Question about building an AR

[Atroxus]

I have read/heard that if you have an AR-15 lower that you can't put a .308 upper on it because the cartridges are too long so the magazines won't fit. But that you can use an AR-10 lower. My question is, if you get a multi-cal AR-10 lower can you use the smaller AR-15 cartridges and mags such as 5.56mm with the appropriate upper? Or in other words is it possible to use a single AR lower receiver for both 5.56 and .308?

[Swannytheswan]

easy answer is no if you want a .308 you need a ar-10 upper and lower if you want a .223/5.56 get a AR-15 upper and lower. there are some manufactures that make one that you can change but it is a different design than the conventional AR-15/AR10 design. See Colt http://www.coltsmfg.com/Catalog/ColtRifles/ColtLE90116S.aspx

[Swannytheswan]

or you could do a upper in 7.62x39 if you want a bigger pill

[Atroxus]

Nah, if it's not possible to build an AR that will do both 5.56 and .308 with the same lower, I will likely just build an AR-10 in .308 first. Then maybe somewhere down the road build an AR-15 in 5.56. I am kinda bummed though. That Colt looks pretty cool, but is likely waaay out of my price range.

[KFhunter]

1st question is to ask what you want it for - what is your end goal.

Once you know that it's just a matter of finding the tool to fit, that's the easy part.

[Swannytheswan]

1st question is to ask what you want it for - what is your end goal.

Once you know that it's just a matter of finding the tool to fit, that's the easy part.

I would agree there are a ton of options depending on  what you want

[MadHatter]

Nah, if it's not possible to build an AR that will do both 5.56 and .308 with the same lower, I will likely just build an AR-10 in .308 first. Then maybe somewhere down the road build an AR-15 in 5.56. I am kinda bummed though. That Colt looks pretty cool, but is likely waaay out of my price range.

I am just finishing up a long range 308 AR build.  If you have any questions PM me... There is a TON to learn, and the first thing to know is that they are NOT like an AR15 and everything fits everything.  In fact, there are times something made for your model of rifle won't even fit.  There is no industry standard, or MIL-SPEC, and I had it to do over again I wish I would have done a little more research in that department first.  Hell, even my gunsmith was blown away that a part made for a LR308 wasn't made for that particular receiver height style...

[Atroxus]

Nah, if it's not possible to build an AR that will do both 5.56 and .308 with the same lower, I will likely just build an AR-10 in .308 first. Then maybe somewhere down the road build an AR-15 in 5.56. I am kinda bummed though. That Colt looks pretty cool, but is likely waaay out of my price range.

I am just finishing up a long range 308 AR build.  If you have any questions PM me... There is a TON to learn, and the first thing to know is that they are NOT like an AR15 and everything fits everything.  In fact, there are times something made for your model of rifle won't even fit.  There is no industry standard, or MIL-SPEC, and I had it to do over again I wish I would have done a little more research in that department first.  Hell, even my gunsmith was blown away that a part made for a LR308 wasn't made for that particular receiver height style...

Yikes, so it sounds like maybe I would be better off cutting my teeth on a 5.56 build first.

Are there any calibers that would give similar performance to a .308 that could be run through a 5.56 lower? My goal is to have one lower that I can use with 5.56/.223 for target practice/varmint hunting, and swap another upper on it to use for deer, and maybe even elk some day.

[Jburke]

Nah, if it's not possible to build an AR that will do both 5.56 and .308 with the same lower, I will likely just build an AR-10 in .308 first. Then maybe somewhere down the road build an AR-15 in 5.56. I am kinda bummed though. That Colt looks pretty cool, but is likely waaay out of my price range.

I am just finishing up a long range 308 AR build.  If you have any questions PM me... There is a TON to learn, and the first thing to know is that they are NOT like an AR15 and everything fits everything.  In fact, there are times something made for your model of rifle won't even fit.  There is no industry standard, or MIL-SPEC, and I had it to do over again I wish I would have done a little more research in that department first.  Hell, even my gunsmith was blown away that a part made for a LR308 wasn't made for that particular receiver height style...

