AR-15 lower compatibility

[mrnkc130]

Very soon I am planning on buying on of those $13,000 ar-15 lowers and to get my moneys worth (one of the reasons i chose m16/ar15 platform) im wondering what all calibers you can use with a standard 5.56 lower by just chaging the upper?

I know 6.8spc (anyone have one? how do you like it?)

22lr (with or without dedicated upper)

5.7x28 with FN type magazine on top is all I have seen for this...

I found all these on DPMS but not sure which of them will work without a dedicated lower for that caliber.

.204 Ruger
.223 Remington
5.56x45mm
6.8mm Remington SPC
7.62x39mm
.243 Winchester
.260 Remington
.338 Federal
6.5 Creedmoor
.458 socom

Also most important question: is it legal to put what ever caliber upper I want on a m16 FA lower? Or do you have to stay with 5.56? Which calibers are compatible with FA m16 lower as opposed to SA?
I sure hope it is, almost get the feeling that it would be too good to be true.

 

[nicholst55]

Let's break your list down into two lists:

List #1

.204 Ruger
.20 Tactical
.20 Practical
5.45X39mm
.222 Remington
.222 Remington Magnum
.223 Remington
5.56x45mm
6mm PPC
6.5 Grendel (and various wildcats)
6.8mm Remington SPC
7.62X25mm Tokarev
7.62x39mm
.458 socom
.50 Beowulf

List #2

.243 Winchester
.260 Remington
7mm-08 Rem
.308 Win
.338 Federal
6.5 Creedmoor

List #1 are cartridges that will work with a standard AR-15 or M16 lower. There are several other cartridges, as well, including several WSSM chamberings and wildcats based on the .223 case. List #2 requires a longer, .308-size upper and lower receiver. As you can see, I added in a few additional cartridges for you that are currently popular in this platform.

One consideration is that inexpensive 'plinking' ammo is not readily available in many of these other cartridges. Several of them are also 'barrel-burners,' and will erode the throat of a barrel very quickly - especially in full auto shooting. The hotter a barrel gets, the faster it erodes. A full auto rifle in one of these cartridges would be a very expensive proposition.

I'm sure that several people will be along shortly to add their favorite cartridge that I didn't mention. There are several, and I didn't try to list them all.

I'm no expert on NFA technicalities, but I believe that you have to list all of the different chamberings of your NFA weapons on the appropriate ATF form, and update it when they change.

 

[mrnkc130]

awesome thanks! i'll have to find out which ones are the barrel burners!

That would be great if you can just add multiple calibers! that was what I was hoping for, i expected with the archaic FA laws and general disdain for FA from our government having one machine gun that can be changed so much into so many different calibers there either wouldnt be a provision for changing or they wouldnt let you.

How about bolt carriers for these other calibers? are they available in FA configurations? or would you have get it machined? 7.62, .22 and 6.8 i think would be the main ones I would want but who knows might want all of them

 

[rogertc1]

FYI. The Beowulf .500 upper comes with a M-16 carrier.

 

[Tirod]

I just bought a stripped lower and it will be marked "multi-caliber." That seems to satisfy it.

The bolt carrier is less of a problem. Some prefer the M16 is they think they need the firing pin shrouded and prefer the increase in mass. Others who don't shoot as much, or who aren't into the operation because things work for them, stick with the AR carrier. And, if it's not broke, don't fix it.

The bolt itself may be caliber specific, like the 6.8. That's where you decide to either tear down the one you have changing uppers, or buy more carriers and dedicate them to that one.

Magazines are the same, caliber specific. Still and all, accumulating a variety of uppers to change calibers is still cost effective, and with a good trigger in the lower, leaves you vary familiar with how it shoots. With the AR, you can buy one $250 trigger - stock , too - and get to shoot your money's worth.

Otherwise, you could have 4-5 others waiting in the rack. At even $120 a trigger, it's an expense.

If someone came up with a swap barrel take down upper, it could be simpler, but the process doesn't lend itself to extreme precision.

 

[briansmithwins]

Some prefer the M16 is they think they need the firing pin shrouded and prefer the increase in mass. Others who don't shoot as much, or who aren't into the operation because things work for them, stick with the AR carrier

If it's for full auto you need the M16 type carrier as the extended under 'tail' of the bolt carrier is what trips the auto sear. An AR type carrier has this 'tail' machined away and won't trip an auto sear.

As far as markings go, the ATF has rejected some recently that were labeled 'multi', at leat according to the arfcom FA forum. Most people (arfcom and uzitalk) are operating under the assumption that you need to list the permanent configuration but can temporarily switch to other calibers.

For example: Say Joe has a 9mm full auto Uzi and that's how it's listed on his Form 4. He gets a .45 ACP conversion. He doesn't need to inform the ATF that he's shooting .45 out of his Uzi. If joe were to sell his 9mm part and in effect convert his Uzi to only .45, he should write a letter to ATF amending his Form 4.

Of course, you safest bet is not to listen to what a bunch of guys on the onter web tell you and to write some letters to the ATF yourself. BSW

 

[Sav .250]

$13,000. Now that`a chunk of change.