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.

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[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.

[Atroxus]

Still thinking the.300blk sounds better. I really like the idea of being able to use the same bolt and magazines for 5.56.

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[Swannytheswan]

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.

with the .243 wssm does that fit in a AR-15 and what mags and bolt does it use?? sorry I don't want to hijack but I just read bout it and I like the sound of it

[Huntbear]

The .243,.25, and 300 OSSM all work very well on a standard AR platform..

I have Pmags that work just fine, I just took a small amount off the top, so the bigger/fatter case would go in...
I also have 3 metal 5 round mags for hunting.

It will take a new barrel in, and BCG.. I do not know for sure but I think there is only 2 companies making them.  The one I have is Olympic Arms. 

I can not wait to see how it performs on deer at 300-400 yards with the Accubond load I have worked up.  I also have a bunch of Varmint Grenades worked up for it too... basically will blow a yote in two...   

[KFhunter]

I've interested in the 6.5 grendal round myself

[JohnVH]

love my grendel

[FALFire]

Still thinking the.300blk sounds better. I really like the idea of being able to use the same bolt and magazines for 5.56.

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You will not get anywhere near .308 performance from a 300 Blackout. The 300BLK is the old 300/221 aka 300 Whisper from SSK Industries made long ago and works very well for very close range use when suppressed. There is a slightly better offering called the 7.62x40 that is available through Wilson Combat, Wilson was not the creator of the round but liked it so well he now offers it through his website. The 7.62x40mm is designed to shoot lighter weight .30 caliber bullets using a slower twist rate like 1-12 keeping velocities higher than the 300BLK. The 300BLK typically uses a 1-8 twist to spin the 200+ grain bullets.

I know full well what the 300BLK is, I have one and it isn't worth doing just because it uses the 5.56 bolt unless you plan on shooting suppressed, there are much better cartridges available and you already mentioned it.... the 6.8SPC. I've had two of those but sold them after having a very difficult time finding brass, perhaps brass is easier to acquire these days but not likely due to the recent events and the best brass comes from Silver State Armory located in Packwood, Wa.

If you are using the AR for big game the 243WSSM and 25WSSM flat out kick everything else in the teeth and never has to come up with a BS excuse for not performing. Now that Oly Arms has the .300 OSSM you can have near 30-06 performance from an AR15...That is serious firepower. The WSSM rounds feed exceptionally well from a slightly modified 20 round AR15 mag, the downside is you cannot build one from parts, there are only a couple of gunsmiths that have Olympic ARMS approval to build those uppers, Oly Arms of course then there is Mike Milli aka (DTECH) owner of Dedicated Technologies, he hangs out on Predator Masters.

Oly Arms will not sell you any of the parts nor will they sell to any gunsmith to build the WSSM calibers..... at least that was the way it used to be a few years ago.

There is one that you may have over looked, the 6WOA aka 6x6.8SPC aka 6mmDTECH, slight shoulder changes make them ever so slightly different and not interchangeable. They all use the 6.8SPC parent brass necked down to 6mm, using a 22" or longer 9 twist tube from BlackHole Weaponry located in Moses Lake, Wa. the 6x68 has produced some pretty nice results. I inquired about this wildcat round years ago when the 6.8SPC came about but then no one was doing anything with it, now it's the hottest ticket available and can easily shoot 95gr Bergers into one ragged hole at 100 yards. Recoil is slightly more than a standard 5.56 but velocities can be in the 22-250 zone, plus it is not as hard on the operating system as the WSSM rounds are and the brass is no where near as difficult to resize. I built a 6x6.8 upper for my neighbor and it's a shooter no doubt, first rounds loaded were producing 2 inch groups at 300 yards with noticeable velocities well above standard 6.8 rounds.

With the 6.8SPC we found we were losing too many coyotes when shooting them with 90gr Speer TNT'S even with good solid hits the dogs just ran off, so we moved to the 110 V-Max bullets where we started blowing huge holes in the pelts making them worthless, we dumped the 6.8's and went back to 22-250's then up to the 243Win using 95 Bergers, nice clean holes without the major pelt damage. The 6x68 will be used extensively next season for dogs as so far it has turned out to be a very good dog gun that is extremely accurate and easier on pelts using the Bergers.

