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Charmingly unsophisticated
Picture of AllenInWV
posted
This is sort of cross-posted with a thread I started in the Suppressors area.

Since it looks like I'll be getting my .300 upper back soon, I'm taking stock of my AR inventory and calibers and seeing what I want to get next.

I'm sure some of you will find this laughable, but what I have right now is two lowers, a rifle and a pistol, with the rifle waiting to get SBR'd. Once all the paperwork is finished, I'll have an SBR with a .300 and a 5.56 upper. That takes care of <100m.

So what I'm wondering is what does .300 supersonic behave like in short barrels? What about in a 16' barrel? I'm debating starting another build for something in 7.62. As I recall, .300 is supposed to mimic 7.62x39, which is a decent out to what, 200m or so? Is that the supersonic ammo?

What might be better....a 16" .300 for specifically supersonic ammo? Or maybe a 7.62x51 AR?

I really need to find another hobby. Big Grin


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"He is no fool who gives what he cannot keep to gain that which he cannot lose."
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Posts: 14472 | Location: Cross Lanes, WV | Registered: February 05, 2004Reply With QuoteReport This Post
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quote:
Originally posted by AllenInWV:
So what I'm wondering is what does .300 supersonic behave like in short barrels? What about in a 16' barrel? I'm debating starting another build for something in 7.62. As I recall, .300 is supposed to mimic 7.62x39, which is a decent out to what, 200m or so? Is that the supersonic ammo?

What might be better....a 16" .300 for specifically supersonic ammo? Or maybe a 7.62x51 AR?

Contrary to popular belief, 300 blk doesn't mimic 7.62x39, but it comes fairly close. By that same token, 223 doesn't mimic 300 blk, but it comes fairly close.

223 muzzle energies for 16" barrels tend to be in the 1100-1200 foot pound range. 24 inch barrels can increase muzzle energy to 1300-1400 foot pounds.

Supersonic 300 blk muzzle energies for 16" barrels tend to be in the 1300-1400 foot pound range, increasing to 1500-1600 for 24" barrels.

7.62x39 muzzle energies for 16" barrels run 1500-1650 foot pounds, but I haven't seen data on longer barrels.

"decent out to 200m" depends on your definition of "decent". Subsonic 300blk ammo has little more energy than a good handgun, and the bullet's trajectory is a rainbow beyond 100 yards. Supersonic 300blk has higher speed, flies flatter, maintains more energy than subsonic 300blk.

To compare kinetic energy or flight ballistics at given distances, bullet type, expected muzzle velocity, and to a certain extend atmospheric conditions must be known.

7.62x51 is essentially .308 Win, which requires an AR-10 platform, not an AR-15 platform. 308 Win is a huge jump in energy from the other calibers mentioned above.
 
Posts: 4605 | Location: Colorado | Registered: January 26, 2008Reply With QuoteReport This Post
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If you're only buying a 16" upper I would get a 6.8
 
Posts: 131 | Location: DFW | Registered: January 04, 2017Reply With QuoteReport This Post
Charmingly unsophisticated
Picture of AllenInWV
posted Hide Post
I was thinking about another lower. At the moment, I have two....a 'rifle' in the process of becoming an SBR and a pistol. I was kicking the idea of getting a polymer lower to become my dedicated 'pistol' lower, and SBRing the current 'pistol' one. Then picking up another metal lower for whatever 16+" I decide to do next (if I go with an AR).


_______________________________

"He is no fool who gives what he cannot keep to gain that which he cannot lose."
- Jim Elliot
 
Posts: 14472 | Location: Cross Lanes, WV | Registered: February 05, 2004Reply With QuoteReport This Post
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