Impulse Buy AR 10 now lots of ???
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Plainsman
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http://www.ar15.com/forums/t_3_16/567875_308_and_7_62x51.html
from ar10 faq
9. Is the chamber on an AR10 .308 or 7.62?
From Armalite: All of our AR-10 .308's are NATO chambered and will accept both 7.62 and .308 ammo. The AR-10 can shoot 308 OR 7.62 NATO.
The difference between .308 and 7.62 is chamber size, slight pressure differences due to powder burn rates, not external case size. Both cases will have the same external dimensions while the .308 has a slightly higher pressure 60Kish vice 50-55 CUP psi for NATO**. NOTE: This is OPPOSITE from the 5.56/.223 rule of thumb. The NATO chambers have greater tolerances to help with reliable functioning of military ammo. The NATO chamber is ever so slightly longer at .013". This is significant in that for reloading purposes, 308 brass will stretch more in a military chamber upon firing, thereby reducing the life of the brass and possibly promoting case head separation. But that additional chamber length will allow a round to chamber in an incredibly dirty weapon, which is a requirement for military applications. Also be aware this is why mil NATO brass is thicker vice 308 commercial brass. You will also see this "thicker brass fact" posted about 5.56/.223 brass which is a fallacy.
**As a side note the reason the pressure issue is confusing is becuase the military measured 7.62 NATO chamber pressure (PSI) via CUP (in the 40s) vice the normal commercial rating of PSI measured (now) with electronic means. You will see many cling to the 50-55K PSI figure for 7.62 Nato becuase that is what the old Army TMs have in them. Since there is no conversion for the CUP measurement to the newer electronic measured PSI, they are two different numbers i.e no direct comparison. Many people will assume the CUP PSI is the same as SAAMI/Commercial PSI. It is not. Commercial PSI is derived from the direct pressure in the chamber through electronic means (piezo transducer or strain gauges). CUP is a crush measurement of a copper slug that has been fired, again not the same test.
That means any newer weapon will be able to fire 308 Commercial ammo as manfs would not let them out the door if they could not, due to liability. Don't believe me, run the numbers/powders in any internal ballistics calculator and they will all be close to the 60K mark. BTW the proof load for the 308 commercial is 75K PSI, so don't worry about the 60K.
GO GAGE CHAMBER SPEC INFORMATION (TOLERANCES FOR GOOD-TO-GO CHAMBERS)
•AR-10 NATO – 1.633-1.638 (stainless steel, chrome moly, and chrome lined barrels) "
308 Winchester (SAAMI) Headspace
GO - 1.6300"
NOGO - 1.6340"
FIELD - 1.6380"
7.62 NATO (Military) Headspace
GO - 1.6350"
NOGO - 1.6405"
FIELD - 1.6455"
Note that the military chamber would fail a NO GO check with a SAAMI gauge, but pass a FIELD check using the proper military gauges.
from ar10 faq
9. Is the chamber on an AR10 .308 or 7.62?
From Armalite: All of our AR-10 .308's are NATO chambered and will accept both 7.62 and .308 ammo. The AR-10 can shoot 308 OR 7.62 NATO.
The difference between .308 and 7.62 is chamber size, slight pressure differences due to powder burn rates, not external case size. Both cases will have the same external dimensions while the .308 has a slightly higher pressure 60Kish vice 50-55 CUP psi for NATO**. NOTE: This is OPPOSITE from the 5.56/.223 rule of thumb. The NATO chambers have greater tolerances to help with reliable functioning of military ammo. The NATO chamber is ever so slightly longer at .013". This is significant in that for reloading purposes, 308 brass will stretch more in a military chamber upon firing, thereby reducing the life of the brass and possibly promoting case head separation. But that additional chamber length will allow a round to chamber in an incredibly dirty weapon, which is a requirement for military applications. Also be aware this is why mil NATO brass is thicker vice 308 commercial brass. You will also see this "thicker brass fact" posted about 5.56/.223 brass which is a fallacy.
