My main quistion to build a lond range ar is what would be the best barrel length for it in either a 223 or 308.  (Not sure what im gunna do yet cause of the price dif in building)  But anything else anyone has to throw up here to help me or info would be greatly appreciated.

longer the better in terms of accuracy... and go .308

How far out are you trying to reach?  Im building an 18 inch and trying to reach out to 600 yds+.

Well im thinking maybe around a 20' barrel.  id like to be able to go to 800+ or so yds.  But at that im not sure who to look at for barrels.  Id love to go 308 to but it just costs more and i have a hard time finding stuff chambered in 308.  Could anyone hook me up with some good options in barrels in both 223 and 308,  also if i did 308 would i use the same gas block or are they specific for caliber?  Im new to building ar's so i could use some help.  I own a ar right now i bought (colt 6920) and i built a m40 a1 replica chambered in 7mm and now i want to do a semi auto long range.

I'm not saying that it's impossible,  but it's very improbable that you'll get a .223 out to 800 yards with consistency.  

My 20" barrel has made some 650 yard shots hitting a 18" gong,  but I had to really factor in some wind to shots like that.  Either way,  you'll want a few more inches on your barrel to hit out that far with an AR-15.

Have you thought about a 6.5 grendel, it can reach 800 yds with no problem?  I am currently debating building one with a 24 inch barrel.

A longer barrel will result in more velocity (and thus longer range), but a shorter barrel will flex less and give better accuracy within its useable range.  IMO, thicker is usually better than longer.

First of all, a 20" barrel in either caliber will be fine for most anything you mean to do with it.  Guys have been doing good work at 800m with 20" barrels and 175 grain M118LR for a long time now and with Mk262 you can reach out just as far, just with about 30% more windage.  Secondly, how far do you intend to shoot?

How about reloading?  It helps a lot if you're into rolling your own.  If not, you're limited to what's on the shelf at the store and that's not your best bet for LR ammunition, particularly in 5.56mm.  As an aside, additional barrel length has no positive effect on a rifle's accuracy and often does not impart as much velocity as many assume.

As far as making wind calls and everything im not really worried about that, and as for Range i dont see how 20" is that hard to reach that far with 5.56,  My Mk12 service rifle i took to afg only has a 18" barrel and 800yds is easy with that.  Its rated at 800yds max effect but iv gone and seen it go to about 950 with the right calls.  Im looking to maybe reach alittle farther than what i can with that rifle.  But i also dont wanna have it to rediculisly long.

Thanks for all the help so far,  Also what are some good names for barrels, anyone make a bull barrel for the ar?

It seems we've carried some of the same stuff.  

FWIW, I shoot to 1K yards (and a little farther here and there) with a 20" Krieger barrel and 77 grain Match Kings. I use TAC for a load that runs a bit over 2800 fps in that 20".  It's very close to Mk262 in the 18" and gets to 1K with 10.3 mils at 70F/23.79" Hg.

As for brands, I'm a Krieger fan.  I'm sure any of the high-end names will be fine, but I'm only doing Krieger at this point.

A 20 inch .223 is good to 1000 yards easily with good 77 gr SMK loads.

Sheesh!  We've shot a 12.5" SBR with an ACOG out to 800 yards.  700 reliably... but 800 we were able to get some hits.

Someone posted some interesting data awhile back showing the differences in velocities.
Halfway down the page

For a good price BravoCompany has heavy profile 18" and 20" SS barrels.
I'm no expert by any means but just thought I'd share some things I have come across

I have one of the Rainier Ultra Match barrels and its a laser with solid .223 rds, but I haven't gone out to 800+ yds yet. Maybe someone else can chime in on that.

Range time.  Practice, practice, practice.  Youtube long range AR's.  It will give you a visual of what these guys are doing to reach those types of distances.

Just finished a build with a BCM 20" heavy barrel in 223 and have been really happy out to 400 yards.  I will say it turned out to be one of the heaviest rifles I have ever held but with a muzzle brake it has virtually no kick and barely budges when fired.  

Marc

I have shot my spr build to 730 yards with 77g Sierra match kings out of my white oak 18'' spr barrel.  Wind was only about 5mph so it was not a huge factor.

I see this a lot, but I seldom see anyone saying what to practice.  

Just don't go off thinking it's about round count.  It isn't.  You're not trying to be a ranked pistol shooter and you have to develop so-called "muscle memory" in a more deliberate way.  The important things are 1) fundamentals of marksmanship, from body position to follow through, 2) knowing your elevation data and 3) reading wind speed, direction and value.  Once you work out the fundamentals well enough to shoot tight groups at 100 yards, you need to move to elevation data (super easy) and windage (not easy).  Once those items are working reasonably well you can get the job done just fine with a proper 5.56x45mm load.  Again, you need to pay attention to what each shot teaches you about all of these factors, which requires relatively few rounds fired, but takes a huge amount of attention to detail and honesty.

