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ILoveMyAR
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Posted: 3/18/2013 1:52:15 AM
What's the max range the 6.8 can handle with out to much trouble and not being effected by natural ellements much?

Out of say a 14.5 or 16" barrel!


Thanks
reelserious
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Posted: 3/18/2013 5:44:30 AM
[Last Edit: 3/18/2013 5:45:00 AM by reelserious]
A couple of weeks ago I was hitting a 8 inch gong at 400 yards every time with the 120 grain Hornady SST.


10 MOA comeup from a 100 yard zero.
jukeboxx13
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Posted: 3/18/2013 6:44:23 AM
I would guess 500 yards since that is around the max range of 5.56.
eracer
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Posted: 3/18/2013 7:37:46 AM
I'd say 500 yards.
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Slateman
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Posted: 3/18/2013 7:56:14 AM
[Last Edit: 3/18/2013 10:10:53 AM by Eric802]
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Davetrader
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Posted: 3/18/2013 10:21:33 AM
Google Hornady and click on their balistic calculator section. Input your MV and BC from the ammo you want to shoot and check the results. Match results to your abilities and set up.
Aeain
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Posted: 3/18/2013 11:06:23 AM
Originally Posted By jukeboxx13:
I would guess 500 yards since that is around the max range of 5.56.


National Match rifle competitions are shot with 5.56 out to 1000yards. I've seen effective kills with 5.56 out to 600 and the 6.8 when loaded to a Spec II load could easily do 600m. I'd say 700-800m is the ideal range. Beyond that it'd still be effective on target it you knew what you were doing.
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Posted: 3/18/2013 11:50:17 AM
I've made hits at 600 with my ACOG. No idea what kind of grouping or energy delivery there is out there, and my holdover was between the 6- and 800-yd BDC on my scope (5.56 calibrated) but they were hits on roughly a torso size object.
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Desert_AIP
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Posted: 3/18/2013 11:58:42 AM
Farther than the 5.56.
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Davetrader
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Posted: 3/18/2013 12:32:58 PM
[Last Edit: 3/18/2013 12:35:10 PM by Davetrader]
Originally Posted By Desert_AIP:
Farther than the 5.56.


Drop for SSA 140gr VLD load at 800 has 270 in of drop with a 100 yard zero.

Drop for Mk262 77gr SMk at the same range is 253 in of drop with a 2700 fps MV.

Pretty much the same

5.56 is still slightly flatter out 1000 yards as well.
Desert_AIP
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Posted: 3/18/2013 1:01:25 PM
Originally Posted By Davetrader:
Originally Posted By Desert_AIP:
Farther than the 5.56.


Drop for SSA 140gr VLD load at 800 has 270 in of drop with a 100 yard zero.

Drop for Mk262 77gr SMk at the same range is 253 in of drop with a 2700 fps MV.

Pretty much the same

5.56 is still slightly flatter out 1000 yards as well.


And a 110gr BTHP at 2650fps (from a 16" barrel) drops 270in at 800 yards.

But when speaking of effectiveness, you're talking terminal ballistics.

at 800
That 77gr SMK is at 1121fps and 215 ftlbs
The 110 BTHP is at 1103fps and 297ftlbs

Add 2" to the 6.8 barrel to equal the 5.56 and you add 50fps to the start of the equation, with over 300ftlbs remaining at 800.

An 85gr TSX is starting out at 3050fps from a 16" barrel.
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TaylorWSO
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Posted: 3/18/2013 1:57:29 PM

Originally Posted By ILoveMyAR:
What's the max range the 6.8 can handle with out to much trouble and not being effected by natural ellements much?

Out of say a 14.5 or 16" barrel!


Thanks
how much is "much"

1 SD, 50% of a specific parameter , what???

Kinda hard to answer an subjective question.

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Davetrader
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Posted: 3/18/2013 2:14:39 PM
[Last Edit: 3/18/2013 2:20:18 PM by Davetrader]
Originally Posted By Desert_AIP:

And a 110gr BTHP at 2650fps (from a 16" barrel) drops 270in at 800 yards.

But when speaking of effectiveness, you're talking terminal ballistics.

at 800
That 77gr SMK is at 1121fps and 215 ftlbs
The 110 BTHP is at 1103fps and 297ftlbs

Add 2" to the 6.8 barrel to equal the 5.56 and you add 50fps to the start of the equation, with over 300ftlbs remaining at 800.

An 85gr TSX is starting out at 3050fps from a 16" barrel.


I read Dr. Fackler's papers and can not remember an instance where ftlbs were an indicator of terminal effectiveness. Terminal damage comes from crush damage through expansion/fragmentation/ or yaw and tearing due to tissue stretch which is only significant in many tissues when the projectile is traveling over 2000fps. At these distances neither 5.56 or 6.8 is expanding or fragmenting so bullet diameter and yaw are what you get. Both traveling at 1100fps of there about. Sounds pretty much like 9mm ball ammo to me. A yawing 22cal or yawing 6.8cal. If someone had the actual dimensions you could compare the surface area of the two and see which does technically more damage. Is an increase in surface area likely to matter? Not really. Are we back to 9mm vs 40cal vs 45.

0-300 meters where you can get some nice expansion or fragmentation is a different story.


I forgot to add yaw characteristics. How early does each bullet yaw in tissue and how long does it travel sideways would also be a determining factor. All we need are some low velocity gel tests.



