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Barrel Steel Differences
There is a wide selection of barrels out there today with prices that vary widely. This is true not only for the AR platform but other rifles as well. It can sometimes be difficult to wade through the specifications, so we have put together a brief summary of the common steel grades used to manufacture barrels and their best uses. In general, the old axiom of “you get what you pay for” tends to hold true in this arena.
When determining the best barrel for you it comes down to 3 basic criteria.
Carbon .5% or .4%
The ‘41’ in this value indicates the AISI-SAE numbering for Chromium-Molybdenum alloy (chrome-moly) and contain between .5% and .95% chromium and .12% to .30% Molybdenum. The second part of the number refers to the amount of carbon in tenths of a percent. A 4140 steel has .4% carbon while a 4150 has .5% carbon. The extra carbon in 4150 makes is tougher with more heat resistance, but it is more difficult to work and machine.
Metal has a crystalline structure and the small Carbon atoms find their way in-between the iron atoms when alloys are heated, strengthening the crystalline structure. By quickly cooling the heated metal the Carbon atoms are frozen in place resulting in a much stronger and harder metal. As the name implies Chrome Moly steel has chrome as part of its alloy; about 1%. This is not enough to inhibit rust, but it does increase the tensile strength when combined with Carbon to around 100,000 psi and increases the yield strength in the range of 75,000 psi after proper heat treating.
A 4150 steel is a mil-spec material for barrels while a 4140 steel is not. It is, however, cheaper to buy 4140 steel so you will see some barrels made from this material. Will they work – yes, will they last as many rounds or stand up to high heat like 4150 will – no.
Stainless Steel 416 & 416R
Stainless Steel is designed for corrosion resistance with a much higher content of Chrome than regular steels. This Chromium forms a passive film of Chromium Oxide about the outer surface which prevents corrosion by blocking oxygen diffusion at the surface and preventing its spread into the internal structure of the metal. Tensile strength of 416 Stainless falls into the 75,000 psi range and its yield is 40,000 psi which is significantly under 4150 steel. What is loses in hardness it gain in machinability. The structure of 416 lends itself to machining much better with a vastly improved surface finish. This, in turn, allows it to take a better cut in the machining process creating higher definition rifling, crowns, and chambers. 416-R stainless has reduced barrel life compared to 4150 but will stay more accurate over its usable life.
One thing to watch for is barrels made with 416 stainless vs 416R stainless. Common 416 gets brittle at freezing temperatures while 416R is formulated to function in arctic conditions down to -40 F.
At the end of the day if you want a barrel to stand up to wear and tear and last as long as possible go with 4150. If you are shooting competitively, either in competitions or simply in competition with yourself, go with 416R. You will find cheap barrels on the internet and be tempted to ‘get a good deal’, however, I would strongly suggest you research the how the barrels are made and of what material. At Right To Bear, Arms Co we only use barrels made from 4150 or 416R steel. In addition, our barrels get a QPQ salt bath nitrocarburization resulting in a stronger, longer lasting surface finish.