Virginia Gun Owners Forum - VGOF

Once again I turn to this group to answer a noob question that would get me slammed elsewhere. I am nowhere near as educated as I should be on my AR carbine. So, I have to ask - just how universal is the AR lower? Is it truly so simple that I can buy one lower, and as many uppers in as many different calibers as I can find and just swap them out (along with the mags - I know)?

If so - this is very exciting!

The answer to your question is both yes and no. There are basically two sizes of ARs out there at this point, the .223 Remington/5.56MM NATO and the Larger .308 Winchester sizes. I am guessing you are dealing with one of the .223 models. There are multiple rounds/ conversions that are available for your lower. Understand that the most basic issue is "will the round fit in the magazine well?". You hit the nail on the head about the different magazines for each round. Another part that will need to be changed is the bolt, the easiest thing to do is just have a bolt carrier for each upper you have and leave it in the upper. I am going to emphasize safety now, ARs are headspaced with a bolt and barrel as a set, do not believe the rumor that all bolts are the same. Ensure that your bolts and barrels do not get mixed up. If you have any doubt, get the headspace checked on your upper.

Probably the most popular conversions are 6.8 SPC and 6.5 Grendel. Others that I know are available are the .204 Ruger, 7.62X 39MM (Russian AK), and on the big end you have the .450 Bushmaster, .458 Socom and .50 Beowolf. There are also pistol caliber conversions that use submachinegun magazine (they use some form of a magazine well filler block) and .22 rimfire conversion kits that come with a new bolt carrier and a magazine.

The 6.5 Grendel and .50 Beowolf were actually designed by a british engineer and his company is from right here in Virginia, located at the Radford Arsenal: http://www.alexanderarms.com/

grumpyMSG wrote:Understand that the most basic issue is "will the round fit in the magazine well?".

And if you want to shoot something that doesn't, there's always the MGI modular lower with interchangable magwells.

If you want more capacity, you also have the option of beltfed uppers.

mmmmm. Belt-fed upper. Yummy

If you go the .223/5.56 route for your build I highly recommend 5.56. Some newer folks to the AR dont realize that the 2 cartridges are NOT interchangeable. With a 5.56 you can shoot either. With a .223 you can shoot 5.56 but its not advisable since the results are unpredictable. The thickness of the brass and the pressures of .223 and 5.56 are different...

Right, mine is 5.56 and all I have sent thru it is 223, so that's clear to me. What got me started on this questions was, of course, that crate of useless ammo I have. There are a few 545 uppers for the AR platform running around out there but tend to be the same price as some of teh less expensive AK74s.

However, this is all good info for when/if I get get around to building my next AR.

When you buy a cheap AK, it will shoot like a cheap AK. I don't know what the accuracy potential of 5.45X39MM ammo is. I would however offer the SWAG (Scientific Wild Ass Guess) that an AR would shoot it more accurately than an AK. Two parts of the problem with accuracy from AKs come from the type of sights (V-notch and post) and the short sight radius (distance between front and rear sights).

Now, if I could just convince someone who believes the 7.62 AK round is a magical bullet to build an AR in 7.62X39MM with a piston system and see if that is a better rifle than both of them. Personally, I don't think that round is any better.

grumpyMSG wrote:When you buy a cheap AK, it will shoot like a cheap AK. I don't know what the accuracy potential of 5.45X39MM ammo is. I would however offer the SWAG (Scientific Wild Ass Guess) that an AR would shoot it more accurately than an AK. Two parts of the problem with accuracy from AKs come from the type of sights (V-notch and post) and the short sight radius (distance between front and rear sights).

People who shoot it seem to think highly of it. Being much faster and more ballistically efficient than the 7.62x39 it's got a flat trajectory and decent range.

Don't really care for it myself, but dif'rent strokes and all.

Now, if I could just convince someone who believes the 7.62 AK round is a magical bullet to build an AR in 7.62X39MM with a piston system and see if that is a better rifle than both of them. Personally, I don't think that round is any better.

7.62x39 ARs tend not to work that well, something about the bolts breaking. I guess the rim size is too large for the standard AR system?