[jn_fsu]

Yes I'm already looking ahead... Why? Well because I can!
Though it will probably be next spring before I start I need to do my home work in the mean time. I have one more spare lower and would like to build a DMR/SPR type rifle with a 18-20 inch barrel. Originally I was just going to go 5.56 because its cheaper to shoot but I'm yerning for something different.
My original thought was 6.8 SPCII , then the AAC 300 popped up and I've also read into to the 6.5 a bit. Anyone know the difference between the 6.5 Grendel and 6.5 Creedmoor or can explain if there is one? I'm not sure what yardage I want to shoot out to. If I make special trips I can go to a range out to 1000 yards but that won't be often. Thats ok because between ammo cost and range axcess I won't rack up alot of shooting with it like my other AR(s). This is more of a speciality build for me. So please enlighten me on the choices I'm looking at. The more info the better. Feel free to make your replies as long as you want. Theres no such thing as too much information in my book and I love to read and learn. Thats alot of why I'm on here!
PS no I haven't tried search yet... But I will eventually!

 

[John A.]

The 300 blackout, although do have supersonic (regular) loads, really shine being used quietly with the subsonic loads and a suppressor. That was really what it was designed for.

The 300 blackout loads are anemic when compared to the 6.8, which is better in ballistics, penetration, and power.

The 6.5 has a reputation for 308 "like" ballistics out of an AR15.

I personally went with 6.8 because I wanted a medium/big game hunting gun and the 6.8 has a huge following for that.

I wouldn't be shooting at extended ranges, and felt the added power the 6.5 offers would be wasted. Plus, the 6.5 ammo is fairly difficult to find in meaningful numbers at any price.

The 6.8 has a lot of companies loading for it and more than 25 different bullets and choices. And if suppressor use is what you have in mind, Corbon markets a subsonic round for it as well.

Even a new place in Texas offering hotter SPCII combat/tactical loads for $15 a box.

If you choose a 6.8spc, then the big things to look for would be SPCII chamber or even 6.8x43 chamber is more preferred to get the most out of the platform.

Hope this helps buddy.

 

[Mephis]

People can bash the 6.8 all they like in favor of the 6.5, but looking things over on paper, I think the 6.8 fills the role best.

The 300 blackout is very interesting to ME, but wouldn't be ideal for most people. One positive with it is that it can use existing 300 whisper ammunition. I'd say with super sonic ammo you're limited to around 300 yards without making extreme corrections. I can't really express how much interest I have in this round, and how its performance matches exactly what I want from the AR platform. I just wish the 7.62x40mm would have been made popular instead.

6.8 just offers the majority of things most people seek in getting something better than a 5.56 in pretty much all areas of performance. While a 5.56 may shoot flatter, and some claim further, it won't have the energy past 300 yards that's really necessary for doing anything. The 6.8 gives you that extra edge to put the energy out there even though you're dealing with a considerably less-flat shooting round. If you're just punching holes in paper, none of this will be of any interest.

6.5 should be reserved for a small niche crowd looking to target shoot at extreme ranges. While it's better in some areas than the 6.8, those differences are exaggerated. For practical use it's not going to be any better or worse. It also won't come close to matching a 308's power, so don't drink the koolaid on that one. It is an exceptionally accurate round that would be the top choice for someone looking to do long range silhouette shooting. If you're mostly punching paper past 300 yards, and want to push the AR platform to the next level, it's ideal.

20" barrel with a 1:8 twist and 77gr bullets in .223/5.56 shouldn't be over looked though. It sure is nice to have the option of cheaper ammo. Realistic performance differences won't be as huge as you may think. I'm just generally opposed to different rounds in the AR platform because of cost and ammo availability. It turns a great fun shooting gun into a safe queen when you're tight on cash. Plus with that set up, you'll have everything you want and only have to change ammunition to seek different performance. As boring as it may be, it's the most practical.

 

[treehugger49]

I think most of your questions were addressed, but the 6.5 Creedmore is a longer action cartridge that would require the AR-10 platform, I believe.

I'm partial to the 6.8 SPC, having recently completed a build project for a dedicated hunting rifle. It is an ARP 6.8X43 18" SPR SS barrel, 12" MI SS free-floating foregrip on a Mega upper receiver over a Mega Gator lower w/ RRA LPK, NM two-stage trigger and Vltor EMOD stock.

 

[Mephis]

6.5 creedmore is a necked down 308. Just fills the gap between 243win and 7-08.

 

[rsilvers]

300 AAC Blackout is between 5.56mm and 6.8 in power, but does not require special magazines or bolts like 6.8, and the brass is much cheaper. For people who want something larger caliber than 5.56mm in their standard size AR, it is the easiest solution. You can deer hunt in states which do not allow 5.56mm, and you get more power up close, making it ideal for home defense.

SilencerTalk • View topic - 300 AAC BLACKOUT FAQ

 

[Mephis]

300 AAC Blackout is between 5.56mm and 6.8 in power, but does not require special magazines or bolts like 6.8, and the brass is much cheaper. For people who want something larger caliber than 5.56mm in their standard size AR, it is the easiest solution. You can deer hunt in states which do not allow 5.56mm, and you get more power up close, making it ideal for home defense.

SilencerTalk • View topic - 300 AAC BLACKOUT FAQ

300 blackout does require a different magazine.

The ribs inside of magazines where a 5.56's shoulder normal sits against cause issues with the 300 blackout.

Best magazines to use are 6.8 specific magazines. But yes, it doesn't require anything besides a barrel change and magazine.
That said, unless you're running a can, there's not much of a point to it. 6.8 will develop more power in super sonic loadings.

 

[rsilvers]

The ribs can be an issue if you are unaware of how to set the OAL to hit the rib at the 0.250 diameter part of the ogive (the diameter of a 5.56mm case neck).

