[sharpshooter33]

I recently emailed LMT ref a 6.8 enhanced bolt and enhanced F/A carrier.
They told me that the 6.8 would not function with a enhanced F/A carrier?

I like the extra weight of the F/A carriers. I find that the extra time locked is better for accuracy in 5.56 and is easier on my brass. I was wondering if there is a reason they would say their enhanced carrier would not function for 6.8?

2nd question has anyone shot a 16" barrel out to 600yards? I am wanting to build a carbine size 6.8 that I can still shoot 600yards without too much bullet drop.

Thanks
SS33

 

[constructor]

I recently emailed LMT ref a 6.8 enhanced bolt and enhanced F/A carrier.
They told me that the 6.8 would not function with a enhanced F/A carrier?

I like the extra weight of the F/A carriers. I find that the extra time locked is better for accuracy in 5.56 and is easier on my brass. I was wondering if there is a reason they would say their enhanced carrier would not function for 6.8?
The 6.8 does use faster powders so if a .223 slows to FA carriers and H2 buffers then it would effect the 6.8 more.
With light bullets, fast powders and a longer than mid length gas system it could cause short stroking in the 6.8.
2nd question has anyone shot a 16" barrel out to 600yards? I am wanting to build a carbine size 6.8 that I can still shoot 600yards without too much bullet drop.I have shot an 18" out to 800yds does that count?

Thanks
SS33

 

[sharpshooter33]

I recently emailed LMT ref a 6.8 enhanced bolt and enhanced F/A carrier.
They told me that the 6.8 would not function with a enhanced F/A carrier?

I like the extra weight of the F/A carriers. I find that the extra time locked is better for accuracy in 5.56 and is easier on my brass. I was wondering if there is a reason they would say their enhanced carrier would not function for 6.8?
The 6.8 does use faster powders so if a .223 slows to FA carriers and H2 buffers then it would effect the 6.8 more.
With light bullets, fast powders and a longer than mid length gas system it could cause short stroking in the 6.8.
2nd question has anyone shot a 16" barrel out to 600yards? I am wanting to build a carbine size 6.8 that I can still shoot 600yards without too much bullet drop.I have shot an 18" out to 800yds does that count?

Thanks
SS33

How much drop did you have and what grain bullets were you using? I was trying to stay with the 16" length on my build. Going with an 18" was a possibility, but I kinda wanted to save the 2" in turn radius. Yea I know not much of a difference, but I figure I'm only building one 6.8 so I want it to fit most of my needs. I'm not sure I'm following you on the gas system though. If they leave the barrel at similar speed and pressure other than the powder speed. I don't understand lighter bullet? I'm missing something. /color]

 

[marinesg1012]

The 6.8 has a different pressure curve then the 556, that is also why it is less effected by the shorter barrels then the 556. I would start with a standard buffer with the tubbs spring and see how it goes from there.

the 18 gives you a little more FPS then the 16 but i still think the 16 is best all around.

 

[kamojo]

The 6.8 has a different pressure curve then the 556, that is also why it is less effected by the shorter barrels then the 556. I would start with a standard buffer with the tubbs spring and see how it goes from there.

the 18 gives you a little more FPS then the 16 but i still think the 16 is best all around.

+1 :wink:

 

[borderpatrol]

The 6.8SPC is not a 600 yard cartridge. It can "shoot" that far, but it's designed for 300 yards or less while increasing terminal performance in a AR based rifle. Hornady's 100 grain V-max has a B.C. almost identical to a .224 77 grain Sierra Match King and only 100 fps less velocity than the .223. It would work OK provided your getting the accuracy (minute of angle or less) from your gun. I've noticed lots of loads group 1" or less at 100 yards with a 6.8 but open up considerably at longer ranges. Most of my 100 yard 1" loads are 5" at 200. Not bad, but not match grade. I have not put enough loads together to to make any universal statements. This has been my experience so far. This type of accuracy is also typical of most rack grade AR15's.

With a premium barrels and better bullets I'm sure improvements will come. A B.C. of .450 or better will work well to 600 yards with as little as 2500 fps. I think this is possible without going to VLD's.

 

[constructor]

I recently emailed LMT ref a 6.8 enhanced bolt and enhanced F/A carrier.
They told me that the 6.8 would not function with a enhanced F/A carrier?

I like the extra weight of the F/A carriers. I find that the extra time locked is better for accuracy in 5.56 and is easier on my brass. I was wondering if there is a reason they would say their enhanced carrier would not function for 6.8?
The 6.8 does use faster powders so if a .223 slows to FA carriers and H2 buffers then it would effect the 6.8 more.
With light bullets, fast powders and a longer than mid length gas system it could cause short stroking in the 6.8.
2nd question has anyone shot a 16" barrel out to 600yards? I am wanting to build a carbine size 6.8 that I can still shoot 600yards without too much bullet drop.I have shot an 18" out to 800yds does that count?

