The Firing Line Forums

Go Back   The Firing Line Forums > The Hide > The Art of the Rifle: General

Reply
 
Thread Tools
Old February 13, 2012, 02:57 PM   #1
blacksky
Senior Member
 
Join Date: November 21, 2008
Location: OH
Posts: 735
300 AAC Blackout Barrel Questions...

I'm going to convert one of my AR'S to the 300 AAC Blackout.

Any barrel recommendations?

Length 16" to 20"?

What twist rate?

Which is the most accurate out to 300 yards?
__________________
By the choices we make, we define ourselves, thereby revealing what we truly care about.
blacksky is offline  
Old February 13, 2012, 03:54 PM   #2
taylorce1
Senior Member
 
Join Date: November 18, 2005
Location: On the Santa Fe Trail
Posts: 5,353
Barrel length doesn't really affect accuracy much between a 16.5" and 20" barrels. If you aren't using optics then the longer barrel should provide slightly better accuracy. The AAC BLK is designed around a 1:8 twist barrel, since the heavy bullets are moving so slow you need a faster twist to stabilize the bullets.
__________________
NRA Life Member
The Truth About Guns
taylorce1 is offline  
Old February 13, 2012, 03:59 PM   #3
rjrivero
Senior Member
 
Join Date: November 17, 2008
Location: NW Ohio
Posts: 1,348
The "new" 300 Blackout barrels are going 1:7 Twist for the subsonic 220+ bullets designs that will expand at subsonic velocities.

Personally, i don't see any benefit with going longer than 16" in this caliber.
rjrivero is offline  
Old February 13, 2012, 04:00 PM   #4
Palmetto-Pride
Senior Member
 
Join Date: May 31, 2009
Location: Charleston, SC
Posts: 1,874
Good luck finding a barrel longer than 16" for the 300 Black Out.
__________________
“The problem with socialism is that you eventually run out of other people's money.”

-Margaret Thatcher-
Palmetto-Pride is offline  
Old February 13, 2012, 04:47 PM   #5
RT
Senior Member
 
Join Date: September 9, 2000
Location: San Antonio, TX
Posts: 2,191
I believe th BLK is optimized for a SBR so 16 inches should be plenty.
RT is offline  
Old February 13, 2012, 04:56 PM   #6
blacksky
Senior Member
 
Join Date: November 21, 2008
Location: OH
Posts: 735
Good luck finding a barrel longer than 16" for the 300 Black Out.

http://www.tacticalammunition.com/30...-TA88-0330.htm

16" to 24" barrels with 1-8.5, and 1-11 twist rates???

http://www.tacticalammunition.com/30...-TA88-0334.htm
__________________
By the choices we make, we define ourselves, thereby revealing what we truly care about.

Last edited by blacksky; February 13, 2012 at 11:59 PM.
blacksky is offline  
Old February 13, 2012, 06:27 PM   #7
rsilvers
Member
 
Join Date: January 16, 2011
Posts: 71
A 16 inch 300 BLK has as much energy as a 24 inch 5.56mm. There are velocity gains past 16 inches, not it is diminisning - Daniel Horner used a 20-22 inch:

http://bulletin.accurateshooter.com/...gun-nationals/

That being said, I would go with 16 as it is the sweet spot.
rsilvers is offline  
Old February 13, 2012, 06:31 PM   #8
Toxdoc
Senior Member
 
Join Date: June 5, 2008
Posts: 106
Quote:
18" barrels with 1-8.5, and 1-11 twist rates
Those choice will likely limit you to supersonic ammo, although the 1:8.5 would probably be ok. It is definitely a non-standard twist rate.

AAC recommended a 1:8 and is going to a 1:7 as noted above.

For that kind of money, you can get a barrel from Wilson Combat: http://shopwilsoncombat.com/300-AAC-.../products/397/
Toxdoc is offline  
Old February 13, 2012, 06:31 PM   #9
Nitesites
Senior Member
 
Join Date: March 28, 2011
Posts: 600
Congrats!
__________________
On Yellow
Nitesites is offline  
Old February 13, 2012, 07:46 PM   #10
taylorce1
Senior Member
 