Factory ammo has already taken care of this, and Remington ammo was specifically designed for normal magazines, and tested for tens of thousands of rounds in USGI magazines and Pmags.

Also, 6.8 magazines have an incorrect feed lip width, and would not be a good way to go.

 

[Mephis]

When the OAL is set for that, a large amount of capacity is lost and further cripples the round's performance.


When this stuff has become common place, and gets out of its infancy it will be worth a look but for the time being it's pretty much an experiment still. I would like to believe it has some advantages in supersonic loadings but considering the way things look right now, it's not nearly as good as it could be. The russians moved to 5.45 for a reason, if 7.62x39mm was superior that wouldn't have happened. I have no doubt that for suppressed applications the 300 blackout is excellent, although someone should have just copied the 9x39mm instead. The .358 grimlin exists but I don't believe it's even got more than 1 web page worth of info on it. Hell of a lot more powerful in supersonic loadings than the 300 blackout is though.

There's always the 30 remington AR...

 

[rsilvers]

We can go over a few bullets and OALs I am talking about...

For 220 subsonic, 2.120 OAL seems best overall. It is subsonic, and there is no issue with a loss of case capacity.

For 110-V-MAX, about 2.068 seems best. That does not even fully fill the neck, so also - case capacity is not an issue.

For Rem 125 AccuTip, 2.130 seems best - also - no loss of case capacity.

Remington 125 Premiere Match ammo uses a custom 300 AAC BLACKOUT specific bullet and the OAL can be up to 2.26. This bullet will be for sale in bulk.

Remington UMC - not out yet - but also a new bullet design - fits magazine perfectly even with ammo loaded to 2.26 OAL.

 

[Mephis]

If someone can manage 2400-2500fps with a 125gr bullet from a 16-18" barrel using 300 blackout, I'd be sold.
Seems as if a good bit has changed since I last researched it.

 

[rsilvers]

It can't go that fast - that is more of a 30 RAR thing (125 at 2800 fps from a 24 inch barrel), but we tuned the 125 AccuTip to penetrate 12-18 inches even from a 9 inch barrel downrange. So we are doing custom bullets to be optimal at the velocities it does reach.

 

[John A.]

A 24" barrel isn't very common is it? Wasn't the blackout designed for short(er) barrels in mind? How does the same bullet work shot out of a 9 inch barrel? Or 16 inch?

Is that 125 gr accutip bullet in the video supersonic or subsonic and (approx) what is the top speed the blackout capable of?

 

[rsilvers]

Supersonic.

 

[John A.]

I apologize. I was asking more questions as you were replying and I was editing my post at the same time.

I just wanted everyone to know that he wasn't skirting my questions.

It was just in the timing.

 

[rsilvers]

A 24" barrel isn't very common is it? Wasn't the blackout designed for short(er) barrels in mind? How does the same bullet work shot out of a 9 inch barrel? Or 16 inch?

Is that 125 gr accutip bullet in the video supersonic or subsonic and (approx) what is the top speed the blackout capable of?

24 inches is the standard barrel length for 30 RAR.

16 inches is the standard barrel length for 300 AAC BLACKOUT.

The 300 AAC BLACKOUT will do 2450 fps from a 16 inch barrel with 110 grain bullets - but factory 110 grain ammo will probably be about 2400 fps.

 

[Mephis]

Oh I didn't know it could hit 2400 with anything. That's up there with a 6.8, but has the option of far heavier bullets, so I suppose it's all around better besides availability.


That might me a option for me when I decide to switch calibers then. I'd like to have a light profile non-threaded 18" in 300blackout at some point.

I think if it could be dialed in to have a 300-500yard operating range, it'd suit me perfect. 9x39mm manages it with a 250gr bullet, I suppose this would do so even better. 240gr 30cal has to have a lot better BC than a 250gr 35cal.

 

[rsilvers]

2450 fps about 58,000 psi. 2400 fps is below the SAAMI spec of 55,000 psi.

9x39 is cool but subsonic only.

I did just have an AK made in 300 AAC BLACKOUT and it will shoot subsonic. It has a 1:8 barrel.

300 AAC BLACKOUT supersonic ammo from a 16 inch barrel will start to drop to 1200 fps around 550 yards. I did shoot it at 600 though, and hit a 3 inch X-ring once and the 10 ring a few times.

 

[rsilvers]

9x39:

Ancester of the 300 AAC BLACKOUT:

 

[John A.]

but factory 110 grain ammo will probably be about 2400 fps.

Yeah, those are pretty good numbers. Or at least better than some I have been hearing. But at the same time, if it maxes out at 2400, then the numbers are only going to go down as the bullets get heavier.

To keep things in perspective, the 110 gr 6.8 Hornady vmax get about 2635 fps average, so only a couple hundred fps advantage there. And likely due to pushing a smaller diameter bullet.

Obviously for this topic in the differences the 85 and 90 gr 6.8 push nearly 3,000 fps, but a much lighter bullet in comparison, but I'm trying to keep things in the same context without sounding like I'm bashing because I'm not. I'm just trying to find something to compare it to that's relatively close in numbers.

110 gr .30 Carbine = ~2000 fps
110 gr .32-20 = ~2100 fps
110 gr 30 Blackout =~2400
123 gr 7.62x39 = ~ 2640
110 gr 30-30 = ~2684 fps

Obviously, I'm not going to cover all the 30 caliber out there because they typically only go up in power in both speed and bullet size (30-06, 308, 7.62x54 and 300 magnum, etc) and the blackout was never meant to be in that league, but the ones I listed above are pretty common deer hunting rifles that hunters are familiar with.

So conservatively, the (supersonic) blackout maxes out at roughly the middle of the road where it comes to light 30 caliber brush guns.