4140, 4150, 316, 17-4, 6061, 7075-T6 — What is the significance of these numbers? No, they’re not winning lottery numbers. These are all designations for metals commonly used in firearm and barrel construction. 4140 and 4150 are carbon steels, with 4150 often used in mil-spec AR15 barrels. 316 and 17-4 are grades of stainless steel. 316 is “marine grade” stainless, while 17-4 has 17% chromium and 4% nickel. 17-4 is a harder steel used in barrels and receivers. 6061 and 7075-T6 are aluminum alloys. 6061 is “aircraft grade” aluminum, often used for rings and trigger guards, while 7075-T6 is a much stronger, heat-treated aluminum commonly used in AR15 uppers.

You can learn about all these metals (and more) in the online archives of RifleShooter magazine.

Written by Patrick Sweeney, RifleShooter’s Guide to Gun Metal summarizes the primary types of steel and aluminum used in gun and barrel construction. Sweeney explains the nomenclature used to define metal types, and he outlines the salient properties of various steel and aluminum alloys. This is a useful resource for anyone selecting components or building rifles. We recommend you print out the page, or at least bookmark it.

Metals by the Number
The number system for steel classification came from the auto industry. Sweeney explains: “The Society of Automotive Engineers uses a simple designating system, the four numbers you see bandied about in gun articles. Numbers such as 1060, 4140 or 5150 all designate how much of what [elements are] in them. The first number is what class—carbon, nickel, chromium, and so forth. The next three numbers [list other elements in the alloy]. 4140, also known as ordnance steel, was one of the early high-alloy steels. It has about 1 percent chromium, 0.25 percent molybdenum, 0.4 percent carbon, 1 percent manganese, around 0.2 percent silicon and no more than 0.035 percent phosphorus and no more than 0.04 percent sulphur. That leaves most of it, 94.25 percent, iron.”

Aluminum Alloys
Numbers are also used to differentiate different types of aluminum alloys. Sweeny writes: “Aluminum is used in firearms in two alloys: 7075 and 6061. 6061 is commonly referred to as ‘aircraft aluminum’ and has trace amounts of silicon, copper, manganese, molybdenum and zinc. 7075 is a much stronger alloy and has markedly larger amounts of copper, manganese, chromium and zinc.” 7075 Aluminum has significantly better corrosion resistance, and that’s why it is used for AR receivers. The “T6″ you often see appended to 7075 refers to a heat-treating process.

Aluminum (or “Aluminium” in the UK) is a chemical element in the boron group with symbol Al and atomic number 13. It is a silvery-white, soft, nonmagnetic, ductile metal. Aluminum is the third most abundant element, and the most abundant metal, in the Earth’s crust. (Wikipedia)

To learn more about the metals used in your firearms’ barrels, rings, receivers, and internal parts, read Sweeney’s article in RifleShooterMag.com. Taking the time to read the article from start to finish will expand your knowledge of metal properties and how metals are chosen by manufacturers and gunsmiths. CLICK to Read Guide to Gun Metal.

In all seriousness, this is impressive Mil-Spec FMJ ammunition right off the production line. The 62-grain green-tipped bullets feature a hardened steel penetrator core. The boxer-primed cases are fully reloadable (though the miltary primer crimps would have to be removed). The ammo is delivered in a heavy-duty steel drum, with steel clamp-on lid with rubber seal. Each container is plastic-lined and packed (from the factory) with dessicant pouches for long term storage.

NOTE: In some jurisdictions there may be restrictions on this product (based on the quantity of rounds or other factors). Check your local laws and regulations.

Brack Wilson of Patriot Cases explains: “FINALLY, after hundreds of requests, our new AR case is available for purchase online at PatriotCases.net This is an incredible deal at only $59.99, and we are offering a special discount for purchases through end of day Monday (April 8, 2013). Enter discount code Facebook at checkout.”

Dennis Santiago tells us: “If you have one of these genetically modified AR-15s set up in 21st Century shooting configuration, this is the case for you. This is perfect for your 3-gun machine…. Friend Brack Wilson just started making them and they went up on his company’s shopping cart today. It’s a solid, lockable design that uses mil-spec heavy foam. They’re on introductory special this weekend so now’s the time to grab one. Enter discount code “Facebook” at checkout and it will deduct $10 from the total cost (so your net cost is $49.99). I think this is the deal of the weekend.”

Dennis hopes that Patriot will produce another version for High Power Shooters: “For you high power guys, I’ve asked Brack to consider making a version with cutouts for the Service Rifle AR-15 with magazine cut outs for one of those Creedmoor mag pouches, a couple of more 20-rd mags (sled + sighter mags), an ECI, a sling, a scorebook. Our kind of stuff. It’d be nice to have a proper hard case with the right cutouts for these guns. It’ll make them safer for transport going to matches.”