<span style="font-weight: bold">Barrels steel difference's:</span>
416 stainless barrel
416 R stainless barrel
OBERMEYER RIFLED BARRELS
Quality Rifle Barrels Since 1962
23122 - 60th Street
Bristol, Wisconsin 53104
--------------------------------------------------------------------------------
Barrel Steels
A Note on Steel
During the manufacturing process, barrel-quality steel is carefully controlled and inspected to
ensure the material structure is correct for rifle barrel use. There are two basic steel options
available: stainless steel and chromium-molybdenum alloy steel. Stainless steels are special,
gun-barrel quality grades of Carpenter or Crucible 416. Our suppliers of chrome-moly steels have
changed as the American steel industry continues to suffer bankruptcies and closures due to
competition from cheap, imported steels. (For more information regarding the impact of the steel
industry crisis on American manufacturing and national security, see "Blood and Iron Pyrite" by
Eric J. Obermeyer in Chronicles: A Magazine of American Culture, Vol. 28 No. 4, April 2004, pages
51-53.) This has resulted in a situation where high-quality specialty grades of steel are becoming
harder to obtain and minimum order quantities are now about 10 times larger. This special quality
steel is not imported and two mills in Europe have turned me down because small quantities of
steel are not worth their efforts. A number of custom barrel-makers are working together to pool
resources in order to have the ability to place combined orders large enough to meet the quantity
threshold. Standard raw chrome-moly blank diameters now will be 1-1/4" and 1-3/8", although this
is subject to change with availability from steel suppliers. One of the former chrome-moly
standards, 1-5/16" bar diameter, may be available in remnant quantities subject to stock on hand.
The normal raw diameter for stainless steel blanks is 1-5/16".
Each basic type of barrel-quality steel has advantages, depending on the application. Chrome-moly
barrels develop a fine-line erosion pattern in the throat, which I compare to fine gravel in a
stream. With bare bullets, this can cause greater variations in velocity, due to drag exerted on
the bullet in the throat region. This situation may result in an increase in the vertical dispersion
of the shots that is particularly noticeable at longer ranges. The testing I have performed in my
target rifles leads me to believe that molybdenum disulfide coating on bullets, when properly
applied, has a mitigating effect in this regard. (Each of the several chrome-moly match rifle barrels
in .260 Remington that I have used in conjunction with moly-coated bullets has exceeded 6000
rounds of accurate life.) Also, chrome-moly having 40 to 50 points of carbon may harden in the
throat area from use. This can cause damage to your chamber reamer if you try to set such a
barrel back. On the other hand, chrome-moly takes more abuse from peening or abrasion, and this
is a big advantage where field use is rough. It also tends to be stronger in cold-weather
environments, such as might be encountered while hunting in Alaska, where the temperature is
often below zero.
Barrel-quality stainless steel is usually identified as type 416R or 416RS, and it has approximately
half the sulfur content of common, warehouse-grade 416. Stainless steel barrels will not harden in
the throat area, which provides a big advantage for target shooters who plan to set their barrels
back when the throats wear. The erosion pattern of stainless steel looks like a dried-up mud
puddle, having large flats with fracture lines. This reduces the drag on the bullet, so there is less
tendency for vertical stringing at long ranges. Sometimes, after a lot of use, a large piece may pop
out from the throat of a stainless steel barrel, causing it to suddenly lose accuracy. Stainless steel
will also scratch or peen easier than chrome-moly barrel steel of comparable hardness. In
applications involving military weapons, this sort of material behavior would present a real
problem, which is why chrome-moly is generally used. Stainless steel also has less ductility than
chrome-moly, particularly when the ambient temperature approaches zero. Thus, a featherweight
stainless steel barrel would not be the best choice for hunting in Alaska. Also, contrary to some
people's notions, stainless steel is not hard to machine; it's actually easier than chrome-moly.
The type of steel used has a significant impact on the price of a barrel, since stainless steel costs
approximately four times more than chrome-moly. In addition to the cost differential associated
with the material in the barrel itself and with the material removed during the manufacturing
process, there are additional costs due to drops resulting from having to purchase bars of certain
lengths, which may not allow for full, end-to-end usage. Furthermore, the relatively high cost of
stainless steel (and the tremendous difficulty of purchasing any barrel-quality steel in smaller
quantities) forces the small manufacturer to tie up substantial amounts of money in inventory.
Nevertheless, the greater cost of stainless steel does not automatically imply that it is a better
material than chrome-moly for a given application.
