What steel alloy for barrels?

[ScottMcc]

Most custom barrels are stainless right? Stainless machines better and I heard holds up to throat erosion better, but stainless has a very low thermal conductivity number. It seems to me that with rapid firing, heat will not spread away from the throat area as fast with stainless, maybe resulting in more throat damage. How well does 4340 chro moly work?

 

[Raythemanroe]

SS is easier to machine and holds up to corrosion better..

 

[shortgrass]

SS is easier to machine ..

Since when?? Stainless is always hand lapped (custom barrels) because of the way it machines, chrome moly,,,,, not always. Shilen doesn't lapp their CM barrels but on request and charges more for that service. What alloy? 4140-4150 seems to be the standard. 4150 meets milspecs. I'd say the engineers have already been all over this, before. No sense in trying to "re-invent the wheel".

 

[butchlambert]

What makes you think that SS has less throat erosion than CM? Why would you worry about a little difference in corrosion unless you do not plan on taking care of your equip?

 

[Hal]

If there was a better steel, the barrel maker would be using it. As long a the price was in reason.

Hal

 

[Steve Blair]

If there was a better steel, the barrel maker would be using it. As long a the price was in reason.

Hal

[br]
Barrel makers use different steels for several reasons. If you are shooting in sub-zero temperatures, don't use stainless steel. Standard military barrels are often ORD 4350, a chrome-molybdenum-vanadium steel that is tough as hell but hard to machine. It is the steel of choice for cold hammer forged barrels because the bore work hardens to a high surface hardness. 416R, commonly used for stainless barrels (but not all), is free machining and produces excellent surface finishes in the typical material condition of 28-32 RC. There are a lot of factors that influence the choice of one steel over another for barrel making and cost is not necessarily the largest.

 

[Lazydays]

Most custom barrels are stainless right? Stainless machines better and I heard holds up to throat erosion better, but stainless has a very low thermal conductivity number. It seems to me that with rapid firing, heat will not spread away from the throat area as fast with stainless, maybe resulting in more throat damage. How well does 4340 chro moly work?

most folks are using a propietary grade of 416 stainless steel, and the idea that it machines better than a good certified lot of chrome moly is just not so. One is much tougher than the other, but with the right tools will cut just as well. In the machine shop world it's common knowledge that carbon steel is easier to machine super accurately. I used to gun drill 410, 416, and 420 SS steels on a regular basis, and none are fun. Yet I have done the same with 4***, 6***, and 8*** without any real problems with the correct grind on the drills. A2 and S5 and S7 are you really starting to see a problem. On the otherhand 17PH4 rearc melt and 18-5 SS steels are a bitch on a good day!! In spades! Yet done right 17PH4 cuts well, but will make a Pratt Whitney work a lot harder than I like. A prehardened bar of 4150 or 4350 cuts like a dream come true, and seriously holds good deminsions, but you just have to learn that part of the game. Baldwin sells a very similar steel to 17PH-4 (they call it MR-10) that comes in a pretreat form. Stuff is very tough to machine, and is about all a Bridgeport can handle. Yet the finish and deminsions come out very well in it. But on the otherhand it cuts better than generic 17ph4 that came from who knows who.

The trick to getting a good piece of steel that cuts and heat treats well is to order in a certified lot from the start. I've just never seen a certified lot from any domestic supplier that didn't turn out well. And I've ordered in hundreds of certified lots ovr the years. Yet if somebody were to ask me right now what the finest maching shaft material I've even used, I'd instantly tell them that it came from Timken and was in 52100. Material is very strait, and cuts like butter.
gary

 

[Lazydays]

SS is easier to machine ..

Since when?? Stainless is always hand lapped (custom barrels) because of the way it machines, chrome moly,,,,, not always. Shilen doesn't lapp their CM barrels but on request and charges more for that service. What alloy? 4140-4150 seems to be the standard. 4150 meets milspecs. I'd say the engineers have already been all over this, before. No sense in trying to "re-invent the wheel".