Yikes, so it sounds like maybe I would be better off cutting my teeth on a 5.56 build first.

Are there any calibers that would give similar performance to a .308 that could be run through a 5.56 lower? My goal is to have one lower that I can use with 5.56/.223 for target practice/varmint hunting, and swap another upper on it to use for deer, and maybe even elk some day.

This is exactly what I just finished.  I just finished an upper in 6.5 Grendel for hunting.  I have seen people use it for elk and bear, however I mainly intend on using it for deer.  I can't say where it ranks in comparison to the 308 though. 

[MadHatter]

Nah, if it's not possible to build an AR that will do both 5.56 and .308 with the same lower, I will likely just build an AR-10 in .308 first. Then maybe somewhere down the road build an AR-15 in 5.56. I am kinda bummed though. That Colt looks pretty cool, but is likely waaay out of my price range.

I am just finishing up a long range 308 AR build.  If you have any questions PM me... There is a TON to learn, and the first thing to know is that they are NOT like an AR15 and everything fits everything.  In fact, there are times something made for your model of rifle won't even fit.  There is no industry standard, or MIL-SPEC, and I had it to do over again I wish I would have done a little more research in that department first.  Hell, even my gunsmith was blown away that a part made for a LR308 wasn't made for that particular receiver height style...

Could do a 6.8...those use a standard ar upper... Just make sure you get a multi-cal upper...

A 308 ar is a blast to shoot... And if you start with the right platform it can go very easy for you... I just happened to get he wrong one to start with... But if you want to build one for accuracy, it's going to cost ya a good bit... I'll be honest I am in quite a bit of money right now for everything, and I'm not quite done yet... Going to CNC machine the handguard with some vents next for a little weight reduction.

I just got my barrel cut down to 20" from 24" and had it threaded for a suppressor. For the time being it's getting a JP Muzzle Brake through... Also got the stainless barrel moly coated, and had some accurizing stuff done. All in all it should take it from a 1.5moa gun to something more along the line of a 1/2moa or better... It's also got a Mk4 LR/T 6.5-20 in a 20 MOA leupold MK4 mount , Timney Trigger, magpul PRS stock, accushot monopod. And I started with a DPMS LR308.

Sent from my SAMSUNG-SGH-I747 using Tapatalk 2

[Atroxus]

Cool thanks for the input guys. I think I am going to start with a multi-caliber AR15 lower, build a 6.8spc upper to go on it first, then a 5.56/.223 upper later. Since the dimensions on 6.8spc are so close to 5.56, anyone know if I would be able to use the same magazines for both?

[Swannytheswan]

you can use the same magazine but most manufacture recommend not loading it full because it is a bigger diameter round and it will push out the sides, also needs a different bolt...if you went with .300 BLK uses the same size case as 5.56 so you could fill the mag and all you would need is a new barrel as it takes the same bolt as 5.56 but you sacrifice range....300blk is similar ballistics to a 30-30

[Swannytheswan]

just found this article that may be of interest http://www.thetruthaboutguns.com/2012/09/foghorn/ask-foghorn-6-8-spc-versus-300-blk/

[Atroxus]

just found this article that may be of interest http://www.thetruthaboutguns.com/2012/09/foghorn/ask-foghorn-6-8-spc-versus-300-blk/

Wow, thanks for the link. Sounds like .300BLK would be even better for me than the 6.8. I can't see myself taking a shot at any animal beyond 200 yards, and the areas I hunt I doubt I would even have many opportunities beyond 100 yards. Unless I misunderstood, it also seems that if I can't find .300BLK factory ammo, I could just trim down some 5.56 brass neck them down slightly and hand load them. (once primers/powder start becoming available again)

[Huntbear]

Heck.. look at the .300 OSSM.. need a new bolt and barrel, but has 30/06 ballistics.  Contact Chris Meyer with Titan Outdoors.. he loves his.

I shoot an AR in .243 WSSM...  I am pushing a 90 gr. Accubond faster than 3000 fps.   legal for deer, too..   and it rocks the yotes too.