17-4 PH Stainless cut rifled barrels

[sirrocco]

I am about to have a batch of cut rifled barrels made out of 17-4 Ph stainless steel and was curious as to whether or not you guys shooting over-bore large capacity magnums might be interested in a barrel that would last say 2,500 accurate rounds versus's the 800 or so that one often gets. The 17PH is hardened to about 44RC in comparison to 416R which is about 28RC which is why the barrel life is extended by approx 3 times.
So what do you think, if they prove to be just as accurate as 416 tubes but life is greatly extended would they be of any interest to you overbore boys? ( BTW have no concerns about chambering the harder steel, its not a problem.)

 

[RockZ]

That is very interesting.
As long as they prove accurate over a longer period ,
it all depends upon the cost of the barrels.

 

[sirrocco]

Well thats the idea of using 17-4 Ph, it is significantly more corrosion resistant than 416. In addition to the superior corrosion resistance it is approx 50% stronger than 416 and doesn't have the cold temperature failure issues that 416 has. Krieger for example will not sell a stainless tube in less than a #5 contour for this reason. Lothar Walther barrels use a material that is similar / same and I have had a giood run with those previously but they are button rifles and cannot have gain twist rifling.......... Which brings me to the next point. It makes more sense to have the rifling start almost straight and then progressively sped up to the ultimate twist rate. So for example a 30 cal tube would start out at twist rate of 1-100" and progressively get faster till it ends up in a 1-10" twist. The pressure peak resultant from the bullet being wedged into rifling that is say at 36 degrees (over the first inch) as opposed to being virtually straight in front of the throat should provide significantly less peak pressure and a smoother transition for the bullet.

Anyway, it should be interesting and fun to see how it all pans out. It will be interesting if nothing else.....

 

[Oliveralan]

Very interesting stuff. A few questions, how expesive is this 17-4 PH steel compared to 416? If it is so clearly better, I'm surprises it hasn't been done before. Seeing as this isn't an extremely new alloy or such, just a different, harder kind of steel. If going this way, what about using AR500 armor plate steel to make barrels??

Welcome to the site! Sound like
someone who will fit right in here, trying to push the limits and experimenting!

 

[Trickymissfit]

Well thats the idea of using 17-4 Ph, it is significantly more corrosion resistant than 416. In addition to the superior corrosion resistance it is approx 50% stronger than 416 and doesn't have the cold temperature failure issues that 416 has. Krieger for example will not sell a stainless tube in less than a #5 contour for this reason. Lothar Walther barrels use a material that is similar / same and I have had a giood run with those previously but they are button rifles and cannot have gain twist rifling.......... Which brings me to the next point. It makes more sense to have the rifling start almost straight and then progressively sped up to the ultimate twist rate. So for example a 30 cal tube would start out at twist rate of 1-100" and progressively get faster till it ends up in a 1-10" twist. The pressure peak resultant from the bullet being wedged into rifling that is say at 36 degrees (over the first inch) as opposed to being virtually straight in front of the throat should provide significantly less peak pressure and a smoother transition for the bullet.

Anyway, it should be interesting and fun to see how it all pans out. It will be interesting if nothing else.....

finally somebody got it right about just how junky 416 stainless is! But you did leave out the fact that it's a "high retained martensite steel" as well. This one of the main reasons 416 is not recommeded for use in extreme cold weather. One thing to keep in mind about 17PH4 rearc melt steel is that it will rust! If it will harden (with one known exception), it also will rust. The exception is MAR-10. MAR-10 is stronger than 416, and comes shipped with a 28-32 rc (you may be able to order at a higher hardness). Machines slightly tougher than 416, but I'd say it's similar to 420 in machinability. The stuff is so rust resistant that you can put a block of it in deionized water for six weeks with no sign of rust (416 is usually about 3 or 4 days)

So far most folks shy away from 17PH4 due to it's machining qualities, and tooling is closely guarded. So good luck to you! P.S. the stuff is kinda hard on equipment, and a Jap lathe rarely comes back after a good wreck machining the stuff. Also did do any investigation into the newer 500 series? I never did any work with that one, but the paper work looks very interesting.
gary

 

[Mikecr]

Who would/could finish them?
Who rifled and lapped them?

