Bolt Action Receiver Metallurgy

GreatLandKennoZ · May 10, 2017

hello all, i am a Koyukon savage living here on mine and my people's homeland of Alaska. i am going to introduce the first ever gun invented by a westerner like myself. i have the design pretty much ready to be machined into a real life single shot prototype that i will improve upon until i have a working repeater design.

i was reading around and ran into some posts saying 32 rockwell for 4140 isn't enough to handle a catastrophic failure where the chamber/barrel turn into bombs. it got me wondering, what is the sweetspot for metal to be just hard enough to handle a high pressure round or barrel blockage, but be tough enough to not crack or be brittle.

i was planning on using 4340 with some vanadium, but ive heard it is more prone to cracking than standard 4140, not sure if this is true because i never really read those metallurgy books i have all the way through, just those big idea boxes off to the side.

if 4340 is suitable for action requirements, do you think 39 rc after heat treatment is right on the money or if i should go high or lower

basically this post is here to discuss the most premium alloy steels and hardening methods for making guns.

manufacturing would go something like order 4340 unhardened 1.5" round stock, drill bolt hole, broach raceways roughly, then send out to heat treat, and machine to final spec after heat treating. hope this discussion is broad and gives me new ideas and some insight into making guns that are safe

RWO · May 10, 2017

Carbon steel factory actions are usually made from 4140 or similar alloy and hardened to 36-40 Rc range. Miltary Mauser actions were softer than that and seem to hold up pretty well. I don't know if 4340 is inherently any better than 4140 unless you want to weld on it. I suspect it costs more than 4140.

Stainless steel actions are usually 416 or 17-4PH. Both machine freely in the hardened state. I particularly like 17-4PH H1025. It runs about RC 38 and machines nicely.

RWO

paramedico987 · May 10, 2017

The weak spot isn't in the receiver, on existing bolt guns; it's the bolt itself that would fail, first.
Of course your design could be different, but I doubt it.
Pretty much anything in the RC30's should be fine for standard cartridges.

GreatLandKennoZ · May 10, 2017

RWO said:
Carbon steel factory actions are usually made from 4140 or similar alloy and hardened to 36-40 Rc range. Miltary Mauser actions were softer than that and seem to hold up pretty well. I don't know if 4340 is inherently any better than 4140 unless you want to weld on it. I suspect it costs more than 4140.

Stainless steel actions are usually 416 or 17-4PH. Both machine freely in the hardened state. I particularly like 17-4PH H1025. It runs about RC 38 and machines nicely.

RWO

upon reading the heat treating steel chapter in one of my books(which is really what i should have done a long time ago) it said that 4140 obtains better hardenability farther below the surface( harder core or harder center) than standard 1040. i read on a barrel web page that 4340 is more of a pain to heat treat so im guessing that's why 4140 is the standard. the reason i thought 4340 would be superior is because it has more alloying elements that makes the metal tougher and less brittle, but after reading my books a bit more i think 41V40 is a great metal especially since you can just buy it and it's not that expensive

i will continue on searching the web and reading my machining and engineering alloys books, as i am sure they have many answers to my questions. sorry if i am asking some noob questions, and i do have the books to research into these subjects but haven't completed them yet, but i just thought i would get a quick answer from someone here. thanks for your time though

GreatLandKennoZ · May 10, 2017

paramedico987 said:
The weak spot isn't in the receiver, on existing bolt guns; it's the bolt itself that would fail, first.
Of course your design could be different, but I doubt it.
Pretty much anything in the RC30's should be fine for standard cartridges.

good point, i am designing a 4 lug with lugs bigger than the bolt bore so i hope my bolt design is more evenly matched with the receiver in terms of strength and fail points. the question is, when your gun blows up do you want the bolt to break or the chamber to explode lol. i have some clearer goals now, 4140 or 41v40 steel for both bolt and action, action 39rc and bolt 43 rc.

since these are guns that are going to be sold i pretty much have to blow up a few guns during testing, and while i hate to destroy the engineering marvel invented in china almost a thousand years ago but never seen on my homeland even 200 years ago, i am also looking forward to learning what happens when a gun explodes and how/why

i will tell of my endeavors with these thundersticks, thanks to all

another thing, i was planning on starting out with .300 win mag but i think 6.5 cm would be better because of the smaller bolt thrust/bolt face and it being a lower power cartridge

MIBill · May 10, 2017

If it were me (I HAVE scratch built actions) I would buy pre-hardened 4140 and work with that. It is readily available and a LOT cheaper than annealed and paying to have it hardened. I also find that pre-hardened 4140 machines well and produces a better surface finish with less refinishing required.

However, the biggest reason to use pre-hardened steel is that you have ZERO control over how your steel will warp or deform in heat treatment. It may not warp at all. It may banana.

GreatLandKennoZ · May 10, 2017

MIBill said:
If it were me (I HAVE scratch built actions) I would buy pre-hardened 4140 and work with that. It is readily available and a LOT cheaper than annealed and paying to have it hardened. I also find that pre-hardened 4140 machines well and produces a better surface finish with less refinishing required.

