I have this 7x57 barrel that I am wanting to get rechambered, and back 10 years or so ago I had it cryogenically treated when that was the fad. When I talked to a smith here lately about having it cut back and rechambered he expressed some concern about the barrel damaging his reamer. It kind of threw me for a loop, hadn't thought about that. The way I understand it though, the deep freezing changes the structure of the steel and stress relieves it, but doesn't really harden it. It if made the barrel hard would you not then risk the danger of explosion and the barrel shattering in use? Just curious if any of you guys had dealt with the issue before.

Check your chamber for chatter.. perfected grains in steel cut BETTER

I've never cut in any manner a cryogenically treated steel of any kind.....but wouldn't hesitate doing it.....it should not make the barrel hard to cut and should have no effect on cutting tools....

Shilen gave me a couple barrels to chamber and asked if I could tell a difference. I picked the cryo barrel as the easiest to chamber. It is a form of stress relieving that is used in addition to the normal stress relieving in the oven. It does not replace the heat method, it is in addition.
Butch

Well, that was my way of thinking, was that the cryo treated steel was supposed to machine better... That was why it caught me off guard when he said something about it. I should clarify though, he didn't say it WOULD be harder, but that he had never done one and was concerned it MIGHT be. I should have been more clear in my original post I suppose. My fault.

quote:

Originally posted by butchlambert:
Shilen gave me a couple barrels to chamber and asked if I could tell a difference. I picked the cryo barrel as the easiest to chamber. It is a form of stress relieving that is used in addition to the normal stress relieving in the oven. It does not replace the heat method, it is in addition.
Butch

I found the same thing in machining two pieces of 4140. The cryo treated stuff was much easier on the tools. Almost like it wasn't hardened But a quick trip the the rockwell tester proved me wrong. The part was exactly as asked for 40 rockwell on the button.

I suspect that he was not concerned about the cyrogenics but about the fact that the erosion, stress cracking and hardening of the throat from firing will damage the reamer. The pilot of the reamer needs a good consistent bore diameter - rides on top of the lands - or the chatter will make it difficult to cut a good chamber or damage the cutting flutes.

quote:

Originally posted by KimW9:
I suspect that he was not concerned about the cyrogenics but about the fact that the erosion, stress cracking and hardening of the throat from firing will damage the reamer. The pilot of the reamer needs a good consistent bore diameter - rides on top of the lands - or the chatter will make it difficult to cut a good chamber or damage the cutting flutes.

How did you arrive at that?

The erosion of the throat changes the bore diameter - the pilot end of the reamer does not have a consistent (round) diameter to support the rest of the reamer. In addition, the eroded portion offers both an inconsistent surface to cut, and a surface of differing hardness from the nitriding of the throat area. These conditions do cause both chatter of the reamer and possible damage to the cutting flutes.

No, how did you come to your conclusion about what his gunsmith was thinking when there was no mention at all about a concern over throat damage leading to possible reamer damage in his post? I read the post six times and I never drew that conclusion. But then maybe I'm missing something.

Krieger has been rumored for a very long time to cryo barrels before some machining processes to make them easier to cut.

I'm no mind reader, so I can't discern your smith's reasoning other'n he may not be familiar with cryo'd steels and shied away.

Mark

(1) Westpac please note the first two words,

" I suspect that he was not concerned about the cyrogenics but about the fact that the erosion, stress cracking and hardening of the throat from firing will damage the reamer.

- I suspect - is my addition, not the inquirers.

(2) What does Cyrogenic Treatment actually do?. Cyro treatment is supposed to aid in completion of the Austenite/Martensite transition of the steel during heat treatment. The transition takes place during the tempering (or annealing) of the barrel for stress relief and involves physical movement of the atomic structure of the Iron atoms into different crystal forms - Austenite or Martensite. I enclose a link to

http://en.wikipedia.org/wiki/MartensiteWikipedia - which explains some aspects.

Subjecting the steel to temperatures of minus 196 degrees C (the temp of boiling Liquid Nitrogen - the most common coolant used) is supposed, repeat, supposed to make the crystalline structure of the steel more uniform, more free of stress and easier to cut or machine. It does not make the steel any different from a good steel batch and cannot cause damage to a reamer.

I presumed that this was known to the gunsmith.

It was the part about the cryogenically treated barrel that concerned him, not throat erosion. He had just never worked with a cryo'ed barrel before and had some concerns. The barrel is a 7x57 and only has about 500 rounds down it, and he would be cutting about .750 off the chamber end before he rechambered, so erosion should not be an issue. The original chamber job was not good, and that is the problem that needs to be fixed. I appreciate all the input from you guys, you have verified what I already believed to be true.

Kreiger is not rumored to use cyro, they do use it in addition to the furnace.
Butch

quote:

Originally posted by butchlambert:
Kreiger is not rumored to use cyro, they do use it in addition to the furnace.
Butch

On top of that he offers a Double cryo to those that want it.

Back when all of this cryo stuff started to come to the forfront, "Minus 300" actually advertised a hardening effect on the steel. Don't know if it was true or not but the bit about the austenite to martensit transformation is what most of the mold makers rely on when finishing some molds. It transforms the last 8% to 10% of the stress relief process that the heat cannot.

KimW9, I have somewhat of a grasp on heat treating and cryogenic processing of gun barrels. I have rechambered many barrels that have undergone the cryo treatments and have never encountered any problems brought about by throat erosion and my reamers. I "suspect" I was just curious as to how you came to suspect what you suspected when replying to the original post. That's all. No big deal, but thanks!

quote:

Originally posted by redial:
Krieger has been rumored for a very long time to cryo barrels before some machining processes to make them easier to cut.

Mark

That is not a rumor, it is a fact. Eleven years ago this year, I had a several hour conversation with John Krieger on that very subject. He told me he cryos all his barrel steel before drilling or rifling it. Says it cut his wastage by approximately 87%....apparently the cryo treatment makes it MUCH easier to drill a straight hole to his standards.

Now, it is possible he meant something different than what he said. His exact words were to the effect that it cut his wastage to 1/8th what it was before he started "cryoing" them all. But, he may have meant that it cut his wastage BY 1/8th, rather than TO 1/8th. Either way, he cryos them all and finds it makes them machine BETTER.