I was talking with a fellow shooter about all the different calibers available for the AR &  how I was looking forward to getting a 2nd upper in another caliber.  He said since my lower was marked .223-5.56mm, I could only shoot .223-5.56mm.
I find that hard to believe considering how popular and widely available the other calibers are (.22, .204, 6.8SPC, etc.).
I tried searching ar15.com & the internet for inormation with no luck.  
Was he smoking crack or am I

LOL ... he's smoking crack dude ...

The markings on the lower designating caliber mean jack piss.

read his post thoroughly, he knows he needs a different upper he's asking about his lower marked .223/5.56. anyways, that guy is wrong, you may get an upper in any caliber you wish...

Quoted: read his post thoroughly, he knows he needs a different upper he's asking about his lower marked .223/5.56. anyways, that guy is wrong, you may get an upper in any caliber you wish...

I re-read and edited 20seconds later.

no prob, happens to us all

I have like 3 different calibers I shoot 6.5 Grendel, 9mm and 357 Sig, that guy is a moron.

Tell your buddy to put down the pipe.....    

Puff Puff Give, Bro

Thanks for the feedback.  I'm still an AR newbie and when someone says that's illegal, I wanna make sure my shot group is tight.

I D/L'd the 2005 FEDERAL FIREARMS REGULATIONS REFERENCE GUIDE from www.atf.gov and could not find any info related to a caliber conversion/swap/change.   The only info I found on modifying your firearm was concerning machine gun parts, barrel length, foreign rifles/parts, etc.

I found it hard to believe that with ALL the caliber conversions out there for handguns and rifles, if it was illegal or shady, there would be some kind of info about it.  Thanks again for the sanity check.

SW

Quoted: Thanks for the feedback.  I'm still an AR newbie and when someone says that's illegal, I wanna make sure my shot group is tight. I D/L'd the 2005 FEDERAL FIREARMS REGULATIONS REFERENCE GUIDE from www.atf.gov and could not find any info related to a caliber conversion/swap/change.   The only info I found on modifying your firearm was concerning machine gun parts, barrel length, foreign rifles/parts, etc. I found it hard to believe that with ALL the caliber conversions out there for handguns and rifles, if it was illegal or shady, there would be some kind of info about it.  Thanks again for the sanity check. SW

The only time I can even think that it might be an issue, is if you one day decide to "make" a short-barreled rifle out of an existing AR (with a barrel length of less than 16"  which makes it an NFA weapon), in which case your application to the BATF (Form 1) requires you to specify the caliber.  However, many people believe that the original statement still doesn't limit the use to that particular caliber, and in any event you can just send a letter to the ATF afterwards telling them that you are going to use additional calibers.


But for a regular AR-15, there is no restriction, and it doesn't matter WHAT it says on the reciever.  Some people get a kick out of buying receivers that were made during the 1994-2004 years that say "Restricted: Law Enforcement use only" - which is also completely meaningless, and can be used.  The only "restrictions" are on the internal parts - as long as you rifle is a semi-automatic AR, engravings on the reciever are completely arbitrary.  

Go crazy - switch out uppers to your hearts content.  

Go for it, that dude is RETART-TED.

Quoted: ... The only time I can even think that it might be an issue, is if you one day decide to "make" a short-barreled rifle out of an existing AR (with a barrel length of less than 16"  which makes it an NFA weapon), in which case your application to the BATF (Form 1) requires you to specify the caliber.  ....

We had guys here in MD then send in their form with several calibers listed for the lowe (i.e. 22LR, 9mm, 5.56) and have no problems.

Proper caliber should be marked on the barrel,  though if you're one of these anal types you could always buy one of the lowers with the marking: "Caliber: Multi" on it .