Best AR magazine compatible calibers?

[SomeOtherGuy]

My question is,
In terms of range, trajectory, effectiveness, reliability, etc. what is the best AR15 magazine caliber you have direct experience with?

I only have AR15 platform experience with 5.56 and 300BO.
With 300 BO I have found issues with actual 100% mag reliability.
I am not impressed with the hypersonic to be honest, and with the subs I often find myself asking why the hell I did not just get a 9mm AR.

Ooooh hypersonics, that's awesome. What cartridge? Even .220 Swift doesn't reach hypersonic.

I wonder if you could load a 10 grain rod into a 5 grain sabot in a .300 BLK and get to 5500fps... need to call up some aerogel makers.

Personal experience: same two as you. Both work OK, neither is perfect. I wonder why 6x45mm hasn't taken off, since it basically gives you a 10 grain heavier bullet with the same muzzle velocity as 5.56x45mm loadings, same magazine, no apparent compromises.

[Todd.K]

6x45 will not stack correctly in a 5.56 mag.

6mm was passed over in the SPC design as not offering enough terminal performance increase. The SPC was all about OTM terminal performance for military use, so bonded or copper bullets may change that.

[Clint]

How about the .277 WLV?

Same easy button as 300BLK, but in 6.8mm.

Uses .233 parent brass and gets about 90% velocity compared to 6.8SPC

[ramairthree]

Does not have to happen exactly.

But how close?

We know we can come around 2700 FPS or so with 77 grain .224 bullet.
We know we can do around 2200 FPS with about 125 grain 7.62.

Some guys are doing .264 bullets in the 100 grain range about 2400 FPS.

I want a heavier, bigger bullet than the first and more velocity than the second.

We know we can come around 2500 FPS or so with a 90 grain 7.62.

What is the maximal we can do with the 5.56 parent case?
It’s going to be under 30 grains of powder. A 90 grain .264 bullet at about 2600 FPS?

Does that offer an advantage over any 5.56 loading?

Can you update 100s of thousands of rifles to it with just a new barrel?
If you can’t grt it to work with AR mags as is, can you replace just the follower?

Will another mm of diameter 5.56 case five enough additional powder capacity?will those work in AR mags?
If not will they work with a follower?

Just wondering what the hard limit is for the standard AR rifle and mag.

At least until brass is replaced by a solid shaped like a 5.56 case hard powder with a primer in one end and hole in the other to seat the bullet.

[grizzman]

Are you honestly looking for something to purchase, or is this just hypothetical?

[ramairthree]

Ooooh hypersonics, that's awesome. What cartridge? Even .220 Swift doesn't reach hypersonic.

I wonder if you could load a 10 grain rod into a 5 grain sabot in a .300 BLK and get to 5500fps... need to call up some aerogel makers.

Personal experience: same two as you. Both work OK, neither is perfect. I wonder why 6x45mm hasn't taken off, since it basically gives you a 10 grain heavier bullet with the same muzzle velocity as 5.56x45mm loadings, same magazine, no apparent compromises.

Oops, wrong word.

Are you honestly looking for something to purchase, or is this just hypothetical?

Both.

How about the .277 WLV?

Same easy button as 300BLK, but in 6.8mm.

Uses .233 parent brass and gets about 90% velocity compared to 6.8SPC

Interesting. 2650 GPS with 100 grains.
Closest I have seen.
I did not know about it.

[ace4059]

I was going to recommend 277 wolverine but I see Clint already mentioned it.
2850 FPS with a 90 gr bullet.

[Todd.K]

It's not the follower, it's the internal shape where the ribs are pressed in to the mag that keeps you from being able to go bigger.

Remember the 6.8? Commercial loading with pressure equipment is not going to equal wildcatters reloading to "pressure signs".

[grizzman]

The .277 Wolverine does look promising, as long as it's reliable.

Starline even makes brass for it.

There's no doubt that it'll offer superior terminal performance compared to 5.56, but I'll need to spend some time with Sierra Infinity to see how well it'll fly.

I use 110 grain Pro-Hunters and 115 grain SMKs in my 6.8 SPC, but their BCs are outclassed by a 77 grain SMK and especially a Tipped MatchKing. I consider bullet selection the 6.8's greatest negative aspect.

[Firefly]

You could look into 25-45 Sharps

Not my cup of tea but it looks interesting and sounds like something a cowboy would carry