However, the biggest reason to use pre-hardened steel is that you have ZERO control over how your steel will warp or deform in heat treatment. It may not warp at all. It may banana.

this is what i want to know more about. the only way i can think of a part warping is from stress caused by rolling(do machined cast parts heat treat better?) or uneven heating or uneven cooling. i would think heat treating the part when it is as symmetrical as possible would help too, i.e. before the mag cut, screw holes, ejection port are machined.

anyways i think you are right, the cheapest and possibly best way to start is from already heat treated stuff.

another thing about warping, if you were to harden the parts to say about 47 rc and then anneal the part to relieve the stress, of course this will cost more but you would end up with a more thoroughly hardened part, along the bolt bore and raceways but still not warped enough to not simply machine it straight. idk, and heat treatment is one of the reasons i started this thread so thanks for the discussion

MIBill · May 11, 2017

GreatLandKennoZ said:
this is what i want to know more about. the only way i can think of a part warping is from stress caused by rolling(do machined cast parts heat treat better?) or uneven heating or uneven cooling. i would think heat treating the part when it is as symmetrical as possible would help too, i.e. before the mag cut, screw holes, ejection port are machined.

To be sure the risk of warping would be minimized by preforming the heat treat on a symmetrical part. But not eliminated. I don't see the need to delve further into that for the purpose of this discussion.

GreatLandKennoZ said:
anyways i think you are right, the cheapest and possibly best way to start is from already heat treated stuff.

It's how it is "normally" done by every manufacturer that I am aware of.

GreatLandKennoZ said:
another thing about warping, if you were to harden the parts to say about 47 rc and then anneal the part to relieve the stress, of course this will cost more but you would end up with a more thoroughly hardened part, along the bolt bore and raceways but still not warped enough to not simply machine it straight.

I'm confused by your comment. Annealing is the process of REMOVING the heat treatment. 47rc would be too hard, but why harden then anneal? Buy pre-hard 4140 in the mid 30's and move on. Some claim that a few points difference in the hardness between the bolt lugs and the receiver is beneficial. I have been using two different sources that achieve this. However, I started doing it do to cost.

GreatLandKennoZ said:
idk, and heat treatment is one of the reasons i started this thread so thanks for the discussion

GreatLandKennoZ · May 11, 2017

MIBill said:
To be sure the risk of warping would be minimized by preforming the heat treat on a symmetrical part. But not eliminated. I don't see the need to delve further into that for the purpose of this discussion.

It's how it is "normally" done by every manufacturer that I am aware of.

I'm confused by your comment. Annealing is the process of REMOVING the heat treatment. 47rc would be too hard, but why harden then anneal? Buy pre-hard 4140 in the mid 30's and move on. Some claim that a few points difference in the hardness between the bolt lugs and the receiver is beneficial. I have been using two different sources that achieve this. However, I started doing it do to cost.

yes, take it from 47rc to 39 by annealing or heating at warm but not too high temps. as i am aware, this will reduce stress and make for a more stable grain structure.

for now i will just use already heat treated, have you used both cold rolled and hot rolled before? i am inclined to use hot rolled

looking it up tempering is what i meant

cyanidekid · May 11, 2017

glkz, just a friendly tip, if, as it seems, (forgive me if i'm wrong) you are not familiar with some of these basic terms, go back to those books and spend some time.

good stuff to know BEFORE you try to engineer stuff that goes boom, just sayin..good luck and be safe..

GreatLandKennoZ · May 11, 2017

cyanidekid said:
glkz, just a friendly tip, if, as it seems, (forgive me if i'm wrong) you are not familiar with some of these basic terms, go back to those books and spend some time.

good stuff to know BEFORE you try to engineer stuff that goes boom, just sayin..good luck and be safe..

i am trying as we speak. i have elements of metallurgy and engineering alloys by Campbell F and Metallurgy Fundamentals - Ferrous and Nonferrous - D.A.Brandt and J.C.Warner

if there are any books, especially steel specific books and even better gun specific books to recommend, then let me know of your favorites as i will surely get them

MIBill · May 11, 2017

cyanidekid said:
glkz, just a friendly tip, if, as it seems, (forgive me if i'm wrong) you are not familiar with some of these basic terms, go back to those books and spend some time.

good stuff to know BEFORE you try to engineer stuff that goes boom, just sayin..good luck and be safe..

I'm getting a similar vibe here. I'm not sure that someone who requires such basic advice from a forum should be making firearms for sale.

wesg · May 11, 2017

GreatLandKennoZ said:
yes, take it from 47rc to 39 by annealing or heating at warm but not too high temp

This is normal practice for most hardening procedures. Heat to a specific temp and quench, which gives you full hard for that material. Then temper, or 'draw back' to the desired hardness.

That's what the pre-hardened material is.

MIBill · May 11, 2017

GreatLandKennoZ said:
yes, take it from 47rc to 39 by annealing or heating at warm but not too high temps.