I'm interested

 

[sirrocco]

Well all these things have been done before - Barrels made from 17-4Ph (walther) and gain twists, by a number of people but not the 2 together. The reason most barrel makes dont want to use 17-4 is because it can prove to be a rather large pain in the *** to machine.
I havent priced 416 lately but am guessing 17-4 will be twice the price, maybe a little more. In addition to the price difference of the raw material the machining, drilling, reaming, rifling time will no doubt be extended and cutter life reduced. So the end result will have to cost a bit more. This exercise is not about making something cheaper tho', (there's truckloads of people out there doing that) its about making something better in every way possible. The end will be stronger, last significantly longer, more corrosion resistant and hopefully be as accurate, foul the same, with less peak pressure, as standard 416 tubes. Its nothing new really- just combining a bunch of "previously done" into one package.
Not sure of the machinability, temerature stability, or corrosion resistance of armour plate, so dont know whether or not it would make good barrels. There are other methods of hardening the surface of barrels to achieve similar results that we will also be experimenting with. Perhaps barrel makers like the idea of built in obsolescence? So they can sell more.....

 

[Trickymissfit]

Very interesting stuff. A few questions, how expesive is this 17-4 PH steel compared to 416? If it is so clearly better, I'm surprises it hasn't been done before. Seeing as this isn't an extremely new alloy or such, just a different, harder kind of steel. If going this way, what about using AR500 armor plate steel to make barrels??

Welcome to the site! Sound like
someone who will fit right in here, trying to push the limits and experimenting!

if memory is right Lothar Walther was the first person doing 17-PH4. He designed all his own tooling as he couldn't find anything that would cut barrels (what is different is closely guarded). For machining the rest; Valenite is your friend. I had it gun drilled before (usually .500" or bigger holes), and it seems to drill very well. (we used Pratt Whitney gun drills with custom designed gun drills). Needs a lot of coolant pressure in the bushing box (I mean A LOT), and the coolants will either kill you or be your friend. Also the feed rate is picky, and you must really push the drill or it will work harden on you.

Armor plate is not all that hard, but is extremely tough. It will work harden when you cut it unless you really push the tool into the part. Tool pressure is way up there, and tends to make bearing manufacturers happy. This stuff also requires some heavy equipment (once again for the Jap stuff). I made a lot of money repairing equipment that cut armor plate thru the years.

The material that interests me is ceramics. There have been a few ceramic gun barrels made in the past (military did a study about 15 years ago on M14 snipers rifles [shot very well by the way]). This would be a barrel that will not rust, has an extremely low wear factor, and appears to have a low node signature as well as a light weight.
gary

 

[sirrocco]

Well with regard to the rusting issue I cannot say that is my experience with 17-4ph, I have left deer blood on it for months and it hasn't even discoloured the surface. It is also recommended for offshore helicopter platforms by one steel supplier, so it cant be known for its rusting capability.
I think the machining issue is more about knowledge of "how to" rather than it destroying all ones gear. A year or so ago I rang 5 smiths wanting to get a couple of Walthers chambered and no one would do it cause they were too hard. In the end I gave up on the idea iof using a smith and got my local machine shop (that makes my Farquharson single shot reproductions) to ream the holes and we made a beautiful job of the chambers. Mirror bright and tight, a fraction larger than the reamer itself, with absolutely no issues in machining whatsoever. So I can only presume that there are many many pretenders out there. As the old expression goes, you sometimes gotta kiss a fair few frogs before you find a prince.
They will be finished and lapped by a at this point "relatively unknown" German machinist and barrel maker. We will be able to fit and chamber them for those interested.

 

[hammertyme]

I have used 17-4 a lot for the main reason it comes close to 28Rock when it arrives in the shop. We made lugs out of it as it saved heat treating. Very tough stuff but saved a lot of time in the end. Weld onto a barrel and away we went.

I much prefer the ease these days of the below. Copper does not come off in barrels with this treatment. At least I haven't seen any yet after 6 months of shooting.

Description of Finishes
Ferratic Nitride: This is the most advanced firearms finish we offer. Nitride offers exceptional wear resistance, excellent corrosion resistance and a uniform black color. This finish treats both the inside and outside of all parts of the rifle made of ferrous metal. Nitride will offer the benefits of a chrome lined bore without the disadvantages. As this finish is not a plating, but a heat treatment process, it actually changes the surface of the steel and preserves the finish characteristics (lapped finish) of the bore and can not flake off. Nitride will result in a surface hardness of nearly 70 Rockwell C scale, meaning that you can run a file across it and it will not scratch. Nitride is self-lubricating, eliminating the need to add oil to your firearm. This finish can be top-coated (with some surface prep) with DuraCoat or Film Transfer, allowing a variety of colors

 

[Mikecr]

We will be able to fit and chamber them for those interested.