**As a side note the reason the pressure issue is confusing is becuase the military measured 7.62 NATO chamber pressure (PSI) via CUP (in the 40s) vice the normal commercial rating of PSI measured (now) with electronic means. You will see many cling to the 50-55K PSI figure for 7.62 Nato becuase that is what the old Army TMs have in them. Since there is no conversion for the CUP measurement to the newer electronic measured PSI, they are two different numbers i.e no direct comparison. Many people will assume the CUP PSI is the same as SAAMI/Commercial PSI. It is not. Commercial PSI is derived from the direct pressure in the chamber through electronic means (piezo transducer or strain gauges). CUP is a crush measurement of a copper slug that has been fired, again not the same test.
That means any newer weapon will be able to fire 308 Commercial ammo as manfs would not let them out the door if they could not, due to liability. Don't believe me, run the numbers/powders in any internal ballistics calculator and they will all be close to the 60K mark. BTW the proof load for the 308 commercial is 75K PSI, so don't worry about the 60K.
GO GAGE CHAMBER SPEC INFORMATION (TOLERANCES FOR GOOD-TO-GO CHAMBERS)
•AR-10 NATO – 1.633-1.638 (stainless steel, chrome moly, and chrome lined barrels) "
308 Winchester (SAAMI) Headspace
GO - 1.6300"
NOGO - 1.6340"
FIELD - 1.6380"
7.62 NATO (Military) Headspace
GO - 1.6350"
NOGO - 1.6405"
FIELD - 1.6455"
Note that the military chamber would fail a NO GO check with a SAAMI gauge, but pass a FIELD check using the proper military gauges.
Last edited:
kimberkid
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Scopes are a personal thing ... That said I've never been disappointed in Leupold as an all around general scope I like the 4-12x40 ... they make a duplex reticle with 2 dots on the bottom leg which I've used for ranging ... It runs about $325 and IMHO nothing in that price range compares ... Other scopes of twice the price have disappointed me so I don't buy anything but Leupolds anymore.
As to ammo, I have a Stoner SR-25 Match with a 24" barrel and 1 in 11.25 twist and a SiG SSG-3000 with a 24" 1 in 11 twist ... Both group around .6 MOA with Federal GMM ... I get similar results with my load of a Sierra 168 HPBT Match bullet with 41.8 grains of BLC2 out to 300 yards which is the furthest I've shot them ... I don't know what the effect of a 16" barrel would be on that load.
A edit to add;
My brass is Lake City and I use standard large rifle primers
My ar10 experience with a 1-10 twist
if you go with LC brass, assume it is machine gun fired, and get a small base sizing die (YMMV, but i had to in order to chamber LC brass)
Bullets: my gun likes 168 amax, 165 game king, but i have only shot about 300 rds through it so i have not done extensive testing
Brass: LC works well, is cheap and i have gotten 7 loads with some with no failure, winchester brass i have also picked up and got some good groups with, only fired it once though
Scope: that is all what you want, i have a vortex viper pst 4x16 First focal plane on mine i really like but that might be heavier or larger than you want for your purpose. That is a nice rifle though, i want one but she who must be obeyed said no
Sent from my SM-G900V using Tapatalk
if you go with LC brass, assume it is machine gun fired, and get a small base sizing die (YMMV, but i had to in order to chamber LC brass)
Bullets: my gun likes 168 amax, 165 game king, but i have only shot about 300 rds through it so i have not done extensive testing
Brass: LC works well, is cheap and i have gotten 7 loads with some with no failure, winchester brass i have also picked up and got some good groups with, only fired it once though
Scope: that is all what you want, i have a vortex viper pst 4x16 First focal plane on mine i really like but that might be heavier or larger than you want for your purpose. That is a nice rifle though, i want one but she who must be obeyed said no
Sent from my SM-G900V using Tapatalk
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