Now I am very concerned with you endeavor. The questions and comments lead me to believe that you don't grasp these concepts in even the most basic way.

GreatLandKennoZ said:
as i am aware, this will reduce stress and make for a more stable grain structure.

4140 would be hardened to about Rc60 then tempered to the desired spec. There are a combination of factors that determine the finale characteristics of the steel. Grain structure and composition both play a factor.

GreatLandKennoZ said:
for now i will just use already heat treated, have you used both cold rolled and hot rolled before? i am inclined to use hot rolled

No I have not. And this is another part of why I am having concern with your endeavor. What are the advantages of one Vs. the other? Disadvantages? I make choices based on my goals and understanding the strengths and weaknesses.

GreatLandKennoZ said:
looking it up tempering is what i meant

My biggest concern is that you don't have a good enough understanding of the subject to weed out misinformation. Although nothing posted here is dangerously incorrect, there has already been misinformation. I suspect that you have no clue which bit of advice is not completely correct. To encourage you to learn the subject matter first, ask questions next and mace chips later, I'm not going to point it out. Like I said, the information is not dangerous. Just not totally correct.

GreatLandKennoZ · May 11, 2017

wesg said:
This is normal practice for most hardening procedures. Heat to a specific temp and quench, which gives you full hard for that material. Then temper, or 'draw back' to the desired hardness.

That's what the pre-hardened material is.

good to know

GreatLandKennoZ · May 11, 2017

MIBill said:
Now I am very concerned with you endeavor. The questions and comments lead me to believe that you don't grasp these concepts in even the most basic way.

4140 would be hardened to about Rc60 then tempered to the desired spec. There are a combination of factors that determine the finale characteristics of the steel. Grain structure and composition both play a factor.

No I have not. And this is another part of why I am having concern with your endeavor. What are the advantages of one Vs. the other? Disadvantages? I make choices based on my goals and understanding the strengths and weaknesses.

My biggest concern is that you don't have a good enough understanding of the subject to weed out misinformation. Although nothing posted here is dangerously incorrect, there has already been misinformation. I suspect that you have no clue which bit of advice is not completely correct. To encourage you to learn the subject matter first, ask questions next and mace chips later, I'm not going to point it out. Like I said, the information is not dangerous. Just not totally correct.

the difference between hot rolled is it is cheaper and has less internal stress and cold rolled is stronger but has lots of stress from cold working

Dave G. · May 11, 2017

MIBill said:
Now I am very concerned with you endeavor. The questions and comments lead me to believe that you don't grasp these concepts in even the most basic way.

4140 would be hardened to about Rc60 then tempered to the desired spec. There are a combination of factors that determine the finale characteristics of the steel. Grain structure and composition both play a factor.

No I have not. And this is another part of why I am having concern with your endeavor. What are the advantages of one Vs. the other? Disadvantages? I make choices based on my goals and understanding the strengths and weaknesses.

My biggest concern is that you don't have a good enough understanding of the subject to weed out misinformation. Although nothing posted here is dangerously incorrect, there has already been misinformation. I suspect that you have no clue which bit of advice is not completely correct. To encourage you to learn the subject matter first, ask questions next and mace chips later, I'm not going to point it out. Like I said, the information is not dangerous. Just not totally correct.

I'm in agreement with the above. I suggest you find a Metallurgical Engineer who will mentor you. If you are going build guns for sale, then they had better be safe. What will one of your prototypes cost to build - hundreds of dollars? Consulting with good engineer with knowledge of the metallurgy of gun making will be money well spent if he/she saves you just one or two additional prototypes or months of screwing around with the wrong materials. Even a metallurgist with no gun making knowledge would be able to set you straight on the basic heat treating principles and alloy selection.

GreatLandKennoZ · May 11, 2017

MIBill said:
I'm getting a similar vibe here. I'm not sure that someone who requires such basic advice from a forum should be making firearms for sale.

it'l be a while before that happens, i am not thinking of selling anything until i at least have a working repeater and i am currently making a single shot

i'll try to even hire somebody who went to college to help me at that stage, thanks for your help though

GreatLandKennoZ · May 11, 2017

Dave G. said:
I'm in agreement with the above. I suggest you find a Metallurgical Engineer who will mentor you. If you are going build guns for sale, then they had better be safe. What will one of your prototypes cost to build - hundreds of dollars? Consulting with good engineer with knowledge of the metallurgy of gun making will be money well spent if he/she saves you just one or two additional prototypes or months of screwing around with the wrong materials. Even a metallurgist with no gun making knowledge would be able to set you straight on the basic heat treating principles and alloy selection.

that was the plan, yes my prototype is probably going to cost around a grand atm for receiver and extractor-less bolt. thank you all for your advice, these are just my first few steps and i am sure there are going to be many

Bolt Action Receiver Metallurgy

Plastic

Cast Iron

Aluminum

Plastic

Plastic

Hot Rolled

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Hot Rolled

Plastic

Titanium

Plastic

Hot Rolled

Titanium

Hot Rolled

Plastic

Plastic

Cast Iron

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