upper and lower questions

chunick · 04-12-2008, 05:21 PM

My question is, I have a Bushmaster chambered in a .223, and was curious if a Rock River upper in a 6.8 upper would work? And if so, would i need to change bolt, trigger or whatever? Or if any and all upper from any manufacture would work in with any or all lowers? Any info would be great. Thanks in advance.

Pred · 04-12-2008, 06:28 PM

Yes, it will work. As far as I know you'll need a new bolt carrier group(should come with the upper anyways). But the trigger/hammer should be fine. I don't know about the mags though. I know standard mags will work with a lot of rounds, only they will be single stack instead of double stack. Again, I've not done much research on this so maybe someone will jump in and tell me if I'm wrong.

at4rxj · 04-12-2008, 10:06 PM

It's actually the same carrier. All you technically need is the barrel, bolt, and magazine.

However, I'm assuming you want a different upper completely to swap out? If so, just order a complete upper receiver so you don't have to mess with swapping the bolts around. Then you have a .223/5.56 bcg and a 6.8 bcg...

Make sure you keep your mags separate too.

Pred · 04-12-2008, 10:35 PM

Won't the standard AR mags hold the 6.8 round? I know the .458 SOCOM will work, as will the 7.62x39. However I think with the SOCOM a 30 round mag will hold 10 rounds, and with the Russian round it will hold 7 rounds.

Uncle Red · 04-13-2008, 01:48 AM

I've been told you have to change the buffer too. Check to make sure.

-UR

chunick · 04-14-2008, 09:57 AM

Why would i need to change the buffer? Thank you guys for your imput, I apprieciate it very much.

Beer Forever · 04-14-2008, 12:31 PM

As far as I know, it is the bolt, barrel, and magazine that are different. A lot of guys have many different uppers in different calibers and just use the one lower. If you have a complete RRA upper in 6.8, you can toss it on your complete lower with a 6.8 magazine and you are ready.

Pred · 04-14-2008, 12:41 PM

I'm still waiting for someone to say that a normal AR magazine won't work for the 6.8. I realize a 30 round mag won't hold 30 rounds of 6.8, but for some reason I still think it will work.

at4rxj · 04-14-2008, 03:11 PM

the normal 5.56 mag won't work

It's something with the size of the round itself. The position, and it believe it's just the height, of where the two rounds need to sit is different. A 6.8 in a 5.56 mag will sit too high, and the 5.56 in a 6.8 mag will sit too low. I know that the 6.8 won't work in the 5.56 pmag because the round is wider and causes the sides to bulge... or at least that's what I read.

It's a different follower as well.

Also, you can use the same buffer. In fact, Ko-Tonics (a big 6.8 barrel maker) RECOMMENDS a standard buffer instead of a heavy one. Some of the Hornady ammo won't reliably cycle an ar with the heavy buffer.

Just get a complete 6.8 upper (incl bolt carrier group), and a couple of mags, and you're in business.

Darkfront · 04-14-2008, 04:21 PM

The 5.56 mag won't work from what I've heard because the curvature of the feed lips is all wrong for the diameter of the 6.8. People have modified their 5.56 mags to work, but that's just one more thing that may or may not affect the reliability of that mag for both calibers. Better off just buying 6.8 mags.

chunick · 04-14-2008, 10:59 PM

I really appreciate all of the imput guys, it has all been really big help.

04-12-2008, 05:21 PM	#1
chunick Registered User Join Date: Apr 2008 Location: Salt Lake City, Utah Posts: 3 Trader Rating: (0)	upper and lower questions My question is, I have a Bushmaster chambered in a .223, and was curious if a Rock River upper in a 6.8 upper would work? And if so, would i need to change bolt, trigger or whatever? Or if any and all upper from any manufacture would work in with any or all lowers? Any info would be great. Thanks in advance.

