Best AR magazine compatible calibers?

[ramairthree]

I am putting this in GD because because you may be an accuracy shooter, a hunter, a tactical seal clubbing, face shooting warrior, a nerdy mechanical engineer with a shooting fetish, a competitor, etc.
and a specific sub technical forum may miss some of this.

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.

Anyways,
I look forward to some interesting stuff. My dream would be a six to seven mm 85 to 100 or so grain bullet pushing 3000 FPS.

[soulezoo]

Your post seems to ask a couple of questions. Is it magazine reliability? Or is it cartridge effectiveness? Or both?

[soulezoo]

The question is important as you list criteria of 6-7 mm projectile at 3000 fps. That leaves you with almost exclusively with AR-10 pattern rifles.

For instance, 6x47 Swiss pushes 105gr. Bergers to about 3150 fps. It uses a .308 boltface. Going up in size and weight will slow the projectile given the same brass. 6.5 Creedmore with 107gr. bullet is about 2950 fps. Creedmores will push the lighter 85 grain bullets well over 3000, but you lose the ballistic advantage of the heavier projectiles.

[grizzman]

By what do you mean effectiveness?

Does terminal performance on the impacted object matter, or will the bullet only impact paper or steel?

Does cartridge availability matter, or will it be strictly handloaded, opening the option to wildcats?

[ramairthree]

Your post seems to ask a couple of questions. Is it magazine reliability? Or is it cartridge effectiveness? Or both?

Yes.
Yes.
Yes.

[ramairthree]

Yes.
For killing shit.
For accuracy.
For trajectory.

Granted, pound for pound humans seem to be easier to kill than most other animals.

What round has the same reliability in an AR platform and magazines as 5.56.
What round has potentially more accuracy?
What round offers improved terminal ballistics.
What ro7nd gives up the least in terms of trajectory and velocity to achieve this.

I find the 300 AAC/BO\Whisper to be a round that gives up too much in velocity and trajectory, with crappier longer range accuracy, and the added insult of not being truly reliable in many AR magazines. I also don’t believe it offers a significant increase in penetration and lethality.

I think/feel a bullet heavier than 5.56 typical loads, but lighter than .308 typical weights, with an intermediate diameter, approaching or meeting 3000 FPS might offer an increase in lethality, comparable accuracy, reasonable trajectory, and reliability on par with 5.56 in the same platform with only the appropriate barrel.

I lack the ability to come up with the RA3 6.66. A 6.66 mm, 6.66 gram, 2666.666 FPS round to prove this.
Nor am I familiar enough and experienced enough with rounds in this range / area of performance to know.

So, basically,
If you are familiar and experienced with a round with more diameter than 5.56 but less than 7.62,
Using the 5.56 case,
Reliable in the AR platform and magazines,
Offering better velocity and trajectory, than, say, 7.62 x 39,
With some concept of its accuracy and ability to kill stuff,
I would like to know about it.

Off hand, I can think of a half dozen or more rounds meeting some of these criteria, but I am not experienced with them.

I always wanted to look into them more, but never got around to it,
But the recent M4 replacement thread made me wonder what would be a viable, potential replacement for 5.56 that did not require new bolts, magazines, platforms, etc.
Hell, maybe the case diameter of 5.56 could be increased by 1mm and still work fine,
And get a 15% increase in case volume.
The bullet would scale up close to .243.
Maybe 90 grain or so.
With a case volume deficit about 20 grains compared to 243 Winchester.
Maybe hit 2800 FPS or so.

Anyways,
I never walked into a meeting where the Army was deciding a new M4 cartridge RFN.
I not infrequently walked into or got called into crisis action planning at the pro level and, despite other relative weakness and shortcomings, with a processing speed and savant like pattern recognition often came up with a plan that was used.

Ten minutes of so on a 5.56 replacement with goal of only changing barrels leads me to the above.

I am simply interested in the results and experiences of others.
I might be totally jacked up, or in the area.

Others have more applicable expertise.

[ABNAK]

What round has the same reliability in an AR platform and magazines as 5.56.
What round has potentially more accuracy?
What round offers improved terminal ballistics.
What round gives up the least in terms of trajectory and velocity to achieve this.


Funny you mention this, as since the weather is shitty here I spent most of the day looking into something I swore I wouldn't do---another caliber AR platform. Specifically 6.5 Grendel. Yeah, different bolt/barrel/mag, but still doable in a non-.308 AR lower. Now, the Grendel isn't going to give you the 3000fps juice you were looking for, but the bullet weights are certainly within the parameters you mentioned. I think you'd be looking at like ~2500fps from a 16" barrel with a 120gr bullet. Supposed to still be supersonic well past 1,000 yds. Obviously the ballistic coefficient must be pretty awesome to pull that off.

From perusing the internet today a Sabre Defence chrome lined upper (purchased before they went under) will be about $450. Then you've got to have a bolt, and the JP Enterprises Enhanced one seems well made at $132 (I can cough up a carrier, but I did see Toolcraft 6.5 nitrided BCG's for $99). Alexander Arms E-Lander 24rd mags are gonna run around $25 each. "Shootin' ammo" is going to set you back about $300+ for 500rds. Yeah, I need to step away from the computer.....

