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556 saint

Nope.

That 5.56 multi-caliber would refer to calibers approximately the same size as the 5.56.

.308 would require a dedicated lower.

I think the easiest way to check would be to see if the magazine for the caliber you are thinking about will fit in the lower you are using. A .308 magazine will not work in a 5.56 lower. There are also other issues.
 
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Here is a list of the most common rounds used in a 5.56 lower. It also tells you what you have to change to make it work. When it says barrel it would refer to the upper.

I am not an expert on these, but I am sure as the day progresses more people will see this thread and can provide more information.
 
So i can use other caliber uppers on this rifle ?
Yes, you can. You can add 6.5 Creedmoor, 223 Wylde, 224 Valkyrie, 350 Legend, 9mm (with 9mm magwell conversion attachment (most commonly Glock, for glock 9mm mags), plus the ones Grifter mentioned in his reply (and probably more, than in both our lists). Most of these caliber require dedicated magazines (300 Blackout can use 223/556 mags, but all will fit into the AR15 magazine well). Some may also require different Bolt Control Groups (BCG), but many are included when you buy the upper. One important legal reminder, if your AR15 lower has a stock (vs pistol grip), you must keep the barrel length of the upper at 16" or greater. Overall length of the rifle, must be greater than 26" or the ATF could/would classify it as a Short Barrel Rifle (SBR), which requires ATF paperwork you must fill out, plus a $200 Tax Stamp you must pay. (else it's illegal to own).
 
Not an 6.5 Creedmoor.

It requires a .308 (AR-10) lower.
Thanks Talyn, I was just thinking that. It's the only one on the list that Grifter and I mentioned that I don't own, but I've seen uppers chambered in 6.5 CM., so instinctively I just added it to my list.
 
can i buy a 308 upper for my 556 saint multi caliber rifle?
NO! The .308 is an AR-10 the 5.56 is an AR-15 multi-caliber is for example 6.5 Grendel, .224 Valkyrie, .300 BO .350 Ledgen,7.62 X39, 6.8 spec,458 SOCOM .50 Beowulf 450 bushmaster, 223 Wylde these caliber uppers can be used on the AR-15 Lower For the AR-10 a 6.5 Creedmoor, 243,.308 is used on AR-10 Lowers.
 
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Thanks Talyn, I was just thinking that. It's the only one on the list that Grifter and I mentioned that I don't own, but I've seen uppers chambered in 6.5 CM., so instinctively I just added it to my list.
Add the 450 Bushmaster upper (I also own), that fits an AR15 lower.
 
The Noreen BN36 30/06 Upper Receiver (3 versions) won't work on a .308/7.62x51 AR-10 lower for the obvious reasons.
 
My bad I said upper I ment to say Rifle because a 308 lower is too short to accept 3006.I guess you can't call it an AR-10 either. It's referenced as AR -3006 Rifle I wonder if they are as accurate as my Browning BAR in 3006.
 
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