Are AR-15 Parts Interchangeable?

Code A · July 5, 2008, 01:14 PM

Hello,

I own a Colt .223, model MT6700 Match 20" Target Comp HBAR. It's a great rifle for many purposes. However, I would like to have the option of a more compact, close quarters rifle with a collapsable buttstock and a shorter barrel.

Can I buy any brand of upper receiver and swap out the stock upper receiver? Is it that simple? If I do this are there potential problems? Is it as simple as pulling out the pin and replacing it with a new Upper, or gunsmithing involved?

Thanks,
Code A

wjkuleck · July 5, 2008, 02:13 PM

Any quality upper can be installed on your lower.

Check your takedown (rear) and pivot (front) pins. If they are the same size, you're good to go as-is. If the front (pivot) pin is larger in diameter, you'll need a "offset" pin, which will be a five or six dollar investment. The "standard" upper/lower "interface" has both pins at .250". Colt used a larger front (pivot) pin/pin hole to make installation of M16 uppers impractical. As noted above, it's easy to get around that "limitation."

Regards,

Walt

MeekAndMild · July 5, 2008, 06:03 PM

Quote:

Can I buy any brand of upper receiver and swap out the stock upper receiver?

There is a problem here, from all I've read on the internet about the matter. There are pistol uppers on the market as well as short machine gun uppers, both of which do not have barrels of sufficient length to legally possess unless you've already got the paperwork and tax stamp for a NFA machine gun, a NFA short barreled rifle or a pistol. Having a short barreled upper without one of these lowers to put it on may be considered "intent to make" and result in a hefty fine and jail sentence. Bottom line, if its sold as a rifle then get an upper with a sufficiently long barrel to be a legal rifle. (I'm not a lawyer nor a BATFE agent so this is just what I've read and may not be accurate. Check with your local BATFE office before buying and they will probably be able to give you the straight skinny about it.)

globemaster3 · July 5, 2008, 11:17 PM

+1 on Walt's inputs. That's the beauty of the AR. So many uppers, so little $. And if you want to look at other calibers, you can get into anything that is about the same OAL as the 5.56. Some popular ones are 6.5 Grendel, 6.8 Rem SPC, .458 SOCOM, .50 Beowolf. There are others out there, this is just the tip of the iceberg. If you go this route, realize you will also need another bolt, carrier, and mag.

If you look online at DPMS, Olyimpic Arms, Bushmaster, or any other AR manufactuer, almost all sell just the upper. Also look at Model 1 Sales and M & A. Read the fine print, though. Most do NOT include a bolt carrier assembly and charge from $100 on up for that alone. The options are almost endless.

In terms of the short barrel concern, 16" barrels and up will keep you out of the SBR zone.

Good luck!

July 5, 2008, 01:14 PM	#1
Code A Junior Member Join Date: July 2, 2008 Location: Ohio Posts: 3	Are AR-15 Parts Interchangeable? Hello, I own a Colt .223, model MT6700 Match 20" Target Comp HBAR. It's a great rifle for many purposes. However, I would like to have the option of a more compact, close quarters rifle with a collapsable buttstock and a shorter barrel. Can I buy any brand of upper receiver and swap out the stock upper receiver? Is it that simple? If I do this are there potential problems? Is it as simple as pulling out the pin and replacing it with a new Upper, or gunsmithing involved? Thanks, Code A

July 5, 2008, 02:13 PM	#2
wjkuleck Senior Member Join Date: March 13, 2007 Location: Ohio, USA Posts: 1,220	Any quality upper can be installed on your lower. Check your takedown (rear) and pivot (front) pins. If they are the same size, you're good to go as-is. If the front (pivot) pin is larger in diameter, you'll need a "offset" pin, which will be a five or six dollar investment. The "standard" upper/lower "interface" has both pins at .250". Colt used a larger front (pivot) pin/pin hole to make installation of M16 uppers impractical. As noted above, it's easy to get around that "limitation." Regards, Walt __________________ Author, NEW! The M1911 Complete Owner's Guide The M14 and M1 Garand Complete Assembly Guides The M1 Garand Complete Assembly Guide The AR-15 Complete Assembly and (New 4th Edition) Owner's Guides

July 5, 2008, 11:17 PM	#4
globemaster3 Senior Member Join Date: January 28, 2006 Posts: 1,482	+1 on Walt's inputs. That's the beauty of the AR. So many uppers, so little $. And if you want to look at other calibers, you can get into anything that is about the same OAL as the 5.56. Some popular ones are 6.5 Grendel, 6.8 Rem SPC, .458 SOCOM, .50 Beowolf. There are others out there, this is just the tip of the iceberg. If you go this route, realize you will also need another bolt, carrier, and mag. If you look online at DPMS, Olyimpic Arms, Bushmaster, or any other AR manufactuer, almost all sell just the upper. Also look at Model 1 Sales and M & A. Read the fine print, though. Most do NOT include a bolt carrier assembly and charge from $100 on up for that alone. The options are almost endless. In terms of the short barrel concern, 16" barrels and up will keep you out of the SBR zone. Good luck!