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Author Topic: .308 info
5.56
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Folks.

Going to a shoot this weekend so I went to the range to chronograph and run a some tests.

175 SMK BTHP 45 grains of varget

16" AR10 2460fps subsonic at 1067 yards
20" AR10 NM 2585fps subsonic at 1143 yards
26" 700 BDL PSS 2699 subsonic at 1211 yards

190 smk did not perform well with H380 max load of 48gr

even a 16" bble is good to 1000 yards with 175 SMK's

5.56

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Breacher
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I have always been under the impression that pushing .308 Win out of any barrel shorter than 18" is just a waste of gunpowder. If you want to make .30 holes and have some decent short to midrange penetration out of a smaller weapon system, then it might as well be 7.62X39 since most of the ammo in production in that caliber was optimized for the 161" AK anyway, but if you do run it through a longer barrel (RPK, RPD, SKS) then you get a little bit more reduced flash signature and slightly higher performance, just you are not losing anything by chopping the barrel down.

I know 5.56 short barrel tactical carbines are all the rage right now, but I don't see any of them giving real world performance that is significantly better than 9mm +P out of barrel lengths typical of the various Euro subguns and semiautos based on those platforms.

I a very curious however, what sort of performance you are getting out of the subsonic .308s out of the longer barrels, like that 26". In theory, if there is background noise roughly on the order of modern freeway traffic then the enemy is unlikely to determine the direction of attack in the first few shots. Can the subsonic cycle the action on a semiauto?

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Life liberty, and the pursuit of those who threaten them.

Trump: not the president America needs, but the president America deserves.

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Lord Vader
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quote:
Originally posted by Breacher:

I a very curious however, what sort of performance you are getting out of the subsonic .308s out of the longer barrels, like that 26". In theory, if there is background noise roughly on the order of modern freeway traffic then the enemy is unlikely to determine the direction of attack in the first few shots. Can the subsonic cycle the action on a semiauto?

”Can the subsonic cycle the action on a semiauto?”


Brother the way I am reading what 5.56 posted is that he meant that those rounds went from Supersonic to Subsonic at his listed Ranges, not that the Rounds were Subsonic out of the barrel.

A velocity of 2460 fps out of the 16in barrel is Mach 2.18 and is not Subsonic.

And the velocities out of the other listed weapons and barrel lengths is even greater.

--------------------
VINCE AUT MORIRE (Conquer or Die)

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5.56
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Folks

The information is for what you can do with the .308. 168gr smk bthp are not very good beyond 850 yards, They drop subsonic and act erratic.

What it means is my 16" carbine will still be able to give decent performance out to 1,000 yards using 175's.

My 20" will be used in competition this weekend from 100 meters to 1,000 meters. Optic will be a 6x trijicon ACOG. I will be using a Barrett M82A1 CQC 20" with a 6X trijicon ACOG. This will be used from 550M to 1,000M and a 6X works just fine at 1,000M

My 20" will perform in excess of 1,000 meters, Do you REALLY know what your rifle is capable of? Until you get up from the puter desk and get to the ranges you are not up on what you and your rifle can do.

I try to operate on the premise....If I can see it, I can hit it! At previous events, I can tell you my max effective range for me is 2,100 meters with a .50 Cal and that is with the bullet gods smiling at me on that day! lol

5.56

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5.56
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This is the profile for a 175 SMK BTHP from a 16" BBL. You tell me if it is a waste of gunpowder. At 400 yards the 175 has more Foot pound energy than a 223 55gr at 3200 FPS has at the muzzle.

At an Elevation Angle of: 0 degrees
Ballistic Coefficients of: 0.505 0.496 0.485 0.485 0.485
Velocity Boundaries (Feet per Second) of: 2800 1800 1800 1800
Wind Direction is: 3.0 o'clock and a Wind Velocity of: 10.0 Miles per hour
Wind Components are (Miles per Hour): DownRange: 0.0 Cross Range: 10.0 Vertical: 0.0
The Firing Point speed of sound is: 1148.01 fps
The bullet drops below the speed of sound on the trajectory (1148.19 fps) at: 1067 yards
Altitude: 1100 Feet Humidity: 78 Percent Pressure: 29.53 in/Hg
Temperature: 85 F
Data Printed in English Units
Velocity(Ft/Sec) Energy(Ft/Lbs) Bullet Path(inches) Bullet Path(1 MoA) Range(Yards) Wind Drift(inches) Wind Drift(1 MoA) Time of Flight(Seconds)
0 2460 2351.1 -1.6 0 0 0 0
100 2301.3 2057.5 2.49 2.4 0.73 0.7 0.1261
200 2148.3 1793.1 0 0 3.01 1.4 0.261
300 2001.4 1556.3 -10.03 -3.2 7.01 2.2 0.4057
400 1860.9 1345.5 -28.75 -6.9 12.91 3.1 0.5612
500 1725.9 1157.3 -57.53 -11 20.91 4 0.7286
600 1597.8 991.8 -98 -15.6 31.25 5 0.9093
700 1479.1 850 -152.1 -20.7 44.15 6 1.1045
800 1371.2 730.4 -222.13 -26.5 59.79 7.1 1.3153
900 1275.6 632.2 -310.67 -33 78.29 8.3 1.5424
1000 1194.1 554 -420.59 -40.2 99.66 9.5 1.7858
1100 1127.3 493.8 -554.9 -48.2 123.78 10.7 2.0448
1200 1074 448.1 -716.6 -57 150.4 12 2.3179
1300 1030.2 412.3 -908.48 -66.7 179.23 13.2 2.6037

