Looking for some input for an AR build

wdcollard

wdcollard

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Was thinking of making a target shooter/hunting AR. Seriously considering making a 300AAC or 7.62x40. Anyone done this or have any thoughts? I am leaning toward the AAC round due to its availability and the ballistics look similar. It is a sub-sonic round where the 7.62x40 is a sonic round.




300 AAC @zero 100 yards
Ballistics Calculation

Input Variables
Firearm type Rifle Sight Height 1.5
Bullet Weight (grains) 125 Ballistic Coefficient 0.398
Muzzle Velocity (fps) 2275 Temperature 59
Barometric Pressure (hg) 29.53 Relative Humidity 78%
Zero Range (yards) 100 Wind Speed (mph) 0

Ballistics Table in Yards
300 125 gr., 0.398 B.C. www.hornady.com

Range (yards) Muzzle 50 100 200 300 400 500
Velocity (fps) 2275 2173 2074 1883 1704 1539 1391
Energy (ft.-lb.) 1436 1311 1193 984 806 658 537
Trajectory (100 yd. zero) -1.5 0.2 0.0 -6.6 -23.1 -51.5 -94.7
Come Up in MOA -1.5 -0.3 0.0 3.2 7.3 12.3 18.1



300 AAC @zero 175 yards
Ballistics Calculation

Input Variables
Firearm type Rifle Sight Height 1.5
Bullet Weight (grains) 125 Ballistic Coefficient 0.398
Muzzle Velocity (fps) 2275 Temperature 59
Barometric Pressure (hg) 29.53 Relative Humidity 78%
Zero Range (yards) 175 Wind Speed (mph) 0

Ballistics Table in Yards
300AAC 125 gr., 0.398 B.C. www.hornady.com

Range (yards) Muzzle 50 100 200 300 400 500
Velocity (fps) 2275 2173 2074 1883 1704 1539 1391
Energy (ft.-lb.) 1436 1311 1193 984 806 658 537
Trajectory (175 yd. zero) -1.5 1.3 2.3 -1.9 -16.0 -42.1 -83.0
Come Up in MOA -1.5 -2.6 -2.2 0.9 5.1 10.1 15.9


 

7.62x40 WT @zero 100 yards
Ballistics Calculation

Input Variables
Firearm type Rifle Sight Height 1.5
Bullet Weight (grains) 125 Ballistic Coefficient 0.398
Muzzle Velocity (fps) 2400 Temperature 59
Barometric Pressure (hg) 29.53 Relative Humidity 78%
Zero Range (yards) 100 Wind Speed (mph) 0

Ballistics Table in Yards
7.62x40 125 gr., 0.398 B.C. www.hornady.com

Range (yards) Muzzle 50 100 200 300 400 500
Velocity (fps) 2400 2295 2192 1995 1809 1636 1477
Energy (ft.-lb.) 1599 1462 1334 1105 908 743 606
Trajectory (100 yd. zero) -1.5 0.1 0.0 -5.8 -20.3 -45.4 -83.7
Come Up in MOA -1.5 -0.1 0.0 2.7 6.5 10.8 16.0



 
7.62x40 WT @zero 175 yards
Ballistics Calculation

Input Variables
Firearm type Rifle Sight Height 1.5
Bullet Weight (grains) 125 Ballistic Coefficient 0.398
Muzzle Velocity (fps) 2400 Temperature 59
Barometric Pressure (hg) 29.53 Relative Humidity 78%
Zero Range (yards) 175 Wind Speed (mph) 0

Ballistics Table in Yards
7.62x40 125 gr., 0.398 B.C. www.hornady.com

Range (yards) Muzzle 50 100 200 300 400 500
Velocity (fps) 2400 2295 2192 1995 1809 1636 1477
Energy (ft.-lb.) 1599 1462 1334 1105 908 743 606
Trajectory (175 yd. zero) -1.5 1.1 2.0 -1.7 -14.2 -37.3 -73.5
Come Up in MOA -1.5 -2.1 -1.9 0.8 4.5 8.9 14.0
 
Sorry I can't be of help with your actual question, but out of curiosity, what is the main advantage of using subsonic ammo? I have never used it, and always wondered what the reasoning was behind it. Do you already have an AR in .223/5.56, or is this a first time build?
 
I do currnetly have a Pre-ban Bushmaster AR 5.56. From what I understand the sonic round has more power behind it. Sub is good for being quieter and suppressor friendly.
 
Let me clear that I'm not a ballistic expert nor do I play on on TV (regardless how many gun shows are on cable today LOL).

I'm fascinated by fellas who engage themselves in building an AR in these odd calibers. Whatever floats your boat, of course, but the problems you can encounter are mind-blowing.

Since the AR is a direct gas impingment rifle, you've got to be sure that your round will produce enough gas to move the action. Second, you've got to find someone who will drill out a chamber in that caliber for you. Then you're looking at trying to find a magazine that will handle your round. Even today, after years of work, the more common 7.62 x 39 ammo mags have problems running correctly.

Finally, "subsonic" term is used in different ways. A subsonic round could be developed to keep a silenced firearms very quiet, indeed, but you suffer from penetration issues unless the rounds are specially designed. And, then we're talking about rounds that run about 1100 fps, not the 2200+ muzzle velocity you're indicating in your spec above. How would that be sub-sonic? True sub-sonic round will run below 1000fps or less than 761 mph at sea-level.

Can you be more specific in your build requirements? What application would this rifle be used for other than close-in hunting or varmint control?

We're just curious!

Rome
 
No real build "requirements". Would like a larger caliber than the 5.56 and thought this may be a fun build since other than the barrel they utilize all the same components of a standard mil spec AR.
Since the 7.62×40mm WT is based upon the 5.56mm NATO, the only required modification to AR-15/M4 rifles currently chambered for 5.56mm NATO or .223 Remington is a new barrel. Wilson Combat offers barrels and complete upper receiver sets, with barrel lengths offered in 11.3", 16", 18", and 20".