As far as 300BLK is concerned, in a PDW-sized platform the supers edge out 5.56 in the same barrel length (say maybe a 9" barrel). No, you ain't gonna be popping Muj at 600m on some distant Afghan hillside but for CQB out to maybe 200 you'll be good to go. And that PDW is really small and compact. I have no use for a 16" 300BLK because 5.56 blows it out of the water in carbine-length tubes. So for me 300BLK is a VERY niche round but with supers in my wannabe PDW I'll take it.

[Todd.K]

Not going to happen in 5.56 mags. An increase of caliber will mess up the stack, as the cartridge neck runs on one of the ribs of the mag.

300 BLK suffers from not having a magazine with that rib designed for it. Being a shorter case means that you can put the bullet ogive on that rib at the same diameter as a 5.56 neck. But it limits bullet design and many rounds are not loaded like that. Rounds that are loaded like that have been reliable for me.

[gunnerblue]

Funny you mention this, as since the weather is shitty here I spent most of the day looking into something I swore I wouldn't do---another caliber AR platform. Specifically 6.5 Grendel. Yeah, different bolt/barrel/mag, but still doable in a non-.308 AR lower. Now, the Grendel isn't going to give you the 3000fps juice you were looking for, but the bullet weights are certainly within the parameters you mentioned. I think you'd be looking at like ~2500fps from a 16" barrel with a 120gr bullet. Supposed to still be supersonic well past 1,000 yds. Obviously the ballistic coefficient must be pretty awesome to pull that off.

From perusing the internet today a Sabre Defence chrome lined upper (purchased before they went under) will be about $450. Then you've got to have a bolt, and the JP Enterprises Enhanced one seems well made at $132 (I can cough up a carrier, but I did see Toolcraft 6.5 nitrided BCG's for $99). Alexander Arms E-Lander 24rd mags are gonna run around $25 each. "Shootin' ammo" is going to set you back about $300+ for 500rds. Yeah, I need to step away from the computer.....

As far as 300BLK is concerned, in a PDW-sized platform the supers edge out 5.56 in the same barrel length (say maybe a 9" barrel). No, you ain't gonna be popping Muj at 600m on some distant Afghan hillside but for CQB out to maybe 200 you'll be good to go. And that PDW is really small and compact. I have no use for a 16" 300BLK because 5.56 blows it out of the water in carbine-length tubes. So for me 300BLK is a VERY niche round but with supers in my wannabe PDW I'll take it.

I was going to suggest 6.5 Grendel but I thought the OP was interested in staying with the 5.56 case. If that’s the case, 6x45 maybe?

6.5 Grendel and 6mmAR were both designed as performance upgrades to the 5.56 in an AR15. I’ve had no problems with Grendel mags from C-products and Elander and Alexander Arms has done a good deal of fully automatic testing to demonstrate reliability. With IMR 8208 XBR, 123 gr Nosler CC’s and an 18” barrel, I’ve taken my Grendel out to 860 yards with repeatable hits. I’ve no doubt it can go further, just haven’t bothered yet.

I’ve just purchased a Toolcraft Grendel BCG for a budget SBR build. Seems well made, properly staked, etc.

[grizzman]

A search for 223 Remington based wildcats should give the available cartridges, and it's a short list. The 6x45 is likely among the best options.....apparently not.

My guess is that most members of M4C aren't that interested in running wildcats since the 6.5 Grendel and 6.8 SPC are proven performers.

[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

[ace4059]

The 277 wolverine and 300 Blackout are what I would consider short to mid range cartridges. 300 yards max for hunting.

If you are looking for something longer range might look into the 224 Valkyrie. No first hand experience so I don’t know how it would work for hunting at distance.

[1168]

I have very little personal experience with alternative chamberings, but I periodically review what is out there and plan some hypothetical purpose-driven builds around them. The only two that ever make any sense to me are .300BLK and 6.8 SPC.

Blackout for subs, or for ridiculously short barrels, and 6.8 for hunting in states that don’t allow 5.56, or perhaps as a rifle for regions that simply have larger deer.

I always come out of this daydream and stick with 5.56 because I love its trajectory, low recoil, known reliability, and ammo/barrel/bolt/magazine availability.

[ramairthree]

It is a weird day dream.

My first rifle was a 225 Winchester.
Not the fastest .224 gun ever, but pretty impressive to a 12 year old almost 30 years ago.

Imagine my shock, 2 years later, when I bought, very unusual and uncommon at the time, an SP1.
All the lore of the spinning, tumbling, man killing M16 and my first thought on eyeballing the ammo was,
Holy shit! This is just a varmit round. And not even a good one.
Sure enough, my 225 launched 55gr bullets four or five hundred FPS faster than my SP1.

My 30 06 launched 150 grains 100 FPS faster than my buddies .308. Then my 270 did it about 100 FPS faster than my 06. In the woods at short ranges I was cool with a 30 30.

But those early impressions made me partial to trajectories/rounds pushing 3000 FPS,
A fan of those even faster,
But more along the lines of tolerant of 30 30 velocities.

[223to45]

Might want to look into the 224 Valkyrie.

90 grain, it is a neck down 6.8spc.

They say it stays supersonic past 1300yrds.

Sent from my SM-G930V using Tapatalk

[ramairthree]

Valkyrie needs 6.8 or Grendel magazines

[ramairthree]

The sharps round with is Also hitting 2650 with 100 grains and keeps 3000 to 87 grains. Seems to have developed no interest though

[1168]

The sharps round with is Also hitting 2650 with 100 grains and keeps 3000 to 87 grains. Seems to have developed no interest though

TFB did not like that round at all; I don’t remember what was up with that.