Why is 4150 steel better?

[Whytep38]

Interesting to note that, despite the fact that 4140 is agreed by all to be the weaker steel when rapidly heated under sustained firing, there does not appear to be a single maker that sells a 4140 barrel that also MPIs and HPTs every single sample of their barrels.

I've been told by people who take old M-1 barrels and cut them up for other uses that M-1 barrels are 4140 steel. During WWII, was every M-1 barrel MPI'd and HPT'd?

I ask because I don't know. Given the production technology and production demands at the time, I suspect not. But it's possible. Since this point has now been brought up, it would be useful to know. Because if M-1 barrels were 4140 steel and not every barrel was MPI'd and/or HPT'd, I'm not sure why they'd be rugged enough to help win WWII and yet inadequate for civilian use.

[greentips]

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.

Bill Alexander

How does the 416 SS used by most "custom" barrels behave in cold temperature and sudden quenching, in comparison to 4150 CMV?

[Yojimbo]

I've been told by people who take old M-1 barrels and cut them up for other uses that M-1 barrels are 4140 steel. During WWII, was every M-1 barrel MPI'd and HPT'd?

I ask because I don't know. Given the production technology and production demands at the time, I suspect not. But it's possible. Since this point has now been brought up, it would be useful to know. Because if M-1 barrels were 4140 steel and not every barrel was MPI'd and/or HPT'd, I'm not sure why they'd be rugged enough to help win WWII and yet inadequate for civilian use.

I don't know the real answer to your question but my guess is that M1 barrels were not all HPT and MPI. I'm not sure MPI was even available back then.

I also don't believe anyone is saying that 4140 is inadequate but rather CMV and 4150 spec barrels can do some things better. It's not so much that there's anything wrong with 4140 but rather there are some advantages to be had with using 4150 and CMV instead.

Whether or not these advantages are worth the extra cost is only something the end user can decide.

[Whytep38]

Whether or not these advantages are worth the extra cost is only something the end user can decide.

+1. You've done a better job summing up my position than I have.

[WS6]

I don't know the real answer to your question but my guess is that M1 barrels were not all HPT and MPI. I'm not sure MPI was even available back then.
I also don't believe anyone is saying that 4140 is inadequate but rather CMV and 4150 spec barrels can do some things better. It's not so much that there's anything wrong with 4140 but rather there are some advantages to be had with using 4150 and CMV instead.
Whether or not these advantages are worth the extra cost is only something the end user can decide.

MPI was invented/discovered in the 1920's by William Hoke.

I also feel there are advantages. For the average guy the difference is about the same as whether or not you have a forged or a cast crank shaft in your current daily driver. Do you know which it has? Do you care? Has your DD ever snapped the crankshaft on your daily commute?

Ah! It is for the end user to decide, and the military (who spec'ed it) has decided.

Back to my crankshaft analogy, this reminds me of a special I once saw on a ATV looking military vehicle that the History channel was describing. It showed said ATV in action with vivid commentary about how the tires could shrug off (or rather have run-flat or self-sealing capability) shrapnel, bullet strikes, mines ect. It described just how high/far it could ramp and how deep a stream it could forge through.

Now, do I need THOSE TIRES on MY 4-wheeler? Nah, I bet I dont. Just like you don't need a forged crank in your honda civic 4-door that you use to go to-from work (I have no clue what YOU drive, just an analogy using the collective "you"). However, if my 4-wheeler and I were stationed in an unfriendly place and there were people out there shooting at me and I had a choice you better belive my tires would be the most hardcore, badass, over-engineered slabs of rubber or techno-polymer I could put on my vehicle!

The same holds true for 4150 barrel steel. It may be a little better, JUST a LITTLE, but what is a few dollars, if that, more per barrel when the military can justify it by saying that without this steel, our troops would have a SLIGHT disadvantage in a long firefight. We have all heard the accounts whether in person or on the history channel or wherever about a US position under heavy fire without re-enforcements where the troops fire their weapons to the point to where the barrls glow and droop and whatnot. While I feel it is an exaggeration most of the time, I feel that a superior barrel steel like 4150 vs. 4140 MAY allow another 1-200 rounds to go downrange before the rifling is completely worthless. Who knows, that 1-200 rounds might make the difference.

The US Govt. Feels that it might apparently. Do you as the user need this? That one is up to you. Me? I just think it is a "neat feature", kinda like the low-tension oil rings and short skirt pistons in my daily go-getter.

Im sorry I am a bit light on technical information and chemistry, but I think this sums up the reason/mentality demanding this steel vs. 4140.

Sources:
A lot of people have encouraged me to provide sourcs for any "technical" information given. I have provided such. I would also like to state that this is a lot of my OPINION on why 4150 is spec'ed and I am not trying to pass it off as anything more.

http://www.ndt-ed.org/EducationResou...on/history.htm

http://www.gdls.com/pdf/Stryker_hard_facts.pdf

[DuGaul]

4150 = Higher Thermal Conductivity

It dissipates heat better than chrome-moly, and five times faster than stainless steel.

[30russkie]

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

i am not completely convinced that 4150cv is the correct term for the mill spec steel but it is close.

i think the CV part is because some mg & rifle barrels back in the 70s split open during extended rapid fire tests so the CV was added to the standard 4150.

i think the CV steel barrels do have a slight edge with the heat of extended rapid firing--but i also think it is ever so slight.

some of our allies in the sand-trap had m-70 akm's and we saw them do some pretty heavy extended automatic fire--they had no real problems with their barrels that i could see. nothing burst or melted, their rifles seemed to still shoot pretty tight after the event--- also no chrome lining and i'll bet nothing like 4150 steel or even 4140--


for anything short of running a full-auto range where you have a company of boots firing 100rd belts one behind the other i don't think you will need the CV. don't get me wrong if i can get the CV barrels for reasonable$$ i will but i don't sweat if if i find a good deal on a rifle/upper with 4140 chrome--

[DedEye]

How does 4150 steel compare to the stainless steel used by folks like Larue or Noveske? Larue uses LW-50 Stainless, not sure what Noveske uses. Why do those manufacturers use stainless, more accurate?

Also, my first post in the forum, so hello!

ETA: Seems I found my answer in this thread: http://m4carbine.net/showthread.php?t=756

[C4IGrant]

How does 4150 steel compare to the stainless steel used by folks like Larue or Noveske? Larue uses LW-50 Stainless, not sure what Noveske uses. Why do those manufacturers use stainless, more accurate?

Also, my first post in the forum, so hello!

ETA: Seems I found my answer in this thread: http://m4carbine.net/showthread.php?t=756

Remember that 4150 (by that name) is not equal to the three types of barrel steel that the Military uses.

SS barrels tend to be more accurate. The trade off is longevity. Noveske also has hammer forged, M249 barrels that they call N4 (which are chrome lined).



C4

[DedEye]

Remember that 4150 (by that name) is not equal to the three types of barrel steel that the Military uses.

SS barrels tend to be more accurate. The trade off is longevity. Noveske also has hammer forged, M249 barrels that they call N4 (which are chrome lined).



C4

Thanks C4. I know that the SS barrels drop off in accuracy at the end of their lives, but how much shorter is that lifespan compared to CM barrels?