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Old October 9, 2008, 12:22 AM   #1
Soldatlamour
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Newbie to AR-15 .... Additional Upper

Two weeks ago I picked up my first black rifle, a S&W MP15, in 5.56. I added an Eotech scope and have been to the range once. ^_^ That was a lot of fun.

Unfortunately, it did happen. I contracted the disease, and now I have the fever to get another AR. I want another caliber with some more "punch."

Here's my question: I was browsing through some sites and read a post that implied I could get a second upper in a different caliber (eg, 6.5 Grendel) and I'll be able to slap that on my lower (even though it's stamped "5.56").

Is that true ?

If it is, are there limits to what caliber of upper I can get to mate with my 5.56 lower?

As always, thanks for all your advices.
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Old October 9, 2008, 12:31 AM   #2
USMC88-93
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You are limited by the dimensions of the magazine well for instance .308 will not fit in the 5.56 mag well you would need an AR-10 style Lower for larger alternate calibers.

There are a number of alternate calibers that will function through the 5.56 lower given the appropriate magazines, bolt group and barreled upper.
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Old October 9, 2008, 12:31 AM   #3
IZinterrogator
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Quote:
Is that true ?
Yes, as long as the hole diameters are the same that mate the upper to the lower. This is not usually a problem.
Quote:
If it is, are there limits to what caliber of upper I can get to mate with my 5.56 lower?
Yes, the rounds have to be able to fit in a magazine that will fit in a 5.56mm lower. If you want to go with something bigger like 7.62mm, you need an AR-10 lower because it has a larger magazine well. 6.5mm Grendel and 6.8mm SPC uppers are popular options for the 5.56 lowers. I believe there was a thread recently where people were trying to name all of the calibers that would work with an AR-15 lower.
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Old October 9, 2008, 12:32 AM   #4
mbreitba
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There are definately limits - I have a DPMS AR-15, and I know that they offer a 204 ruger, a 6.8SPC, and a 7.62x39. You cannot grab a .308 upper and just slap it on there.

I'm sure there are several others that are available, but those are the three that I know should "drop in" on a AR-15 lower.
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Old October 9, 2008, 12:38 AM   #5
Soldatlamour
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I knew I could count on TFL guys/gals !

Wow, in about 10mins or so I have 3 very good responses. Thanks !

I'll search for that thread referencing what calibers are compatible in a ar15 lower to give me options for additional uppers.

New question: My magazines are 5.56/223. Will I need to get caliber-specific magazines, or will the 6.5 Grendel or other similar calibers rounds fit in my existing magazines ?
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Old October 9, 2008, 12:41 AM   #6
IZinterrogator
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Found the thread

http://thefiringline.com/forums/showthread.php?t=311636
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Old October 9, 2008, 12:44 AM   #7
IZinterrogator
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Will I need to get caliber-specific magazines, or will the 6.5 Grendel or other similar calibers rounds fit in my existing magazines ?
Depends on the round. The ribs on the 5.56 magazines sometimes impede function on other rounds, sometimes it's the follower that does it. I know you need specific mags for the 6.8mm SPC, not sure about the Grendel.
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"If ye love wealth better than liberty, the tranquility of servitude than the animated contest of freedom, go from us in peace. We ask not your counsels or arms. Crouch down and lick the hands which feed you. May your chains sit lightly upon you, and may posterity forget that you were our countrymen!” - Samuel Adams
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Old October 9, 2008, 12:53 AM   #8
Soldatlamour
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IZ - thanks for your advice

Any recommendations for on-line sites where I can order the new upper? Del-Ton, Bravo Company are two sites I'm reviewing.

again, thanks for your help
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Old October 9, 2008, 02:09 AM   #9
ChicagoTex
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Del-Ton, Bravo Company are two sites I'm reviewing.
And both are excellent sources.
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