ILoveMyAR
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Posted: 3/18/2013 4:29:57 PM
Will do this! Thank you guys! I'm tryn to find a good longer range caliber for a new build so I just wanted to get an idea of the round first! If you guys have any other suggestions let me know.
bobweaver
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Posted: 3/18/2013 4:33:45 PM
Target only or hunting effectiveness?
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ILoveMyAR
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Posted: 3/18/2013 4:36:36 PM
Originally Posted By bobweaver:
Target only or hunting effectiveness?




Target only.
reelserious
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Posted: 3/18/2013 4:45:51 PM
Originally Posted By ILoveMyAR:
Will do this! Thank you guys! I'm tryn to find a good longer range caliber for a new build so I just wanted to get an idea of the round first! If you guys have any other suggestions let me know.




Long range 6.5 Grendal is what you want.
bobweaver
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Posted: 3/18/2013 4:56:26 PM
I'm not ballistics expert nor do I have extensive knowledge or time when it comes to distance shooting, however I have put a lot of rounds through my 68's; mostly into pigs and deer. I shoot SSA 85 TSX and 95 TTSX for pigs and SSA 110 PH's at deer. I limit my deer hunting to about 300 yards but I will take any shot I'm given at hogs but the furthest kill on a boar was pushing 500y or so. Past 500y it's pretty hard to judge the drop with my optics and the pigs I have hit at that range mostly make it to cover where I can't find them to be certain the shots were lethal.

I do have a 1000y range at my hunting lease where we've placed empty beer kegs at 100 yard intervals starting at 300 yards and the 68 will penetrate both sides of the keg out to 700 yards. After that, the rounds don't make it through both sides or just leave dents depending on where you hit it. I don't recall a 68 round ever penetrating the keg at 1000 yards, and the bullet drop is like 12-15ft. I also don't recall actually hitting the 1000y keg too often either. That's a difficult task even with a 3x12 and a 20" target crown barrel from H.
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Desert_AIP
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Posted: 3/18/2013 5:09:09 PM
[Last Edit: 3/18/2013 5:13:08 PM by Desert_AIP]
Originally Posted By Davetrader:

I read Dr. Fackler's papers and can not remember an instance where ftlbs were an indicator of terminal effectiveness...



I agree.

I was using that as simply illustrative since I don't think gelatin tests at 800 yards have been conducted for either round.

At that range neither projectile would perform as advertised because they are both too slow.
So of the two, with similar profiles and at relativey the same velocity, a heavier larger diameter bullet "should" have better terminal effects based on pure kinematics (larger wound channel, more momentum carries the projectile deeper into the target,etc. - although a larger diameter projectile will have more surface area and thus more drag/resistance as well, so the residual velocity will fall more quickly).

There is a difference between paper and flesh we speaking of "effectiveness".
But I certainly wouldn't be shooting either round at 800 yards hoping for very good terminal effects.

Either way I was attempting to point out (poorly) that selecting different projectiles for comparison needs some consideration.
The VLD seemed like an odd choice for comparison to me.
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Desert_AIP
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Posted: 3/19/2013 10:42:17 AM
Originally Posted By Davetrader:

I read Dr. Fackler's papers and can not remember an instance where ftlbs were an indicator of terminal effectiveness. Terminal damage comes from crush damage through expansion/fragmentation/ or yaw and tearing due to tissue stretch which is only significant in many tissues when the projectile is traveling over 2000fps. At these distances neither 5.56 or 6.8 is expanding or fragmenting so bullet diameter and yaw are what you get. Both traveling at 1100fps of there about. Sounds pretty much like 9mm ball ammo to me. A yawing 22cal or yawing 6.8cal. If someone had the actual dimensions you could compare the surface area of the two and see which does technically more damage. Is an increase in surface area likely to matter? Not really. Are we back to 9mm vs 40cal vs 45.





I was thinking about the part in red again last night.
I never made that connection before.

I get blinded by terms sometimes, thinking a bullet is "too slow" at range.
But, it's fascinating to me that at 800 yards these intermediate rifles perform (theortically) like a handgun at contact distance.
They still have the potential to be lethal.
Wow.

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Davetrader
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Posted: 3/19/2013 2:34:13 PM
Originally Posted By Desert_AIP:

Either way I was attempting to point out (poorly) that selecting different projectiles for comparison needs some consideration.
The VLD seemed like an odd choice for comparison to me.


I picked the VLD because I saw some write ups saying that would be the load to give the 6.8 some 6.5G long range performance. I was too lazy to run a bunch of different loads and see which one dropped the least. SSA did a pretty amazing job getting 2400fps in a 16" with a 140gr bbullet and still being mag length( in some mags).

I was being lazy.
Desert_AIP
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Posted: 3/19/2013 2:41:20 PM
I'm the king of lazy.
Why do you think I'm posting this at work?
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Lug1
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Posted: 3/19/2013 4:49:37 PM
[Last Edit: 3/19/2013 5:00:22 PM by Lug1]
Originally Posted By reelserious:
Originally Posted By ILoveMyAR:
Will do this! Thank you guys! I'm tryn to find a good longer range caliber for a new build so I just wanted to get an idea of the round first! If you guys have any other suggestions let me know.




Long range 6.5 Grendal is what you want.


Was scanning the thread just to find this quote. I knew there would be one even though OP specifically asked about 6.8. LOL This is the first one. I am guessing they will flow like a waterfall from here.
By the way I would like to go on record as saying a 6.5 Grendel or .264 LBC is a fine caliber. Not necessarily apples to apples when comparing to a 6.8 though. If you want to ring a gong at a 1000 yds it makes for a good cartridge.

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