One other 6mm caliber is the 6x45 which uses the standard 223 case necked to 6mm, this is what I use. It is very effective on coyotes with little to zero damage using Berger bullets and 55gr Nosler ballistic Tips. It is deer legal in this state and kills deer very well using most any 85gr soft point bullet. No mag mods need to be done and obviously still retains the 5.56 bolt.

[thinkingman]

Still thinking the.300blk sounds better. I really like the idea of being able to use the same bolt and magazines for 5.56.

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You will not get anywhere near .308 performance from a 300 Blackout. The 300BLK is the old 300/221 aka 300 Whisper from SSK Industries made long ago and works very well for very close range use when suppressed. There is a slightly better offering called the 7.62x40 that is available through Wilson Combat, Wilson was not the creator of the round but liked it so well he now offers it through his website. The 7.62x40mm is designed to shoot lighter weight .30 caliber bullets using a slower twist rate like 1-12 keeping velocities higher than the 300BLK. The 300BLK typically uses a 1-8 twist to spin the 200+ grain bullets.

I know full well what the 300BLK is, I have one and it isn't worth doing just because it uses the 5.56 bolt unless you plan on shooting suppressed, there are much better cartridges available and you already mentioned it.... the 6.8SPC. I've had two of those but sold them after having a very difficult time finding brass, perhaps brass is easier to acquire these days but not likely due to the recent events and the best brass comes from Silver State Armory located in Packwood, Wa.

If you are using the AR for big game the 243WSSM and 25WSSM flat out kick everything else in the teeth and never has to come up with a BS excuse for not performing. Now that Oly Arms has the .300 OSSM you can have near 30-06 performance from an AR15...That is serious firepower. The WSSM rounds feed exceptionally well from a slightly modified 20 round AR15 mag, the downside is you cannot build one from parts, there are only a couple of gunsmiths that have Olympic ARMS approval to build those uppers, Oly Arms of course then there is Mike Milli aka (DTECH) owner of Dedicated Technologies, he hangs out on Predator Masters.

Oly Arms will not sell you any of the parts nor will they sell to any gunsmith to build the WSSM calibers..... at least that was the way it used to be a few years ago.

There is one that you may have over looked, the 6WOA aka 6x6.8SPC aka 6mmDTECH, slight shoulder changes make them ever so slightly different and not interchangeable. They all use the 6.8SPC parent brass necked down to 6mm, using a 22" or longer 9 twist tube from BlackHole Weaponry located in Moses Lake, Wa. the 6x68 has produced some pretty nice results. I inquired about this wildcat round years ago when the 6.8SPC came about but then no one was doing anything with it, now it's the hottest ticket available and can easily shoot 95gr Bergers into one ragged hole at 100 yards. Recoil is slightly more than a standard 5.56 but velocities can be in the 22-250 zone, plus it is not as hard on the operating system as the WSSM rounds are and the brass is no where near as difficult to resize. I built a 6x6.8 upper for my neighbor and it's a shooter no doubt, first rounds loaded were producing 2 inch groups at 300 yards with noticeable velocities well above standard 6.8 rounds.

With the 6.8SPC we found we were losing too many coyotes when shooting them with 90gr Speer TNT'S even with good solid hits the dogs just ran off, so we moved to the 110 V-Max bullets where we started blowing huge holes in the pelts making them worthless, we dumped the 6.8's and went back to 22-250's then up to the 243Win using 95 Bergers, nice clean holes without the major pelt damage. The 6x68 will be used extensively next season for dogs as so far it has turned out to be a very good dog gun that is extremely accurate and easier on pelts using the Bergers.

One other 6mm caliber is the 6x45 which uses the standard 223 case necked to 6mm, this is what I use. It is very effective on coyotes with little to zero damage using Berger bullets and 55gr Nosler ballistic Tips. It is deer legal in this state and kills deer very well using most any 85gr soft point bullet. No mag mods need to be done and obviously still retains the 5.56 bolt.

This is where I'm heading.
If you reload, why mess with anything else.

[Swannytheswan]

i really need to start reloading so i can play with all those cool wildcats

[rock]

.450 bushmaster, go big or go home.