Join Date: November 18, 2005
Location: On the Santa Fe Trail
Posts: 5,353
I had to check on the twist rate and it seems to be more of a stabalization issue in SBR's than getting bullets to expand. The 220+ bullets are stabalized better at longer ranges out of a 1:7 twist in SBR barrels. From the littel I was able to research on it it seems that the 1:7 twist might not be of any benifit in a longer barrel. The SAAMI specs are still a 1:8 twist and I doubt anyone will get that changed anytime soon.
__________________
NRA Life Member
The Truth About Guns
taylorce1 is offline  
Old February 13, 2012, 09:26 PM   #11
rsilvers
Member
 
Join Date: January 16, 2011
Posts: 71
No one is going to attempt to change the SAAMI suggested twist rate - there is no need to as it is just a suggestion.
rsilvers is offline  
Old February 13, 2012, 10:59 PM   #12
blacksky
Senior Member
 
Join Date: November 21, 2008
Location: OH
Posts: 735
Good luck finding any in stock...

No one seems to have any 16" in stock???
__________________
By the choices we make, we define ourselves, thereby revealing what we truly care about.
blacksky is offline  
Old February 14, 2012, 03:55 PM   #13
blacksky
Senior Member
 
Join Date: November 21, 2008
Location: OH
Posts: 735
I would think that the 11-1 twist would stabilize the bullett while adding increased

So there is no advantage to a longer barrel with a 11-1 twist rate? What about a 24" barrel? I would think that the 11-1 twist would stabilize the bullett while adding increased distance to the range...
__________________
By the choices we make, we define ourselves, thereby revealing what we truly care about.
blacksky is offline  
Old February 14, 2012, 06:17 PM   #14
taylorce1
Senior Member
 
Join Date: November 18, 2005
Location: On the Santa Fe Trail
Posts: 5,353
With the .300 Blackout there isn't going to be any advantage to a longer barrel out to 24". You can't cram enough slow burning powders into the case to take advantage of the length, and fast burning powders will be used up before the bullet exits the barrel. Anything over 16-20" isn't going to gain you anything.

For example my little 6mmX47 (6-222 Rem Mag) with a 20" barrel is only 25 fps behind the Sierra manual loads out of a 26" barrel. That tells me I didn't need a 6" longer barrel as I wouldn't gain anything. So I got a lighter and better handling rifle by going with a shorter barrel.
__________________
NRA Life Member
The Truth About Guns
taylorce1 is offline  
Old February 14, 2012, 06:19 PM   #15
rsilvers
Member
 
Join Date: January 16, 2011
Posts: 71
A longer barrel has more velocity. But a 16 inch 300 BLK barrel already is sucking the juice out of the cartridge as much as a 5.56mm does with a 24 inch barrel.

So if you are the type of person who wants a longer-than-24 inch 5.56mm barrel, then you would also want a longer than 16 inch 300 BLK barrel.
rsilvers is offline  
Old February 14, 2012, 06:26 PM   #16
rsilvers
Member
 
Join Date: January 16, 2011
Posts: 71
300 BLK does gain velocity up to and past a 30 inch barrel.



Barrel length has virtually no effect on which powder to use to get the most velocity. I know it is commonly believed to be the case, but it just does not really work that way. It does a little, but primarily whatever powder gives the most velocity in a 6 inch barrel with probably also give the most velocity in a 24 inch barrel. This is because the powder that reaches peak pressure and velocity for any given bullet weight does so within the first inch of bullet travel.

300 BLK will gain about 65 fps per inch at around 9 inches, 43 fps per inch at around 12 inches, 28 fps per inch at around 16 inches, 21 fps per inch at around 20 inches, 17 fps per inch at around 24 inches, and 12 fps per inch at around 30 inches. You just need to decide where you want to stop.

Last edited by rsilvers; February 14, 2012 at 06:31 PM.
rsilvers is offline  
Old February 14, 2012, 09:01 PM   #17
Justice06RR
Senior Member
 
Join Date: December 21, 2010
Location: Central FL
Posts: 1,242
1:8 is standard for 300Blackout, but damn I can't find any 16in barrels in stock. Its better to just buy a complete 300 upper instead. Somehow they are not making these barrels fast enough?
Justice06RR is offline  
Old February 14, 2012, 09:34 PM   #18
blacksky
Senior Member
 
Join Date: November 21, 2008
Location: OH
Posts: 735
I got a lighter and better handling rifle by going with a shorter barrel

Like I said in the first post, I am blind here... So there's no difference in velocity and energy between 16" to 20" other than additional barrel weight? Will the 300AAC reach out to 300 yards with enough energy to hunt with? If so in what configuration? If not what is the max effective range?
__________________
By the choices we make, we define ourselves, thereby revealing what we truly care about.
blacksky is offline  
Old February 14, 2012, 09:42 PM   #19
Abel
Senior Member
 
