Originally Posted by
bgreed
4140 has been used for barrel making for years with great success. Nothing wrong with it. Again just gun snobs.
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I believe the M1 barrels were 4140. They did okay.
From everything I've read there is a difference between 4140 and 4150 (of course) and 4150 and 4150CMV:
Note should be made that the steel quoted by the OP was 4150 CMV An examination of the chemical analysis of 4150 per AISI specifications shows that this steel is indeed an easier hardening grade but also that vanadium is not present in the alloy. The confusion in terms of barrel steel is that the correct alloy is not 4150 rather a modified vanadium bearing grade per mil specification. The presence of vanadium acts to slow the response of the steel to heat treatment but also as a grain refiner. This promotes excellent ductilty and a high Kic value.
With this noted buyers should beware that they are not getting what they believe is a premuim barrel steel when in fact the vendor has simply used plain AISI 4150 in place of 4140.
Unless you aim to hold the barrel at a temperature that exceeds the solution temperature for the alloy ie the quenching temperature for a significant period of time, the alloys 4140 and 4150 will behave in a near identical manner. It is virtually impossible to effect the grain structure of the steel at the temperatures found within even a heavily abused weapon. However the following are considerations in the selection of barrel steel
The 4150 CMV alloy will allow more margin for error if an overload condition occurs equally they have a much greater resistance to cracking if a heated barrel is suddenly quenched by seawater, snow, etc. This said M2 barrels have been seen with cracks running the full length following one of the rifling grooves from waves hitting a hot gun
At extreme cold levels the properties of 4150 CMV are desirable if the material is to exposed for significant time periods. It is this cold weather feature that is the primary driver in the material selection.
The selection of essentially a specialized gun steel over a commercial AISI grade is always preferable for a safety critical part. Unless the barrel maker can undertake both chemical and microscopic examination of a "rack grade" steel it is possible that the barrel is manufactured from a coarse grained alloy. This will impact the toughness of the finished part.
Bill Alexander
https://www.m4carbine.net/showthread...l-better/page2
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