I thought the whole point of cryo was to relieve stresses so as the barrel heats up, POI will stay consistent.
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I thought the whole point of cryo was to relieve stresses so as the barrel heats up, POI will stay consistent.
When I was a tool and die maker apprentice (actually mold maker apprentice) all the old timers would go in a frenzy about late November making up their tools, jigs and fixtures then throw them in the snow over the 2-3 month winter and retrieve in spring for grinding and finishing. When I asked why, they said the cold relieves the stresses etc... Chicago winters are no where near as cold as a cryogenicaly treated barrel.
A few months ago I was going some research into the subject. I spoke with a few cryo shops including 300 below (seems there are a couple in IL which I found odd, but oh well I digress), of coarse I have to take what a sales person says with a grain of salt but the consensus I came to is that "if it aint broke, don't fix it." meaning if I had a barrel that shot well I wouldn't bother cryo treating it. If I had a barrel that should shoot but doesn't I might consider a treatment.
Buying a cryo barrel is another thing. The barrel on my personal AR is cryo treated, but I bought it that way. It is a RRA (who I am pretty sure use wilson blanks). Probably unnecessary since I don't have it setup for a long range precision shooter, but a swap of the optics and the trigger and it could fit a SPR role. If I were buying a rifle for precision work I would likely opt for a stainless cryo barrel. If I were buying a rifle for cqb, not likely I would care and would opt for a chrome lined barrel instead.
The premise of cryo treatment is that it is supposed to take the stresses from the machining process out of the steel. I'm sure alot more people with alot more experience could chime in on the subject.
From the Lilja barrel website-
Q. What is your opinion of the deep cryogenic processing of barrels?
A. The cryogenic treating of barrels at a temperature of -300 degrees below zero has been a hot topic of discussion lately. Our short answer is that it will not harm your barrel but we are not completely convinced of all of the benefits claimed by some. The only benefits that we feel are likely to result from the treatment are possibly a longer barrel life and a slight increase in machinability.
Claims for increased accuracy through stress relief are not founded in our opinion. When barrels are button rifled no material is removed, it is just displaced. This causes stresses to be formed in the steel. If these stresses are not removed problems will result. These negative conditions include warping of the barrel during other machining operations, an increase in the bore diameter towards the muzzle end of the barrel during the contouring phase, and in the extreme, lengthwise splitting of the barrel. Also, if there are stresses remaining in the barrel they can be slowly released as a barrel warms up during firing. This causes the barrel to actually move during the course of shooting, causing inaccuracy.
In our testing we have found that the only effective means to completely remove the types of stresses introduced during rifling are with conventional heat treating using elevated temperatures. The -300 degree treatment alone will not remove these stresses. We have been told by a knowledgeable metallurgist that the deep cold treatment will, at best, remove up to 6% of the remaining stresses in the type of steel used for rifle barrels. The key words here are remaining stresses. In other words if the barrel was not stress relieved conventionally, then only 6% of the original stress will be removed. If the barrel has been treated conventionally with heat and then brought through the -300 degree cycle, up to 6% of any remaining stresses could be removed by the cold treatment. We do know through our testing that the cold treatment alone will not remove any significant amount of stress and that the problems outlined above concerning stress will remain in the barrel.
So, because of the very limited amount of stress that could be removed with the cold treatment (if the barrel has been properly stress relieved with heat as our barrels are) we do not believe that there can be much if any accuracy benefit to the -300 degree treatment of our barrels. It is for these reasons that we feel the cold process has very little potential for increasing the accuracy of our barrels. In our opinion, other than the removal of these stresses, there are no other mechanical factors involved that could benefit accuracy in a rifle barrel, resulting from a heat treating operation, either hot or cold.
For reasons not completely understood however there may be an increase in the wear resistance of the steel. This type of wear however does not contribute greatly to barrel erosion. We invite you to read our comments on this type of barrel wear in the question regarding the use of moly coated bullets.
Another possible side benefit to the freezing process is a slight increase in its machinability.
Post Script: Since I originally wrote this an excellent article by Kevin Thomas of Sierra Bullets was printed in the September, 1998 issue of Precision Shooting magazine. Mr. Thomas found, in a controlled test, that there was little benefit to deep freezing match grade barrels. He could see no difference in accuracy but probably a slight increase in useful life. I would encourage anyone interested in this subject to take a look at this article.
Cryo is worth the money for a bolt gun where you expect long-term consistency and precision and your throat isn't damaged in lots of high-temp shooting.
In an M16 you'll reach end-of-maximum precision potential somewhere around 3,000 and 5,000 rounds (using a stainless cut-rifled barrel and shooting 77s and 80s in the National Match Course), so it's not really worth the cost if you're going through barrels on a regular basis. A little longer using a short throat and 69 to 77-grain bullets.
For 39 years, I worked in the industrial process control systems business. That got me into a lot of heat treating shops. Some of those shops occasionally did a cryogenic step when producing aerospace parts. What that did to the parts was to harden it more than a standard quench would. After the cryo treatment, they would put the parts into a draw (tempering) furnace to reduce the hardness (and stresses) to the desirable level for the parts.
The reason for the cryo treatment is simple. Had it not been done, some parts would re-harden and get more brittle when exposed to very cold temperatures such as when flying at high altitudes or going into space. The cryo treatment prevents this.
Based on what I learned over the years (though I am not a heat treating engineer), I cannot see how a cryo treatment would do much for a barrel that is never exposed to significantly sub-zero temperatures.
It works.
Longer life, some accuracy and they clean up marginally better.
Martensite precipitation at -300 F is the key. Martensite is an iron carbide. Extremely tough stuff but without the brittleness from a quench.
Smaller grain structure and they actually change geometry from body centered cubic to body centered tetragonal.
Does not affect Meloniting on surfaces.
Used in aerospace and Motorsports for too many components to list but brake discs, springs, rods, crank and heads are common items.
For a barrel the larger the internal stresses after manufacturing the better results after cryogenics.
The higher the Carbon content the greater the results of improved:
Micro-hardness (not much at all)
Refined grain structure
Crack Resistance
Wear Resistance
Toughness
Fatigue Strength
Machinability
Probably electrical properties (again, small if anything)
I knew one of the original developers, Ed Busch, of Cryo-Tech in Hazel Park, MI and worked with him for a few years. He had lots of research data which I absorbed like a sponge. After he passed his daughter sold the company to 300 Below.
Google is your friend; search "cryogenics, low carbon steel" and any of the characteristics mentioned.
"One man with courage makes a majority."
I had 300 Below treat several barrels including a Lilja rimfire match barrel some years ago. Fast service, and that lilja won some big matches. Now I had the barrel frozen before it was machined so I cannot say for certain it helped. Another barrel I had frozen was a Ruger 77/22 barrel that was used(aftermarket barrel). I can't say it shot better, but freezing definitely made a slight change to the fit of the barrel. The older 77/22's fit the receiver like a 10-22 and the fit afterwards was a tad loose. Both the mentioned barrels are stainless.
DPMS used to offer cryo treatment on any gun you special ordered from the factory. I am pretty sure they stopped doing this after they were bought out.