In terms of equipment, all you need is a good barrel, decent glass, proper ammunition and a good trigger to top things off.

Im not worried about range time.  or starting small for muscle memory.  Im in the USMC and am plenty good with a AR.  Like i said i carried a Mk12 around afghanistan for 7 months and my issued rifles are a M4A3 and Mk12, I have had plenty of trigger time behind AR varients.  For those that dont know the Mk12 is a 5.56 DMR in the Marine Corps and Im a so called "Pig" to speak so iv gone through the Marine Corps "basic" sniper course.  Im looking for pointers on the build, as far as barrels, trigger assemblies, gas systems and so on.  Thanks for the help so far. And for another question im wondering what kinda distances i could look to hit with the Kreiger Varmatch 26" barrel.  It looks like a thicker (bull) fluted barrel and im looking to take it to the range and plink for hours.  But at the same time id like to be able to mount a suppressor so im just not sure how to go... any help greatly appreciated

I have shot 223 in Hi Power to 600 yards quite a bit with a 20" rifle. IF I wanted to go longer I would consider a 24 or 26" barrel.

I have shot 308 to 1000 with a 24, and 26 inch barrels with 175 and 185gr bullets.

An 18" barreled 308 with 168 or 175gr bullets will go to 850 yards, no problems.

If you want a lightweight 850 yard 308 AR, take a look at the Christensen Arms CA-10. The 18" rifle weighs 7.3lbs...

They will build you one with a longer barrel as well...

My post really wasn't for you, but a lot of folks were chiming in and I thought certain points should be covered where possible.

For barrels, names such as Krieger, Bartlein, Shilen, Noveske, Douglas and the like will be fine.  There are others that will work, too.  Barrel thickness is neither here not there, generally speaking, though a heavier rifle is a bit easier to shoot well, not to mention that heavier barrels heat up more slowly, though this shouldn't be a huge issue with a quality barrel, as the POI shouldn't walk from the cold bore to the last shot fired, anyway.  Added rigidity may help, or it may not, but I don't buy into the whole fluting thing. There's just not enough hard data to support it and plenty of anecdotes and (professional) opinions to indicate that it may be pointless and potentially harmful.  A standard rifle length gas system is fine for the 18-20" barrels, though I know longer systems have been used with longer barrels.  

I have a few Geissele 2-stage triggers and one Jewell.  They're all very nice, adjustable triggers and work as well as or better than the KAC units with which you are familiar.  I would go with these, especially the Geissele, before I would go with some more generic 2-stage.

Regarding barrel length, I suggest a 20" version.  IME (and according to some published numbers), anything longer than 18" is creeping past the point of diminishing returns in terms of velocity gained per inch.  Even for published load data the 20" is running very close to the 24" test barrels.  IMHO, there's no need to go longer than 20" to get to 1000 yards with 77 grain pills in 5.56x45mm.  This is especially true if you're considering a suppressor.  My 20" Krieger with TREK-T is still a pretty handy rifle for what it is, though another 4-6" would make it uncomfortably long for me.  We get into that in this thread on powder selection for 77 grain SMKs HERE.

Any barrel from a top barrel maker will be ok, with an AR I think the barrel is the most important variable as far as accuracy is concerned and I'd get a 1/7 barrel...minimum 1/8 shooting 77's or 80's.

read this article

link

Barrel: WOA
Trigger: Geissele
Gas: Rifle
Length 18"

Hard to argue with this.  

add... FF rail of your choice, SMK handloaded 77s, and the rest is history.

Do you have an recommendations on where to get this kind of training/knowledge? I don't come from a military background, but have always been interested.

Since you are in OK, Badlands might be a great start.  It's not far from Lawton.  I've worked with some of their precision rifle staff in outside venues and based on that I can certainly recommend their courses.

Other possibilities are Accuracy1st just down in TX (I've done a two week course with Todd Hodnett and the training is excellent), Rifles Only in south TX (more focus on fundamentals/marksmanship) and GPS Defense in AZ (more fieldcraft than Rifles Only).

Some private ranges also host instructors, so check those out, too.

Length doesn't determine accuracy, just velocity.

+1 for the 6.5

Thats what she said.

True, but how effective is that 77 gr bullet going to be when it finally arrives?

It's not going to knock over a popper but it'll create tension pneumothorax or an infected wound easily enough. Kind of like 7.62 at 800 yards.

Oh good you're here.

Shot is shot, as the guys who've done it like to say.

Effective enough to make a hole in the target or ring the metal which is all the OP needs

Thanks!

Longer is better!