What is the largest common caliber am AR 15

I think my goal would be to pick up a standard AR 15 lower and then buy a upper, unless I find some factory built that suits my needs.

I am thinking some thing in the 18"-20" range and larger than 22 caliber that is capable of reliably taking Mule Deer sized game when shot by a youth.


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300 blk shares every part of a standard ar15 save the barrel. Its a 762 round in a necked down 556 casing. Ballistics are decent but I think, could definitely be wrong, that you don't gain anything ballistically significant past 16ish inch barrel.

The round is becoming more and more common, but because I don't have one I cant speak to the ammo availability. But you CAN form your own brass, even if you dont want to ;)
I don't reload so I don't know if this is a good price
Remington Reloading Brass 300 AAC Blackout Primed

Or just buy complete
300aac blackout ammo rifle

The round as a hunter:
300 Blackout hunting, what am I missing? - AR15.Com Archive
There is a lot of info out there about this round.


ETA
A problem with some of the less common calibers that work in an AR lower is the magazines and the availability. They're more expensive by a good deal and often are out of stock. One of the big benefits I see with the 300blk is that you can use the same $9 mags that an AR15 uses and have the rounds feed reliably. Not only that but it uses the same bolt as the standard AR15 since it uses 556 brass. So no oddball bolt to hunt down either.
 
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6.5 Grendel!

I can find both 6.5 Grendel and 6.8 at local LGS. I only do 6.5Grendel as it has in my opinion has better long range ballistics and it uses the same bullets as my 6.5CM. So there less things to look for. My 6.5 guns are my favorite for accuracy/cost/overall value.
 
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What about bolts and magazines? That was a good point to bring up.

Isn't the whole point of a 18" or longer tube to get you better ballistics out past 500 yards?


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The bolts are out there, but they're obviously not as common as standard AR15 bolts and mags.
https://www.rainierarms.com/?page=shop/detail&product_id=1194
LMT 6.8 Enhanced Bolt Assembly. DSG Arms - Defense Solutions Group, inc.
6.5 Grendel Bolt Assembly - Bolts and Extractors by Alexander Arms

Looks like I was wrong on the mag cost and I apologize for my erroneous statement that they're more expensive
6.8 SPC | Mags | AR-15 | Gun Parts by Gun Make & Model
High-Capacity 6.5 Grendel Magazine - Magazines by Alexander Arms

I'm going to shut up now lol because I'm wrong on the availability and cost which would be my only arguments against the 2 6.x calibers. I don't reload so don't have the knowledge to speak to the difficulties or ease at which any of these reload.
 
6.8SPC or 6.5Grendel would fit your bill.

"Common" is a pretty ambiguous qualifier; what is "common" to some is not so "common" to others. Both of these two cartridges have industry support, and are not (or not any longer) proprietary, so they have pretty good acceptance by the community at large. i.e. Parts/components can be had, though they will never be as ubiquitous as say the 5.56mm/.223 components...
 
6.8 spc II.... Parts are more readily available, many more factory ammo options if you don't reload(for example last time I checked Midwayusa had 24 different 6.8 options compared to 7 for the Grendel), and there is more industry support than the Grendel if that's a concern...They are the top two AR15 calipers IMHO. If you reload and are shooting more than 600yds regularly then I'd go Grendel.
 
Since you asked what the largest caliber is, I'd say the .50 Beuwolf would be it. But if you're looking for a big-bore AR, IMO you should go .458 SOCOM. Other than a bolt & barrel, all of the other components are standard. The new 40rd Pmags even hold 14rds of .458. Plus, there's a wide variety of bullets weights & designs available in that cal. I wouldn't consider the round if you don't handload though, unless you're a rich-ass mo-fo that is 8)
 
I think my goal would be to pick up a standard AR 15 lower and then buy a upper, unless I find some factory built that suits my needs.

I am thinking some thing in the 18"-20" range and larger than 22 caliber that is capable of reliably taking Mule Deer sized game when shot by a youth.


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For this I would chose the 6.5 Grendel or 6.8 SPC. They're about perfect for that size game but could even be used on elk if need be. They also have a decent selection of ammo for hunting available.

The big bore rounds are going to push around a youth hunter too much and the 300 BLK can be hit or miss on big game.
 
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capable of reliably taking Mule Deer sized game when shot by a youth.

Isn't the whole point of a 18" or longer tube to get you better ballistics out past 500 yards?

Is your youth hunter going to be shooting at deer out past 500yds?

I suggest the 6.5 or 6.8 like others have said. For the youth hunter I'd imagine 200yds is a long shot.
 
I was "looking for something different" and found the 30 Remington AR. A little slower than 308, but not that much. Shoots up to 160 grn. bullets. Faster than the 6.8 and 308 bullets? What's not to like? I never knew it was out there, till I was thumbing through my reloading book.
 
I was "looking for something different" and found the 30 Remington AR. A little slower than 308, but not that much. Shoots up to 160 grn. bullets. Faster than the 6.8 and 308 bullets? What's not to like? I never knew it was out there, till I was thumbing through my reloading book.

What's not to like? Very little if any parts, ammunition, and Reloading components available..... I do agree that if it had any industry support, readily available factory ammunition, and readily available build components that it's a great round but Remington dropped the ball on it.