AR-15 in .300BLK (300 Blackout)

[whiskeytangofoxtrot]

As soon as I find a 7.5 Noveske barrel, I'll be starting my build...I hate awesome new fun calibers, they cost me too much.

 

[dubsac]

As soon as I find a 7.5 Noveske barrel, I'll be starting my build...I hate awesome new fun calibers, they cost me too much.

I believe noveske shortest is an 8 inch in 300BLK if im not mistaken, though make a 7.5 in 556.

 

[esrice]

I believe noveske shortest is an 8 inch in 300BLK if im not mistaken,

Yeah just go 8". . . .

 

[dubsac]

esrice with shooter getting an upper in 300blk it looks like its your turn.

 

[esrice]

esrice with shooter getting an upper in 300blk it looks like its your turn.

Not gonna argue with that.

 

[shooter521]

I believe noveske shortest is an 8 inch in 300BLK if im not mistaken, though make a 7.5 in 556.

Indeed.

Noveske 300 Blackout Barrel - 8"

 

[Redneckbuckeye]

Why not just get a 7.62x39 upper if the ballistics are similar?

 

[jblomenberg16]

Why not just get a 7.62x39 upper if the ballistics are similar?

1) 7.62x39 requires a unique bolt; .300 blackout uses the same bolt as the 5.56 / .223.

2) 7.62x39 requires unique magazines; .300 blackout uses standard 5.56 mags

3) 7.62x39 has a limited selection of bullets (.311 diameter) to use for the folks that reload; .300 blackout uses standard .308 bullets.


#1 and #2 alone are the biggest reasons, and #3 is the icing on the cake.

 

[Clay]

7.62x39 ARs aren't known for their reliability either IIRC, which goes back to the funky mags and feeding issues more than anything.

 

[Hop]

Does an 8" 300 BLK Noveske still give you enough velocity to knock some stuff down if shooting supersonic? I want it to beat the energy from a 5.56 round 100-300 yards downrange if needed.

 

[jblomenberg16]

Does an 8" 300 BLK Noveske still give you enough velocity to knock some stuff down if shooting supersonic? I want it to beat the energy from a 5.56 round 100-300 yards downrange if needed.

Very rough numbers based on some bullets I had in my database. These are not exact since I haven't actually done any load development to confrim, so just rough "hypothetical" comparison

Subsonic 220gr with a 1000FPS muzzle velocity.

Energy@
muzzle: 488 lb-ft
100yd: 453
200yd: 423
300yd: 397


Supersonic 110gr with a 1900 FPS muzzle velocity (rough swag of what yo might get from an 8" barrel)

Energy@
muzzle: 882 lb-ft
100yd: 756
200yd: 646
300yd: 550



Compared to standard M193 Ball (55gr) @ 3000 FPS from a 16" barrel (again rough number to make the math easy)

Energy@
muzzle: 1099 lb-ft
100yd: 845
200yd: 641
300yd: 477




So, to answer your question, the 5.56 makes up for its light projectile with velocity. Since the equation for energy is 1/2*m*v^2, the velocity component does more for you than the mass component.

Supersonic .300BLK is certainly no slouch, and would do the trick, but won't have the same "Knock down" energy of a full power 5.56 round.

 

[paramed60]

300 Blackout

Who is carrying the uppers now? I really want one. Looks like they are gaining popularity and prices may be coming down slightly.

 

[Tombs]

I'd be interested in one if they could get the velocity up and get it to shoot a little flatter out to longer ranges in "bulk grade" ammunition.

I don't care how light they have to make the projectile to do it, if they can get some better long range performance out of it. Until then the 6.8 keeps looking more and more attractive. Hell, you can go pretty heavy on it if you need to for suppressed applications as well.

Logistically speaking, I know why they did the blackout the way they did, the numbers just don't do much for me, even though I ohh and ahh at the round on a regular basis.

 

[Hop]

But the 6.8 requires a new bolt & new mags (that may or may not feed correctly and cost a bit more). I think if I had somewhere to shoot that far I'd rather go with a 6.5 Grendel over the 6.8. The BLK is more of a CQB <200-300yrd setup.

Found some more performance data here:
.300 Blackout Accuracy & Velocity Data « Vuurwapen Blog

 

[Redneckbuckeye]

1) 7.62x39 requires a unique bolt; .300 blackout uses the same bolt as the 5.56 / .223.

2) 7.62x39 requires unique magazines; .300 blackout uses standard 5.56 mags

3) 7.62x39 has a limited selection of bullets (.311 diameter) to use for the folks that reload; .300 blackout uses standard .308 bullets.


#1 and #2 alone are the biggest reasons, and #3 is the icing on the cake.

Mags are cheap/ relatively, sounds like most of you are building dedicated uppers anyway as far as the bolt goes....cheaper ammo, cheaper upper, some manufacturers have fixed the mag feeding issues, seems like it makes more sense to me.

 

[jblomenberg16]

Picture of my new baby. Broke it in Yesterday.
.

Upper is a 16" CMMG. Lower is Spikes, VLTOR stock, MOE + etc. Shoots very well, and I'm really digging the CMMG handguard. It is very thin and light weight, and has rail sections that can be moved to multiple locations on the handguard to suit.

 

[pierce195]

Picture of my new baby. Broke it in Yesterday.
.

Upper is a 16" CMMG. Lower is Spikes, VLTOR stock, MOE + etc. Shoots very well, and I'm really digging the CMMG handguard. It is very thin and light weight, and has rail sections that can be moved to multiple locations on the handguard to suit.

Nice looking rifle, what happened to the short barrel?

 

[malern28us]

1) 7.62x39 requires a unique bolt; .300 blackout uses the same bolt as the 5.56 / .223.

2) 7.62x39 requires unique magazines; .300 blackout uses standard 5.56 mags

3) 7.62x39 has a limited selection of bullets (.311 diameter) to use for the folks that reload; .300 blackout uses standard .308 bullets.


#1 and #2 alone are the biggest reasons, and #3 is the icing on the cake.

I guess if I was on a "super secret" mission this would be icing as you say. The cold hard truth is you arent gonna carry both a 5.56 and 300 BLK upper and ammo with you if you ever "have" to use them. Looks like there isn't really any advantage. The ammo price difference speaks volumes.

 

[jblomenberg16]

Nice looking rifle, what happened to the short barrel?

The 16" upper is just to tide me over until the paperwork and stamp come in for the SBR.

 

[pierce195]

The 16" upper is just to tide me over until the paperwork and stamp come in for the SBR.

That makes sense.

P.S. If you bring you new toy along, you can go a "super secret" missions with me.