Join Date: November 26, 2006
Posts: 1,161
Quote:
Like I said in the first post, I am blind here... So there's no difference in velocity and energy between 16" to 20" other than additional barrel weight? Will the 300AAC reach out to 300 yards with enough energy to hunt with? If so in what configuration? If not what is the max effective range?
I would think that this round is kin to a 30-30 in performance. In other words, its more of a 200 yard deal. If you want to get out to 250+ yards with flat trajectory, a 220gr projectile may not be what you want. So, a 1:9" or 1:10" would stabilize a smaller projectile, say 150gr or 165gr.
Abel is offline  
Old February 14, 2012, 11:27 PM   #20
taylorce1
Senior Member
 
Join Date: November 18, 2005
Location: On the Santa Fe Trail
Posts: 5,353
Yes the .300 BLK will reach 300 yards, as to having enough energy to hunt with you'll have to decide.

125 grain Sierra OTM bullet
MV 2200 fps, velocity at 300 yards 1536 fps energy 656 ft-lbs.

240 grain Sierra MK bullet
MV 1000 fps, velocity at 3000 yards 922 fps energy 453 ft-lbs.

At 300 yards the 240 grain bullet would be like shooting a deer with a muzzle loader. I wouldn't hesitate to take a deer with either at 300 yards but I would prefer much closer. I do like the fact that the heavier bullet doesn't even loose 100 fps in 300 yards from the muzzle, so maybe a 165 grain bullet like the Accubond would be a great compromise, loose a little MV but pick up more energy out to 300 yards.
__________________
NRA Life Member
The Truth About Guns
taylorce1 is offline  
Old February 15, 2012, 01:16 PM   #21
rsilvers
Member
 
Join Date: January 16, 2011
Posts: 71
"So there's no difference in velocity and energy between 16" to 20" other than additional barrel weight?"

2400 fps vs 2491 fps.
1403 ft-lbs vs 1515 ft-lbs.

"Will the 300AAC reach out to 300 yards with enough energy to hunt with?"

Yes - energy and bullet performance is fine at 300 - but the drop at 300 is about 11 inches from a 200 yard zero - so if you want to shoot beyond 300 yards - you will have to start to do scope adjustments or holdover.

If you want to hunt long range - 308 is the way I would go.

"If so in what configuration?"

A 9 inch barrel is good for up to 300 yards for hunting based on bullet performance. A 6 inch barrel I would limit to 200 yards.

"If not what is the max effective range?"

For hunting I would say 300 yards. For military use and by M4 standards based on hit probability, it is 440 meters from a 9 inch barrel and 460 meters from a 16 inch barrel. This is because those are the ranges for which the wind drift and drop matches the M4 at its stated max effective range.
rsilvers is offline  
Old February 15, 2012, 05:13 PM   #22
blacksky
Senior Member
 
Join Date: November 21, 2008
Location: OH
Posts: 735
So what would you recommend in a barrel for a AR conversion?

I can get 16" to 24" in either .750 or .920 diameter at the muzzel,
with 8 - 8.5 -11 to 1 twist rates.

I'm trying to squeeze as much out of this conversion as I can.

I already have a M24.308 5R and just got a .338 WINMAG for long distance.

I have 2 AR'S that will ring steel at 600yards and I'm wanting a 300AAC BLK with all I can get from it.
__________________
By the choices we make, we define ourselves, thereby revealing what we truly care about.
blacksky is offline  
Old February 15, 2012, 09:56 PM   #23
rdmallory
Senior Member
 
Join Date: February 10, 2009
Location: Deltona FL
Posts: 952
Check Midway. That is where I picked mine up from.

Doug
rdmallory is offline  
Old February 16, 2012, 11:37 AM   #24
blacksky
Senior Member
 
Join Date: November 21, 2008
Location: OH
Posts: 735
Check Midway. That is where I picked mine up from.

Out of stock!
__________________
By the choices we make, we define ourselves, thereby revealing what we truly care about.
blacksky is offline  
Reply

Thread Tools

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT -5. The time now is 01:48 PM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2014, vBulletin Solutions, Inc.
This site and contents, including all posts, Copyright © 1998-2014 S.W.A.T. Magazine
Copyright Complaints: Please direct DMCA Takedown Notices to the registered agent: thefiringline.com
Contact Us
Page generated in 0.15581 seconds with 7 queries