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<span style="font-weight: bold">Lower's difference's?:</span>
solid billet of 6061-T6 aluminum
7175-t73 Aluminum (forged)
""I'm thinking about building an AR in .308 Win so I am glad to have found this forum. I'm also an engineer so I analyze everything then analyze my analysis. Here is some information I have gathered about manufacturers and materials.
MMS = Mega Machine Shop
They use 7075-T6 Aluminum and don't seem to make a .308 version of their uppers or lowers.
LAR = LAR Manufacturing
They use 7075-T6 Aluminum and don't seem to make a .308 version of their uppers or lowers.
LMT = Lewis Machine Tool Company
They make a .308, but their website does not mention the Aluminum alloy they use. The OP listed them as the source for Bushmaster rifles and Bushmaster says theirs are 7075-T6 Aluminum.
CMT = Stag Arms (?)
They use 7075-T6 Aluminum and don't seem to make a .308 version of their uppers or lowers.
DPMS = Panther Arms
They make a .308 using 6061-T6 Aluminum.
Armalite
They make a .308 using 7175-T73 Aluminum.
POF = Patriot Ordinance Factory
They make a .308 using 7075-T6 Aluminum.
About Aluminum alloys:
6000 series are alloyed with magnesium and silicon, are easy to machine, and can be precipitation-hardened, but not to the high strengths that 7000 can reach.
7000 series are alloyed with zinc, and can be precipitation hardened to the highest strengths of any aluminium alloy.
Temper designations
-T6 Solution heat treated and artificially aged
-T7 Solution heat treated and stabilized
6061-T6 alloy has good mechanical properties and has good weldability. It has a yield strength (Fy) of at least 35,000 psi. Weldability is why it is used in aircraft structures, automotive parts and bicycle frames.
7075 is strong but has less corrosion resistance than other AL alloys. It is more expensive than 6061.
7075-T6 has a yield strength (Fy) of 54,000 - 67,000 psi. This is why receiver manufacturers say their 7075-T6 parts are stronger than others. 7075-T6 is slightly more susceptible to corrosion due to prolonged exposure to water or water vapor. This has the effect of reducing the strength slightly, but the average AR user is not likely to experience this unless your weapon spends the winter at the bottom of a pond.
7075-T73 has a yield strength (Fy) of 51,000 - 54,000 psi. This difference is due to a slightly different tempering process. It results in a 7075 alloy that is nearly as strong and has better corrosion resistance than -T6. That's probably why Armalite uses it.""
=============================================================================================================================
416 stainless barrel
416 R stainless barrel
OBERMEYER RIFLED BARRELS
Quality Rifle Barrels Since 1962
23122 - 60th Street
Bristol, Wisconsin 53104
--------------------------------------------------------------------------------
Barrel Steels
A Note on Steel
During the manufacturing process, barrel-quality steel is carefully controlled and inspected to
ensure the material structure is correct for rifle barrel use. There are two basic steel options
available: stainless steel and chromium-molybdenum alloy steel. Stainless steels are special,
gun-barrel quality grades of Carpenter or Crucible 416. Our suppliers of chrome-moly steels have
changed as the American steel industry continues to suffer bankruptcies and closures due to
competition from cheap, imported steels. (For more information regarding the impact of the steel
industry crisis on American manufacturing and national security, see "Blood and Iron Pyrite" by
Eric J. Obermeyer in Chronicles: A Magazine of American Culture, Vol. 28 No. 4, April 2004, pages
51-53.) This has resulted in a situation where high-quality specialty grades of steel are becoming
harder to obtain and minimum order quantities are now about 10 times larger. This special quality
steel is not imported and two mills in Europe have turned me down because small quantities of
steel are not worth their efforts. A number of custom barrel-makers are working together to pool
resources in order to have the ability to place combined orders large enough to meet the quantity
threshold. Standard raw chrome-moly blank diameters now will be 1-1/4" and 1-3/8", although this
is subject to change with availability from steel suppliers. One of the former chrome-moly
standards, 1-5/16" bar diameter, may be available in remnant quantities subject to stock on hand.
The normal raw diameter for stainless steel blanks is 1-5/16".
Each basic type of barrel-quality steel has advantages, depending on the application. Chrome-moly
barrels develop a fine-line erosion pattern in the throat, which I compare to fine gravel in a
stream. With bare bullets, this can cause greater variations in velocity, due to drag exerted on
the bullet in the throat region. This situation may result in an increase in the vertical dispersion
of the shots that is particularly noticeable at longer ranges. The testing I have performed in my
target rifles leads me to believe that molybdenum disulfide coating on bullets, when properly
applied, has a mitigating effect in this regard. (Each of the several chrome-moly match rifle barrels
in .260 Remington that I have used in conjunction with moly-coated bullets has exceeded 6000
rounds of accurate life.) Also, chrome-moly having 40 to 50 points of carbon may harden in the
throat area from use. This can cause damage to your chamber reamer if you try to set such a
barrel back. On the other hand, chrome-moly takes more abuse from peening or abrasion, and this
is a big advantage where field use is rough. It also tends to be stronger in cold-weather
environments, such as might be encountered while hunting in Alaska, where the temperature is
often below zero.