Who is 'WE'?
This becomes rather important because most gun machinists would not risk screwing the job up because of a nontraditional barrel steel. So most shooters will run out of options here.
I know LW(the most capable barrelmaker in existence) had it worked out, but they put near zero efforts into an actual 'high expectation' barrel market.

Why not just market finished/accurized Blackstar barrels?
Or is that what this is?
I got no problem with it, just concerning out loud..

 

[Trickymissfit]

Well with regard to the rusting issue I cannot say that is my experience with 17-4ph, I have left deer blood on it for months and it hasn't even discoloured the surface. It is also recommended for offshore helicopter platforms by one steel supplier, so it cant be known for its rusting capability.
I think the machining issue is more about knowledge of "how to" rather than it destroying all ones gear. A year or so ago I rang 5 smiths wanting to get a couple of Walthers chambered and no one would do it cause they were too hard. In the end I gave up on the idea iof using a smith and got my local machine shop (that makes my Farquharson single shot reproductions) to ream the holes and we made a beautiful job of the chambers. Mirror bright and tight, a fraction larger than the reamer itself, with absolutely no issues in machining whatsoever. So I can only presume that there are many many pretenders out there. As the old expression goes, you sometimes gotta kiss a fair few frogs before you find a prince.
They will be finished and lapped by a at this point "relatively unknown" German machinist and barrel maker. We will be able to fit and chamber them for those interested.

I don't think it's the hardness of the steel as much as it is in the method. If you can machine 330 or 349 stainless then you can do this. Was trying to remember what we used for coolant yesterday, but I just can't remember. I do know it was different on the lathes than it was on a machine center. With a grinder we just used the same stuff, but made a wheel change.

Find a quart of standard low grade de-ionized water and put a block of hardened stainless in it. You'll see rust start to form with in 14 days. If it's a high grade de-ionized water you'll see rust in less than a week. But if you take a piece of 300 series steel and do the same; it may never rust. De-ionized water is often used in labs to accellerate rust, and if the item will rust the water will bring it on.
gary

 

[specweldtom]

I did a search for mechanical properties of 17-4 PH stainless steel. The data is a little difficult to correlate. I was particularly looking for low temperature impact properties. The only charpy v-notch values I could find for the solution annealed condition were at room temperature. Different companies supply the material in different heat treat conditions. It appears to me that for our purposes, the H-1025 or H-1075 condition would be about an optimum balance of strength, toughness, and machineability. Mechanical properties in these two conditions would be approx 135,000 psi yield strength, 155,000 psi ultimate tensile strength, an acceptable low temperature toughness of 15 ft/lbs at -100 deg F, and a Rockwell hardness of C- 31 to C- 33.

The "A" condition (solution annealed with no subsequent heat treatment) would be a possible choice for barrel steel. Yield strength of 110,000 psi, ultimate tensile of 150,000 psi, but impact properties listed only at room temperature (30 ft/lbs). You could interpolate impact toughness at lower temperature, but that's unacceptable for gun work. Only tests at the lower temperatures would prove its actual toughness. I'm sure they've been done, but I couldn't find them.

I mentioned the difficulty of correlating mechanical properties. This steel is precipitation hardened, and the soak temperatures (not soak times), have a drastic effect on its mechanical properties. The H-900/925 heat treat gives ultimate tensiles approaching 200,000 psi, but simultaneously improves toughness somewhat. By contrast, the H-1150 treatment tempers the hardness back to about 28 Rc, lowering yield strength back to 110,000 psi, and ultimate tensile strength to about 145,000 psi, but greatly improves low temperature notch toughness (to approx 45 ft/lbs at -100 deg F).