04-12-2008, 10:06 PM	#3
at4rxj Senior Member Join Date: Oct 2005 Location: Houston, TX Posts: 802 Trader Rating: (0)	It's actually the same carrier. All you technically need is the barrel, bolt, and magazine. However, I'm assuming you want a different upper completely to swap out? If so, just order a complete upper receiver so you don't have to mess with swapping the bolts around. Then you have a .223/5.56 bcg and a 6.8 bcg... Make sure you keep your mags separate too. __________________ modulARweapons.com

04-13-2008, 01:48 AM	#5
Uncle Red Senior Member Join Date: Mar 2002 Location: Indiana Posts: 547 Trader Rating: (0)	I've been told you have to change the buffer too. Check to make sure. -UR __________________ "A well regulated militia, being necessary to the security of a free State, the right of the people to keep and bear arms, shall not be infringed"--Amendment II, Bill of Rights "He that would make his own liberty secure must guard even his enemy from oppression; for if he violates this duty he establishes a precedent that will reach to himself."--Thomas Paine "He that hath no sword, let him sell his garment and buy one." - Jesus, Luke 22:36

04-14-2008, 12:31 PM	#7
Beer Forever Senior Member Join Date: Dec 2005 Location: Tucson, AZ Posts: 2,694 Trader Rating: (0)	As far as I know, it is the bolt, barrel, and magazine that are different. A lot of guys have many different uppers in different calibers and just use the one lower. If you have a complete RRA upper in 6.8, you can toss it on your complete lower with a 6.8 magazine and you are ready. __________________ Paramedic sks forever

04-14-2008, 03:11 PM	#9
at4rxj Senior Member Join Date: Oct 2005 Location: Houston, TX Posts: 802 Trader Rating: (0)	the normal 5.56 mag won't work It's something with the size of the round itself. The position, and it believe it's just the height, of where the two rounds need to sit is different. A 6.8 in a 5.56 mag will sit too high, and the 5.56 in a 6.8 mag will sit too low. I know that the 6.8 won't work in the 5.56 pmag because the round is wider and causes the sides to bulge... or at least that's what I read. It's a different follower as well. Also, you can use the same buffer. In fact, Ko-Tonics (a big 6.8 barrel maker) RECOMMENDS a standard buffer instead of a heavy one. Some of the Hornady ammo won't reliably cycle an ar with the heavy buffer. Just get a complete 6.8 upper (incl bolt carrier group), and a couple of mags, and you're in business. __________________ modulARweapons.com Last edited by at4rxj; 04-14-2008 at 03:31 PM.

04-12-2008, 06:28 PM	#2
Pred Banned Join Date: Aug 2005 Location: Kentucky Posts: 3,873 Trader Rating: (0)	Yes, it will work. As far as I know you'll need a new bolt carrier group(should come with the upper anyways). But the trigger/hammer should be fine. I don't know about the mags though. I know standard mags will work with a lot of rounds, only they will be single stack instead of double stack. Again, I've not done much research on this so maybe someone will jump in and tell me if I'm wrong.

04-12-2008, 10:35 PM	#4
Pred Banned Join Date: Aug 2005 Location: Kentucky Posts: 3,873 Trader Rating: (0)	Won't the standard AR mags hold the 6.8 round? I know the .458 SOCOM will work, as will the 7.62x39. However I think with the SOCOM a 30 round mag will hold 10 rounds, and with the Russian round it will hold 7 rounds.

04-14-2008, 09:57 AM	#6
chunick Registered User Join Date: Apr 2008 Location: Salt Lake City, Utah Posts: 3 Trader Rating: (0)	Why would i need to change the buffer? Thank you guys for your imput, I apprieciate it very much.

04-14-2008, 12:41 PM	#8
Pred Banned Join Date: Aug 2005 Location: Kentucky Posts: 3,873 Trader Rating: (0)	I'm still waiting for someone to say that a normal AR magazine won't work for the 6.8. I realize a 30 round mag won't hold 30 rounds of 6.8, but for some reason I still think it will work.

04-14-2008, 04:21 PM	#10
Darkfront Senior Member Join Date: Nov 2007 Posts: 106 Trader Rating: (0)	The 5.56 mag won't work from what I've heard because the curvature of the feed lips is all wrong for the diameter of the 6.8. People have modified their 5.56 mags to work, but that's just one more thing that may or may not affect the reliability of that mag for both calibers. Better off just buying 6.8 mags.

04-14-2008, 10:59 PM	#11
chunick Registered User Join Date: Apr 2008 Location: Salt Lake City, Utah Posts: 3 Trader Rating: (0)	I really appreciate all of the imput guys, it has all been really big help.