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Archangel1
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5.56,

I understand you to say that if reloading or purchasing non-subsonic 7.62 x 51 ammo, the 175gr projectile offers better 1000 yard performance than 168 or 190 projectiles in 16" to 26" barrels. I was under the impression that 168 bthp was standard issue for law enforcement and military overwatch.

Thank you for the knowledge. I will pass it along.

--------------------
"Power tends to corrupt and absolute power corrupts absolutely. Great men are almost always Bad Men." Lord Actin 1887

I fear we live in evil times...

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5.56
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Sir,

You are most welcome!

5.56

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Breacher
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I was confused and then re-read the charts. Thanks for the info. I guess it is personal preference, but my opinion has been that if you take a cartridge type that was engineered for full rifle length barrels and start chopping barrel length, then you might as well chop case capacity. IE, drop 5.56 down to 5.45 or even 5.7, and 7.62 down to 7.62X39

--------------------
Life liberty, and the pursuit of those who threaten them.

Trump: not the president America needs, but the president America deserves.

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Breacher
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I was confused and then re-read the charts. Thanks for the info. I guess it is personal preference, but my opinion has been that if you take a cartridge type that was engineered for full rifle length barrels and start chopping barrel length, then you might as well chop case capacity. IE, drop 5.56 down to 5.45 or even 5.7, and 7.62 down to 7.62X39

--------------------
Life liberty, and the pursuit of those who threaten them.

Trump: not the president America needs, but the president America deserves.

Posts: 6705 | From: Western States | Registered: Sep 2002  | Report this post to a Moderator
5.56
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Breacher,

What you are saying does have some merit if you are using standard ball type ammunition. However, when you start designing the ammunition for top performance and start coming out of the lawyer proof specifications you get into a different concept.
I will be adding a modification to all of my AR10's. I will be adding an adjustable gas block to each rifle. It will allow me to up the horse power so to speak without beating the rifle to death. The same concept as the FNFAL gas system.

My goal is to have a battle rifle that is a carbine, that will make 1,000 meters. I am VERY close with the ammo design now. With an additional 90 fps the 16" will make it. I will need to change the gas block out first, then all of my AR10's will be able to handle 1,000 meters, they will do 1,000 yards now.

Think of it, one ammo type, accuracy to 1,000 meters from a 16" carbine. That in turn will allow all of the rest of the .308 rifles to do the same as well.

As for the barrel length, remember, each system is not the same. What does matter is the twist, velocity and the coefficients of the various projectiles.

A 147 gr .308 is not designed to raise hell at 1,000 meters. You have a bullet that will drop subsonic in the 800 meter range depending on velocity.
Cost is the factor, FMJ ball of any caliber is far cheaper to produce than match grade ammo. Hence the military will order the cheapest reliable ammo the can get, FMJ.

If I ever have to defend myself in real life again, I want to have the best advantage I can get. My goal is accurate performing ammo from the muzzle to 1,000 meters.

If you folks get the chance you might want to get a ballistic program, chrono your ammo and see what you really have. Unless you do this, you are guessing as to what your rifle can do at distance.

As an example, a 223/5.56 55gr drops subsonic between 700-800 yards, an 80 gr will make it to 1,100 to 1,200 yards before it drops subsonic with about 2,900 fps at the muzzle.

One thing to remember, if it drops subsonic, it becomes erratic. I have key holed 168BTHP at 1,000 yards. meaning they came in sideways in a competition at Camp Perry. I will never use them again for more than a 600 yard competition.

BTW LOL I prefer to use tracers when I can, but at 1,000 meter targets the darn things burn out at about 800 meters.

5.56

[ 06-26-2013, 01:06 AM: Message edited by: 5.56 ]

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