You are correct! The real difference between 4140 and 4150 is that one comes in a pretreat state while the other is soft. Yet I never understood why a pretreat blank of 4350 has the same number as a soft blank! The main advantage of the 4150 piece of stock is that it comes in at about 30RC, and is ready to nitride harden if need be. C/M does seem to heat treat very well, but will never get as hard as tool steel unless you put a case on it thru a good nitride process

All 400 series stainless steel will rust, but not as quickly as carbon steels. On the otherhand most 400 series stainless steel lacks the better granular structure that you get out of a good lot of C/M. 400 series stainless seems to hold up to a higher range of heat than C/M, but how much? To give most of us here an idea what it takes to hold up to higher ranges of heat you must start looking at 330 stainless steel and move upwards to 349 SS. That's what you see a lot of inside heat treat furnaces, along with NiChrome steels (very expensive and very tough and hard). 400 series dosn't cut it in that enviorment; yet the heat range is lower than a rifle throat
gary

 

[Lazydays]

If there was a better steel, the barrel maker would be using it. As long a the price was in reason.

Hal

MAR-10 would be the top of the line in my book. Will not rust in deionized water. Will take a good bit of heat, and fantastic wear properties. Plus it strong as all get out. The downside is that it would probably add a $150 to a barrel blank minimum (and nobody's going to show you how to grind the gun drills or what coolant and coolant pressures to use)
gary

 

[Steve Blair]

You are correct! The real difference between 4140 and 4150 is that one comes in a pretreat state while the other is soft. Yet I never understood why a pretreat blank of 4350 has the same number as a soft blank! The main advantage of the 4150 piece of stock is that it comes in at about 30RC, and is ready to nitride harden if need be. C/M does seem to heat treat very well, but will never get as hard as tool steel unless you put a case on it thru a good nitride process

[br]
BS - the difference between the two is carbon content and a higher potential material condition for 4150. Either can be had in any material condition that you wish from the supplier. [br]
Type 416 has both phosphorus and sulfur added for improved machinability. It is commonly used for screw machine parts because of machining ease. I have visited and discussed operations with barrel manufacturers in eight countries utilizing single hook cut rifling, broaching, cold hammer forging and ECM. They used materials ranging from 416 to 4350. Among those using 416, the primary reason cited was machining ease and surface finish.

 

[ScottMcc]

Machine gun barrels are 4150, right? Presumably so they can survive some overheating in combat. But as far as I know, custom target barrels are stainless for the easier machining and better surface finish. So my original question was related to the poor thermal conductivity of stainless. I thought that maybe during rapid fire shooting in a match or varmint hunting, a stainless barrel may be having more throat erosion than a chromo barrel due to heat lingering in the stainless. But this is all irrelevant if chromo steel isn't capable of the highest level of accuracy that stainless is.

 

[ScottMcc]

FYI:

thermal conductivity, btu-in/hr*ft2*°F

carbon steel: 456
stainless 304-316: 106
stainless 430: 150

This means stainless has 1/3 to 1/4 the thermal condutivity of carbon steel, so it will tale 3 to 4 times longer for heat to spread out of the throat area after a shot. I doubt I am the first one to realize this. Maybe stainless is initially more than 4 times better than carbon steel at resisting throat erosion, so it is still better during rapid fire?

 

[treeman]

seems if thermal conductivity was lower the barrel would absorb less heat... just wondering.

 

[Lazydays]

You are correct! The real difference between 4140 and 4150 is that one comes in a pretreat state while the other is soft. Yet I never understood why a pretreat blank of 4350 has the same number as a soft blank! The main advantage of the 4150 piece of stock is that it comes in at about 30RC, and is ready to nitride harden if need be. C/M does seem to heat treat very well, but will never get as hard as tool steel unless you put a case on it thru a good nitride process

[br]
BS - the difference between the two is carbon content and a higher potential material condition for 4150. Either can be had in any material condition that you wish from the supplier. [br]
Type 416 has both phosphorus and sulfur added for improved machinability. It is commonly used for screw machine parts because of machining ease. I have visited and discussed operations with barrel manufacturers in eight countries utilizing single hook cut rifling, broaching, cold hammer forging and ECM. They used materials ranging from 416 to 4350. Among those using 416, the primary reason cited was machining ease and surface finish.