Thanks
SS33

How much drop did you have and what grain bullets were you using? I was trying to stay with the 16" length on my build. Going with an 18" was a possibility, but I kinda wanted to save the 2" in turn radius. Yea I know not much of a difference, but I figure I'm only building one 6.8 so I want it to fit most of my needs. I'm not sure I'm following you on the gas system though. If they leave the barrel at similar speed and pressure other than the powder speed. I don't understand lighter bullet? I'm missing something. /color]

I Z my rifles at 300 yds, the comeup was around 20 MOA at 800 yds with a 120 Barnes Solid with a BC of .411 going about 2680. I think I would use the Nosler accubond now it has a BC of .410 and I can push it to 2650 or 2700 with a 16" barrel and stiff handloads(30.8gr of 10X careful it's hot and compressed ). The 16" should only lose 50 fps to the 18" so that not a big deal.
Adam is right about the pressure curve, I believe most ARs open the bolt with apx 14000 psi, the 6.8 pressure drops off faster because of faster powders and a larger bore area to fill. When I said a FA carrier could cause short stroking I should have explained. They are more than likely using poor factory ammo with a heavier carrrier and their high performance springs they may have experienced short stroking. If you handload for performance like I do short stroking isn't an issue unless you are using 80-90 gr bullets with 4198 or faster powders. If you like 16 carriers I would try it, if it doesn't work you can always find a home for it in another rifle

 

[sharpshooter33]

Thanks guys! That's the type of info I'm looking for. Is the Tubb Spring stronger or weaker than a standard spring? Or just more consistent?
The 5.56 wasn't really a 600 or 1000 yard round either But it's become one.
I've found that same thing with 100yrd vs 600yr bullets. I love my 55gr Sierra GK in 5.56 for 100yrds, but they tend to float around out at 600yrds. That's one thing that has concerned me so far about bullet choices in .277
I was going to get a barrel made by CLE (match quality) but they don't do the SPCII cut. PacNor is a 2nd choice. I want a good quality match barrel. Does anyone have another barrel maker?

The 600yrd limit for me is because the range I shoot only goes to 600 and realistically I'm getting older and it's about my max effective range anymore. :|
Thanks for all the input guys!!!
:shock:

The 6.8SPC is not a 600 yard cartridge. It can "shoot" that far, but it's designed for 300 yards or less while increasing terminal performance in a AR based rifle. Hornady's 100 grain V-max has a B.C. almost identical to a .224 77 grain Sierra Match King and only 100 fps less velocity than the .223. It would work OK provided your getting the accuracy (minute of angle or less) from your gun. I've noticed lots of loads group 1" or less at 100 yards with a 6.8 but open up considerably at longer ranges. Most of my 100 yard 1" loads are 5" at 200. Not bad, but not match grade. I have not put enough loads together to to make any universal statements. This has been my experience so far. This type of accuracy is also typical of most rack grade AR15's.

With a premium barrels and better bullets I'm sure improvements will come. A B.C. of .450 or better will work well to 600 yards with as little as 2500 fps. I think this is possible without going to VLD's.

 

[ron169]

here is a thread from December of good ole 2007, and just think of the advancements that have been made with the 6.8 since then. Its a report on different uppers that they tested out to 650 yards
http://www.ar15.com/forums/topic.html?b=3&f=12&t=353523

Here is the final result sheet, notice the MSTN with a 16 in barrel held sub MOA at 650 yards, and the Noveske wasnt to far behind either. With what we know about chamber, twist, better bullets, and a longer barrel, im sure you could easily improve on a 5.5 inch group at 600 yards!

 

[-k-]

It is not the Auto carrier, it is the Enhanced carrier that could be a problem.

 

[Test_User]

K is correct. They are talking about their enhanced carrier which vents the gases from the carrier much faster and is to be used specially for barrels that have to much duration or barrel length past the gas port. This is not needed for the 6.8 at all. FA carriers work great with the 6.8 and is all I use. You can even add more weight. It is no different then adding weight to the buffer. They were assuming you meant the enhanced as that is the question they would usually get asking about carriers.

The ONLY 6.8 BOLT they sell is the Enhanced version and is quite good but very $$$$. Someone should make one even better and for a fair price. :idea:




Whatever bolt it can be mated to a AR-15 or M16 otherwise known as semi or F/A carriers but not the LMT enhanced carrier. As LMT does not really cater to the end user their website is not as technical hand holding as typical commercial sites.

As to the range the 6.8 is suppose to work at; 300 yards. Those were the original guidelines and needs / reasons for making the round it is not restricted by them just that it must meet them. It also stated that it had to be able to be used out to 500 but that was not its main range. The 6.8 is more then capable of shooting out to 600 and past. It has less drop then many other round known for that range out to 600 including the 308 and 6.5 and 5.56.

 

[ron169]

So would the enhanced carrier come in handy for someone shooting a suppressed AR-6.8 Tim? Seems like they are over gassed from what I remember, so would the bleed off be an advantage, or just screw you up in you take the supressor off?

 

[Test_User]

Screw you up for sure, much better to have an adj gas block.

 

[ron169]

Well ill add that to the good to know list.... now when are you gonna start selling to 10-12 in barrels and build me a SBR with Adj gas block? Huh? You know there is a market for 10-12 in and 18 inch barrels that yall havent tapped!

 

[Test_User]

Yes there is but its roughly 100:1 all combined 16" versus every other length.

 

[BLACK LION]

CONSTRUCTOR ^^^^^^ can get you the barrel you need .... it will be the optimal 6.8spc specs

 

[tbones54]

I have a question for the Gurus. I recently bought a Model 1 6.8 upper which is I assume 1-9.5 twist. From what I have read most dont recomend this twist rate. Bottom line ,is this twist safe to shot with commercial loads or not. thanks

 

[ron169]

Well its the twist rate combined with the SAAMI chamber. I would think you are good to go with standard SSA commercial loads, as well as hornady ammo, but I would seriously be looking into a new barrel, or at the very least reaming the chamber to a SPC II

 

[Test_User]

Reaming the chamber to DMR would be my first suggestion then if you are not happy with the accuracy if a say you can not get anything near 1-1.5 moa with a good scope and loads then look for a new barrel. The Xtreme barrel or the ARperfomance Lothar barrels have ideal specs and offer different two levels of barrel to choose from.