:25 PM
The rifle will not be carried much, mostly a bench/prone rifle with the occasional precision tactical match.

I'd like to be sticking with magazine length bullets and loads, and be able to shoot lighter 55 grain bullets at 100 yards when there isn't any wind.

I just found 20'' fluted SPR barrel from White oak with a 1:8 twist. Looks like it might be the ticket.

I don't really like the look of the 24'', but that extra 100 FPS would be nice to beat the wind at longer distances.

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Mxpatriot51
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Posted: 9/13/2007 11:03:18 PM
With a 1:7 twist, what would be the lightest bullet that would be accurately stabilized?

With a 1:8?

What's the heaviest I can get to be accurate out of a 1:9?

thanks
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bigbore
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Posted: 9/13/2007 11:32:43 PM
20" 1:7 80gr Bergers, 1000 yds

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Mxpatriot51
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Posted: 9/13/2007 11:51:45 PM

Originally Posted By bigbore:
20" 1:7 80gr Bergers, 1000 yds
www.adcofirearms.com/junkpics/20at1k.jpg


What kind of grouping can that rifle get at 1,000? (given an experienced shooter behind the trigger)

And that's with irons, I'd imagine a 14X scope would be a great aid at that distance.

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bigbore
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Posted: 9/14/2007 7:22:17 AM

Originally Posted By Mxpatriot51:
What kind of grouping can that rifle get at 1,000? (given an experienced shooter behind the trigger)

And that's with irons, I'd imagine a 14X scope would be a great aid at that distance.



My rifle is capable of the 1 MOA X-Ring, but there are many variables the shooter needs to REALLY watch. The Farr Trophy - Service Rifle, was won by someone(I believe a friend of newby's) who shot 77gr bullets last year...
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Phoebus
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Posted: 9/14/2007 8:00:28 AM

Originally Posted By Mxpatriot51:
With a 1:7 twist, what would be the lightest bullet that would be accurately stabilized?

With a 1:8?



Bullets do not become less-stabilized as they get lighter, only heavier. If a barrel can stabilize a round, it can do anything lighter (well, shorter acutally).

The main reason that light bullets can have problems in a fast twist is if there are imperfections in the round. A high-velocity light bullet in a fast twist is doing a lot of RPMs. If the bullet has defects that make its SD imperfectly distributed, then it will destabilize a bit as you go faster rotationally.




What's the heaviest I can get to be accurate out of a 1:9?

thanks


Probably 69gr or so.
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Posted: 9/14/2007 8:24:44 AM

Originally Posted By bigbore:
20" 1:7 80gr Bergers, 1000 yds
www.adcofirearms.com/junkpics/20at1k.jpg


The 80 gr. Berger's not a mag-length bullet is it?
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newby
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Posted: 9/14/2007 9:10:06 AM
Most 20" 9 twist tubes will shoot the Hornady 75 BTHP ok but not many will stabilize the Sierra 77. The problem with light bullets in fast twist barrels isn't that they destabilize, its that they turn into a white puff of lead and shrapnel shortly after they leave the barrel. 55 grainers will be fine in a 20" 7 twist as long as you don't push them much past 3200 fps. I wouldn't try anything lighter than that though.
newby
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Posted: 9/14/2007 9:20:13 AM

Originally Posted By bigbore:

Originally Posted By Mxpatriot51:
What kind of grouping can that rifle get at 1,000? (given an experienced shooter behind the trigger)

And that's with irons, I'd imagine a 14X scope would be a great aid at that distance.



My rifle is capable of the 1 MOA X-Ring, but there are many variables the shooter needs to REALLY watch. The Farr Trophy - Service Rifle, was won by someone(I believe a friend of newby's) who shot 77gr bullets last year...


Actually, Joe is the only shooter to win the Farr in the last 5 years that I DON'T know. If he runs with Sylvester, we've probably met though.
newby
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Posted: 9/14/2007 9:21:59 AM

Originally Posted By SPTiger:

Originally Posted By bigbore:
20" 1:7 80gr Bergers, 1000 yds
www.adcofirearms.com/junkpics/20at1k.jpg


The 80 gr. Berger's not a mag-length bullet is it?


Not even close
Mxpatriot51
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Posted: 9/14/2007 10:52:44 AM

Originally Posted By Phoebus:

Originally Posted By Mxpatriot51:
With a 1:7 twist, what would be the lightest bullet that would be accurately stabilized?

With a 1:8?



Bullets do not become less-stabilized as they get lighter, only heavier. If a barrel can stabilize a round, it can do anything lighter (well, shorter acutally).

The main reason that light bullets can have problems in a fast twist is if there are imperfections in the round. A high-velocity light bullet in a fast twist is doing a lot of RPMs. If the bullet has defects that make its SD imperfectly distributed, then it will destabilize a bit as you go faster rotationally.




What's the heaviest I can get to be accurate out of a 1:9?

thanks


Probably 69gr or so.


So I'm thinking a 1:8 twist will be right for me. It'll let me shoot 55 grain bullets at 3300 FPS and also allow heavier bullets for longer ranges/heavier winds.

Now how about 20" vs. 24'' in terms of velocity. Is it worth it to have that extra 4''?
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Posted: 9/14/2007 10:21:04 PM

Originally Posted By Mxpatriot51:

Originally Posted By Phoebus:

Originally Posted By Mxpatriot51:
With a 1:7 twist, what would be the lightest bullet that would be accurately stabilized?

With a 1:8?



Bullets do not become less-stabilized as they get lighter, only heavier. If a barrel can stabilize a round, it can do anything lighter (well, shorter acutally).

The main reason that light bullets can have problems in a fast twist is if there are imperfections in the round. A high-velocity light bullet in a fast twist is doing a lot of RPMs. If the bullet has defects that make its SD imperfectly distributed, then it will destabilize a bit as you go faster rotationally.




What's the heaviest I can get to be accurate out of a 1:9?

thanks


Probably 69gr or so.


So I'm thinking a 1:8 twist will be right for me. It'll let me shoot 55 grain bullets at 3300 FPS and also allow heavier bullets for longer ranges/heavier winds.

Now how about 20" vs. 24'' in terms of velocity. Is it worth it to have that extra 4''?


i had the same debate about 6 months ago, and i decided on a 24" 1x8 barrel, a JP to be specific with that big ass compensator they have . i have been waiting paitiently for those 6 months, but i have plenty of other toys to keep myself occupied in the mean time. whenever they get around to making that barrel i will be all over it.

20" would prolly work fine for me, but i already have a 20 incher, wanted something different.
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Posted: 9/14/2007 10:27:04 PM
I just want to add that a 1:7 barrel will stabalize a 55gr bullet just fine.

Otherwise, I have nothing to add. My longest range shooting is 300 yards with a 10.5" bbl. I did 2.5MOA though
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Posted: 9/14/2007 11:02:38 PM
After trying at least 8 different barrels from as many vendors, I have decided nothing is better than Shilen 24" or Krieger. The Shilen are 1 in 8" twist with target crown. The Kriegers are i in 7" with target crown. Any of these will shoot into one hole at 100 yds. using Black Hills 77 grn. Match ammo. I have found nothing better. jb