The same for the AAC 300. The ammo is more readily available though where the 7.62x 40mm is still propriatary it looks like.
 
300AAC is not necessarily a subsonic round. You can load it either way. 7.62x40 can also be loaded sub or supersonic.

It doesn't really matter anyway because you're not getting a suppressor here.

Of the two I'd go with 300AAC since it's a SAAMI cartridge with a lot more companies behind it.

wdcollard said:
Was thinking of making a target shooter/hunting AR.
Click to expand...

Neither one is really great at either of those things by the way.
 
I too am thinking about building and researching a "large caliber" AR. YHM sells barrels in 7.62x39 . Also, I could be wrong, but based on my research, a new bolt is also required for both calibers. Another thing, there are companies out there that make dependable magazines.
 
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thehoyt said:
I too am thinking about building and researching a "large caliber" AR. YHM sells barrels in both 7.62x39 and 300. Also, I could be wrong, but based on my research, a new bolt is also required for both calibers. Another thing, there are companies out there that make dependable magazines.
Click to expand...

I would stay away from the 7.62x39 in an AR. The nice thing about the 300AAC and similar calibers is that they use a standard .223 case as the parent. Same bolt face, same mags.
 
For something different, how about the Tactical 20 or the 20 VarTarg?

At least those would have some practical hunting use in Massachusetts.
 
Terminator03 said:
Do you really think you can have a suppressor here?
Click to expand...

Does it really matter? I realize the temptation is high to paint someone as a mall ninja, but this comment is much in the same vein as the stuff that happens when people have a thread about pmags and then some guy comes in announcing that they are ILLEGAL IN MA as if MA is somehow the center of the universe. [laugh]

jasons said:
You must be reading the internwebz.
Click to expand...

.300 AAC does suck less than a lot of the other wildcats, for what it is. It's not useful beyond a few hundred yards, much like 7.62 x 39, but at least it feeds correctly in an AR without resorting to using heinous crap for magazines. [laugh]

-Mike
 
I did a bit of research into it and want to build an SBR for my fiance, and am thinking of going with 300AAC. I will likely wait until I am reloading to go this route, even though you can get it for close to .50 cents a round. I would not build a full length rifle in this caliber, but the numbers are very impressive on short barrels when compared to 5.56 coming out of an equal length barrel, especially inside of 100 yards (primary purpose of an SBR/PDW type setup). For a full size AR stick with 5.56, or go with something like an AR-10 platform.

The ONLY difference required of the rifle with .300 AAC is the barrel and chamber. Everything else is the same as the 5.56 setup, same mags, same bolt, same upper. WRT to subsonic ammo, it is nice if you are suppressing the rifle, otherwise I wouldn't waste your time. Think of 300AAC as a useful breach in the gap between a sub gun and a rifle.

Mike
 
I do still plan to get an AR-10. I just thought the .300 AAC would be good to take to the range and do some varmint hunting with. No one so far has told me why it sucks so bad.
 
wdcollard said:
I do still plan to get an AR-10. I just thought the .300 AAC would be good to take to the range and do some varmint hunting with. No one so far has told me why it sucks so bad.
Click to expand...

It doesn't suck, it's just not designed for what you've been taking about. It's basically an under-powered .30 caliber round designed for short range use with a suppressor. You've been asking for a hog hunting round that's good for target shooting and also varmints and there are better calibers for all three of those things.

But do whatever you want. You don't need a good reason to build an AR and if you think it's cool go for it.
 
jasons said:
It doesn't suck, it's just not designed for what you've been taking about. It's basically an under-powered .30 caliber round designed for short range use with a suppressor. You've been asking for a hog hunting round that's good for target shooting and also varmints and there are better calibers for all three of those things.

But do whatever you want. You don't need a good reason to build an AR and if you think it's cool go for it.
Click to expand...

This+;
Even if suppressors are allowed, most likely they aren't allowed to hunt with.
I've got a buddy with a Colt in 7.62x39 and it has worked well. .308 is better in every way.
 
300AAC is really only great on an SBR, a can, or both. It's also still pretty expensive ($.50 per round is about as low as I have seen them)... Why not build an SBR? If you're set on one of those rounds, I'd choose 300AAC every time. That said, a good friend of mine bought a knights armament 300acc and traded it for another .556 upper a couple months later. He thought is was going to be the best thing since sliced bread and in the end it wasn't worth it on a 16 inch gun... To each his own, but IMHO that round is best out of an SBR
 
Again, if you are just looking for something different, I'd say go for a .17, .19, or .20 caliber based off the .223 case. It would allow long range shooting, and the ability to watch your round hit the target in many cases. I don't have one, but I would sure put it on my list of something to get for fun, and also for hunting.
 
300AAC is really only great on an SBR, a can, or both. It's also still pretty expensive ($.50 per round is about as low as I have seen them)... Why not build an SBR? If you're set on one of those rounds, I'd choose 300AAC every time.
Click to expand...

+1

I have also been looking at the 300 blackout for an SBR build. Ballistics seem to be superior with the intended purposes of saying inside 100 yards, and its something different. The ability to use standard AR mags is a huge plus for me (otherwise i'd consider a 6.8 spc or something similar) and later on if i decide to move out of state, a supressor is only another tax stamp away, which is where the 300 blk really shines.
 
wdcollard said:
The 7.62x40 also utilizes all the innards of the AR.
Click to expand...

(Edit: never mind, was thinking of the 7.62x39)

Still 7.62x40 is a proprietary caliber that only a couple companies make parts for. I'd stay away.
 
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