not what your supplier will tell you. The steels are somewhat similar, but in steel sales 4150 is almost always prehardened. To be exact, I cannot ever remember seeing or even being offered 4150 in a soft state. I used to buy 4140 and 4150 by the flat bed truck loads. I will not argue with you about the carbon content, as I don't have the data handy. But the two steels are very close to each other, but not interchangeable. 4150 also goes by several trade names, and if you pin down a supplier he will admit that they are the samething as 4150 (Versalloy, Nicor, etc)

You can order 416, 410, and 420 with modified amounts of sulphur added to it. This is fairly common practice with the latter two in mold making. It does make it machine easier, but creates other problems later in some cases.
gary

 

[Lazydays]

Machine gun barrels are 4150, right? Presumably so they can survive some overheating in combat. But as far as I know, custom target barrels are stainless for the easier machining and better surface finish. So my original question was related to the poor thermal conductivity of stainless. I thought that maybe during rapid fire shooting in a match or varmint hunting, a stainless barrel may be having more throat erosion than a chromo barrel due to heat lingering in the stainless. But this is all irrelevant if chromo steel isn't capable of the highest level of accuracy that stainless is.

don't think anybody ever said that. I would think it would be something like 4350, 4360, or maybe 4340 C/M steel, and probably pre hardened. (saves time and money). I have no idea what machine gun barrels are made of. Never saw one being machined, except for a couple photos of Krieger cutting M2 barrels.
gary

 

[Lazydays]

FYI:

thermal conductivity, btu-in/hr*ft2*°F

carbon steel: 456
stainless 304-316: 106
stainless 430: 150

This means stainless has 1/3 to 1/4 the thermal condutivity of carbon steel, so it will tale 3 to 4 times longer for heat to spread out of the throat area after a shot. I doubt I am the first one to realize this. Maybe stainless is initially more than 4 times better than carbon steel at resisting throat erosion, so it is still better during rapid fire?

not a flame or anything, but I'm just kinda courious as to where you found the data. Can you post a link of somekind? Or if it's in the Machinest Handbook can you give a page number? Be an interesting read.
gary

 

[butchlambert]

So what is this thread about? I don't see our barrel makers changing steel or alloy in the foreseeable future.

 

[ScottMcc]

I searched on 'thermal conductivity of steels' initially, and of course found too much.. Here is one of the better lists I found:

http://www.engineersedge.com/properties_of_metals.htm

That list uses different units, but it still shows the same 1/3 to 1/4 ratio. The most useful data came from the Watlow Heaters Engineering Guide. It's data was tabulated specifically to show the properties of metals for heat transfer from heating elements, and was the source for what I listed. These properties are not news to me, I am an engineer with a career-long emphisis on hi temp metallurgy and welding. I brought it up here because this is the smartest shooting forum I have encountered, so I thought someone might have considered the low thermal properties of stainless as it might relate to throat erosion.

 

[shortgrass]

So what is this thread about? I don't see our barrel makers changing steel or alloy in the foreseeable future.

This thread is about "jerkin' conclusions out of thin air", Butch! I'm not an engineer,, just an old, dumb a$$ job shop machinist. I've never rifled a barrel, either. But, every barrel maker I've had he opportunity to visit with has stressed that Stainless Barrels must be hand lapped, because of the way stainless machines. Most custom barrel makers seem to go ahead and hand lap the ones they make out of CM, also. There is at least one (Shilen) who will give you the choice of hand lapped or not, in their CM line. I think most who shoot competition choose stainless either , #1 that's the only choice their barrel maker of choice offers, or #2 because the throat in a stainless seems to hold up longer than CM, #3 they know CM isn't very forgiving to the effects of corrosion (pitting, which can happen in a matter of hours). I think every barrel maker already has their "blend" pretty well down and they're not about to change it now without some real, hard core data to back up such a change. And, their all just too darned busy right now to be "experimenting" with steel. They need every machine they've got running , just to supply current demand. "If it ain't broke,,, don't fix it!". I am much more inclined to take the word of those who actually make barrels (put cutting tool to steel) than to wander of into theory

 

[butchlambert]

Shortgrass,
I'll have to differ with you on throat erosion and if you care for your barrels, corrosion is not a problem. My experience shows no difference between the 2 as accurate shooters. I have heard these things said, but no actual proof of this.