[JohnVH]

.450 bushmaster, go big or go home.

it wouldnt be that then, it would be the .50 beowolf

[mountainman]

To the first question of the Op...it can and has been done. Check out the multi-caliber Hydra. Quite a concept. Played with one quite extensively at thi years S.H.O.T. show. Can be put into .308 win in just a few seconds.. Check it out!...

http://www.mgi-military.com/index.php?id=2&sub_id=24

[Atroxus]

.450 bushmaster, go big or go home.

it wouldnt be that then, it would be the .50 beowolf

Can either of those be used with a standard ar-15 lower, and the 5.56 magazines?

To the first question of the Op...it can and has been done. Check out the multi-caliber Hydra. Quite a concept. Played with one quite extensively at thi years S.H.O.T. show. Can be put into .308 win in just a few seconds.. Check it out!...

http://www.mgi-military.com/index.php?id=2&sub_id=24

That Hydra system looks very cool, but I am guessing very expensive and all or mostly proprietary parts.

Part of the reason I am looking to build an AR instead of buying one whole is because I am on a very tight budget. Building will allow me to spread the cost out over time as I buy components. I'll be getting my lower and parts kit next month, and it will likely be a month or more after that till I have money to buy the next piece(s) for my build.

Budget concerns are also in part why I am still leaning towards the .300BLK. I like the idea of being able to swap just the barrel instead of an entire upper, as well as being able to use the same mags for both calibers. I also reload, so being able to cut down 5.56 brass to reload for .300BLK is very attractive as well.

[JohnVH]

.450 bushmaster, go big or go home.

it wouldnt be that then, it would be the .50 beowolf

Can either of those be used with a standard ar-15 lower, and the 5.56 magazines?

Yes, both are AR15 size

[rock]

Yep, same magazines and everything, just connect the new upper.

[Atroxus]

Yep, same magazines and everything, just connect the new upper.

Nice...guess I will have to do some more research/comparisons then.

[JohnVH]

I dont believe the same magazine part, unless you modify it is my guess. Id bet you have to buy AR15 mags made to fit the caliber you have, thats how my grendel is.

[rock]

450 bushmaster is common here in Indiana, as it's one of the few rifle rounds legal, most use the same magazine with little complications.

[CastleRocker]

My uppers take three completely different magazines, (or should I say, different follower, and some adjustments to the feed lips).   In addition to having different bolts.   

My DTech 25 WSSM is single stack due to the diameter of the case.  (Ultra Mag, or Winchester Short Mag, or WSSM...big bolt for a fat case!)

My 6.5 Grendel and my new 6mmAR (just a 6mm Grendel), take their own magazine and a smaller bolt.

The 17/223, the 20 Practical, 5.56/223, and the 300 Blackout take the stock one. 

[Atroxus]

The more research I do, the harder time I am having picking a caliber. Currently the front-runners are .300 BLK, .450 bushmaster, .458 SOCOM, and 6.8SPC.

Anyone near Marysville have an AR in any of these calibers that would be willing to take me shooting? Maybe some hands-on experience will help me decide.

[Jekemi]

I strongly encourage anyone that is planning on building an AR to go to www.ultimatereloaders.com and read Gavin's several part video on building the AR. He does both the .223 and the .308. In addition, if you want to build an AR that you don't have to register consider buying an 80% lower with no Serial # stamped on it. You have to purchase a corresponding jig and have access to a very good drill press or metal lathe but you can build an AR that Obama and his gun-hating friends know nothing about. It is perfectly legal.

[Atroxus]

Anyone know what is the max energy I could expect a .300BLK to generate at 200 yards, assuming 16" barrel, 150gr Barnes TTSX bullets, and keeping loads within SAAMI pressure specs?

I am kind of leaning towards .458 socom for the extra punch. It is sooo much more expensive for upper components and ammo, that if I can get 900+ ft/lbs of energy at 200 yards with a .300 blackout I will probably go that route though. I am not a marksman, at 200 yards I can maintain about a 5" group with my .30-06.(I am sure that in the right hands the rifle is capable of better) So I don't ever see myself shooting at a live animal at ranges farther than 200 yards.