Sirrocco mentioned corrosion resistance as an advantage. My take on the issue is probably significant improvement in erosion resistance over 416 R. Increased barrel life. It's the primary reason I bought a LW Blackstar barrel off this site quite awhile back and chambered it for .30 x .378 Wby. I found the barrel to be tough (crunchy) and had to do some experimenting to get a nice chamber finish. The tenon was not difficult with carbide tools. I haven't been able to shoot the rifle enough to reach any conclusions on accuracy, let alone barrel life. Bottom line, I still don't know how accurate it will be or how long it will last. My opinion however is that a 17-4 PH barrel can be as good as a 416 R barrel, and will last longer.

I've been wanting to research this steel for a long time. Gary had pretty well covered it except for the low temp toughness, but I tried to sum it up so that even I could understand it.

Tom

 

[Trickymissfit]

I did a search for mechanical properties of 17-4 PH stainless steel. The data is a little difficult to correlate. I was particularly looking for low temperature impact properties. The only charpy v-notch values I could find for the solution annealed condition were at room temperature. Different companies supply the material in different heat treat conditions. It appears to me that for our purposes, the H-1025 or H-1075 condition would be about an optimum balance of strength, toughness, and machineability. Mechanical properties in these two conditions would be approx 135,000 psi yield strength, 155,000 psi ultimate tensile strength, an acceptable low temperature toughness of 15 ft/lbs at -100 deg F, and a Rockwell hardness of C- 31 to C- 33.

The "A" condition (solution annealed with no subsequent heat treatment) would be a possible choice for barrel steel. Yield strength of 110,000 psi, ultimate tensile of 150,000 psi, but impact properties listed only at room temperature (30 ft/lbs). You could interpolate impact toughness at lower temperature, but that's unacceptable for gun work. Only tests at the lower temperatures would prove its actual toughness. I'm sure they've been done, but I couldn't find them.

I mentioned the difficulty of correlating mechanical properties. This steel is precipitation hardened, and the soak temperatures (not soak times), have a drastic effect on its mechanical properties. The H-900/925 heat treat gives ultimate tensiles approaching 200,000 psi, but simultaneously improves toughness somewhat. By contrast, the H-1150 treatment tempers the hardness back to about 28 Rc, lowering yield strength back to 110,000 psi, and ultimate tensile strength to about 145,000 psi, but greatly improves low temperature notch toughness (to approx 45 ft/lbs at -100 deg F).

Sirrocco mentioned corrosion resistance as an advantage. My take on the issue is probably significant improvement in erosion resistance over 416 R. Increased barrel life. It's the primary reason I bought a LW Blackstar barrel off this site quite awhile back and chambered it for .30 x .378 Wby. I found the barrel to be tough (crunchy) and had to do some experimenting to get a nice chamber finish. The tenon was not difficult with carbide tools. I haven't been able to shoot the rifle enough to reach any conclusions on accuracy, let alone barrel life. Bottom line, I still don't know how accurate it will be or how long it will last. My opinion however is that a 17-4 PH barrel can be as good as a 416 R barrel, and will last longer.

I've been wanting to research this steel for a long time. Gary had pretty well covered it except for the low temp toughness, but I tried to sum it up so that even I could understand it.

Tom

I'm with you Tom! 15-5 and all the way into 18 & 19 series are steels I'm not at my best. I had some 15-5 laying around for a project, but never had the time to cut a chip. 17PH4 is one that I've done some things with, and it's an extremely strong steel, but I never was completely in love with it for an ordenance grade steel (somebody probably knows more than I do). What I found out was that 17PH4 rearc melt and MAR-10 were very similar, but with the latter being much more rust resistent. I could not see any advantage one had over the other in high heat, but others thought the MAR-10 seemed to come out with a better surviving thread form under serious heat (as I said I could see no real difference). But what I did see was a steel that fit somewhere between 330 and 349 stainless, but seemed to have a little carbon to harden. Both steel were shipped 28-32rc, but when you were cutting it you knew the difference. The shavings comming off MAR-10 were extremely hot! Was one stronger than the other? This I'd have to research again as I don't have the paperwork in front of me. (I'd guess they were similar in shear and tensil strength). But MAR-10 is expensive! I remember buying three six foot rounds five inches in diameter at $6500 about seven years back. The stuff was so tough that when we tried to cut it in a Makino MC the drives went into fault! Ended up cutting it on a big G&L MC that just groaned all the time it was working. I'd be afraid to run it on an Okuma lathe unless it was a big one. Tool pressure is serious. Kinda reminded me of a long day with Graphmo
gary