Barrel-quality stainless steel is usually identified as type 416R or 416RS, and it has approximately
half the sulfur content of common, warehouse-grade 416. Stainless steel barrels will not harden in
the throat area, which provides a big advantage for target shooters who plan to set their barrels
back when the throats wear. The erosion pattern of stainless steel looks like a dried-up mud
puddle, having large flats with fracture lines. This reduces the drag on the bullet, so there is less
tendency for vertical stringing at long ranges. Sometimes, after a lot of use, a large piece may pop
out from the throat of a stainless steel barrel, causing it to suddenly lose accuracy. Stainless steel
will also scratch or peen easier than chrome-moly barrel steel of comparable hardness. In
applications involving military weapons, this sort of material behavior would present a real
problem, which is why chrome-moly is generally used. Stainless steel also has less ductility than
chrome-moly, particularly when the ambient temperature approaches zero. Thus, a featherweight
stainless steel barrel would not be the best choice for hunting in Alaska. Also, contrary to some
people's notions, stainless steel is not hard to machine; it's actually easier than chrome-moly.
The type of steel used has a significant impact on the price of a barrel, since stainless steel costs
approximately four times more than chrome-moly. In addition to the cost differential associated
with the material in the barrel itself and with the material removed during the manufacturing
process, there are additional costs due to drops resulting from having to purchase bars of certain
lengths, which may not allow for full, end-to-end usage. Furthermore, the relatively high cost of
stainless steel (and the tremendous difficulty of purchasing any barrel-quality steel in smaller
quantities) forces the small manufacturer to tie up substantial amounts of money in inventory.
Nevertheless, the greater cost of stainless steel does not automatically imply that it is a better
material than chrome-moly for a given application.
============================================================================================================================
<span style="font-weight: bold">Lower's difference's?:</span>
solid billet of 6061-T6 aluminum
7175-t73 Aluminum (forged)
""I'm thinking about building an AR in .308 Win so I am glad to have found this forum. I'm also an engineer so I analyze everything then analyze my analysis. Here is some information I have gathered about manufacturers and materials.
MMS = Mega Machine Shop
They use 7075-T6 Aluminum and don't seem to make a .308 version of their uppers or lowers.
LAR = LAR Manufacturing
They use 7075-T6 Aluminum and don't seem to make a .308 version of their uppers or lowers.
LMT = Lewis Machine Tool Company
They make a .308, but their website does not mention the Aluminum alloy they use. The OP listed them as the source for Bushmaster rifles and Bushmaster says theirs are 7075-T6 Aluminum.
CMT = Stag Arms (?)
They use 7075-T6 Aluminum and don't seem to make a .308 version of their uppers or lowers.
DPMS = Panther Arms
They make a .308 using 6061-T6 Aluminum.
Armalite
They make a .308 using 7175-T73 Aluminum.
POF = Patriot Ordinance Factory
They make a .308 using 7075-T6 Aluminum.
About Aluminum alloys:
6000 series are alloyed with magnesium and silicon, are easy to machine, and can be precipitation-hardened, but not to the high strengths that 7000 can reach.
7000 series are alloyed with zinc, and can be precipitation hardened to the highest strengths of any aluminium alloy.
Temper designations
-T6 Solution heat treated and artificially aged
-T7 Solution heat treated and stabilized
6061-T6 alloy has good mechanical properties and has good weldability. It has a yield strength (Fy) of at least 35,000 psi. Weldability is why it is used in aircraft structures, automotive parts and bicycle frames.
7075 is strong but has less corrosion resistance than other AL alloys. It is more expensive than 6061.
7075-T6 has a yield strength (Fy) of 54,000 - 67,000 psi. This is why receiver manufacturers say their 7075-T6 parts are stronger than others. 7075-T6 is slightly more susceptible to corrosion due to prolonged exposure to water or water vapor. This has the effect of reducing the strength slightly, but the average AR user is not likely to experience this unless your weapon spends the winter at the bottom of a pond.
7075-T73 has a yield strength (Fy) of 51,000 - 54,000 psi. This difference is due to a slightly different tempering process. It results in a 7075 alloy that is nearly as strong and has better corrosion resistance than -T6. That's probably why Armalite uses it.""
=============================================================================================================================
