Accuracy is in the Deep Freeze

Accuracy is the ultimate test for a high-quality rifle evaluation. Deep cryogenic processing significantly increases rifle accuracy by relieving residual metal stresses in the barrel.

Does Deep Cryogenic Processing Really Help Accuracy?
Mr. Geza Nagy did an independent and unsolicited trial of the deep cryogenic process for a barrel and published the following results. He was firing a Kelbly built 6 PPC LV Rifle. Prior to treatment, 500 rounds were fired, with many of the target groups measuring between .350 and .500. The barrel was sent to Cryo-Accurizing (a division of 300 Below Inc.) of Decatur, Illinois for the deep cryogenic stress relief process and returned for trial. Five shot groups were tired into six tar-gets. After deep cryogenic processing the average was a very respectable .2245 grouping. His findings? "One thing was clear from the start.... there had been a tremendous increase in the accuracy of the barrel brought about by the deep freeze alone." (Excerpt from the December, 1994 issue of Precision Shooting.)

Residual stresses exist in rifle barrels from the original steel forming or forging operations and additionally as a result of the many different machining operations to finish the barrel. They create a complex invisible random pattern in the steel. A steel barrel expands from the heat generated by firing a round and stress impedes expansion. The steel barrel will then warp randomly off axis as it is heated from sequential firings. Residual stress will therefore cause a barrel to progressively "warp an arc" as it heats more from each round tired. A barrel placed in a vise and fired repeatedly will show a resulting arc of round placement at the target. No two barrels are the same. The effect has a memory and will continue group after group of shots tired.

This "loose cannon effect" is measured in microns at the barrel end. but the multiple of distance to the target amplifies the problem causing wide groups or patterns. The problem is not a crooked barrel, but one which moves on repeated firing. Residual stresses are uneven and located variously throughout the structure. Deep cryogenic processing of metals is acknowledged as an exceptionally effective method for decreasing residual stress. Deep cryogenic processing also increases the durability, or "wear life" of steels.

How Does Deep Cryogenic Process Relieve Stress?
Stresses in steels are created by mechanical methods such as machining, boring and forming. Residual stresses are also created in castings or forging as a result of differential cooling. "Thermal stresses are created in steels after heat treating through the quench hardening process. An ice cube when dropped into a cup of hot coffee illustrates this effect. The heating creates expansive stress on the exterior of the ice cube while the core is still frozen. The result is stress shear or cracking due to the differing rates of thermal "growth" caused by the coefficient of expansion.

Dropping a rifle barrel into liquid nitrogen would have the same effect, creating stress. Stress relief (the opposite effect) takes place when the entire mass is at an equal temperature (core and surface) and cycled through a wide temperature range. Taking a mass to extremely low temperatures also creates a very dense molecular state. Technically, absolute zero (-457°F) is the zero motion molecular state of mass. If the rate of temperature change is slow enough, thermal compression and expansion take place equally from the core to

the surface, releasing internal stresses. The result is a homogeneously stabilized material. Understandably, this process takes a long period of time (more than a day) to keep the entire mass in equilibrium through the temperature cycling.

The deep cryogenic process also creates increases in the wear life of tool steels, sometimes increasing life by over 300%. Tensile strength, an increase in toughness, as well as greater stability through the release of internal hoop, compressive and tensile stresses are all benefits of cryogenic processing. Deep cryogenics (below -300°F) has created many new applications in science. High temperature superconductors, the super-conducting super-collider, cryo-biology, magneto-hydrodynamic drive systems for ships, and low temperature physics have all developed recently through cryogenic research.

Process Developments
The deep cryogenic tempering process for metals is now inexpensive and very cost effective (less than $50 per barrel) due to recent developments. Of all the dollars spent to perfect accuracy, deep cryogenic processing may prove to be the greatest benefit for the lowest cost. The process is a one time permanent treatment, affecting the entire part, not just the surface. New and used rifles both benefit from the treatment. Many additional steel parts receiving wear such as: drill bits, end mills, surgical scissors, bearings, racing engines, slicers and granulator knives also benefit from the inexpensive treatment. New applications are being discovered regularly. Even saxophones and trumpets benefit with easier play and truer notes. Some music professionals are hailing the process as the greatest advancement for musical instruments in the last fifty years.

The computer of a cryogenic processing system can be programmed to duplicate the optimal cooling curve, exactly within 1/10 of one degree Fahrenheit, so the mass descends at an even, slow rate. The computer control is repeatable, time after time after time. A contractor for NASA in 1994 hailed the new high technology Cryogenic Processing System as the most accurate thermal system they had ever evaluated. The system used for barrels was also used to stress relieve an optical bench for NASA's new planetary probe. Deep cryogenic processing is a stress relief specification for NASA.

The new deep cryogenic tempering equipment is coming out of the laboratory and into the marketplace. Over 50 deep cryogenic processors are now used worldwide.

The Deep Cryogenic Tempering Processor
The new machines process rifle barrels with controlled dry thermal treatment. "Controlled" simply means that the process is performed according to a precise prescribed time table. A 486 computer acts as a process controller to operate the descent, soak and ascent modes. The material is cooled slowly to -310°F, held for a day then raised to +310°F, and slowly returned to room temperature. The "Dry" process prevents the rifle metals from being subjected to liquid nitrogen, and eliminates the risk of thermal shock. The inexpensive manufactured pre-programmed system is now as simple as placing an item in the freezer and pushing a button.

Economy
Since liquid nitrogen is the largest processing cost. a cascade compressor system using electricity cools the chamber to -110°F, where it seamlessly transitions to LN2 to continue the descent to -130 F. Thermal transfer is what the processor is designed to do, and the more efficient the better. Transfer of cold from the LN2 to the metal rifle parts being treated-without losing the therms to the outside-is the difficulty, because holding anything that cold, for that long, is a challenge. Efficiency from super insulation and electricity cuts the processing cost in half, making it economical for all kinds of items, not just rifles.

Completing the Heat Treating Process: Martensitic Transformation for Tough Barrels
Metals are affected by heat treating. "Heat treating" is really a misnomer. It really should be called "cold" treating. The beneficial changes that heat treating imparts to metal don't actually take place from heating, but rather from the cooling or "quenching" from a high temperature. The changes don't stop at room temperature, but continue all the way to absolute zero. Deep cryogenic processing can he thought of as an extension to heat treating. A research metallurgist at the National Bureau of Standards, speaking of cryogenic processing stated, "When carbon precipitates form, the internal stress in the Martensite is reduced, which minimizes the susceptibility to micro cracking. The wide distribution of very hard, fine carbides from deep cryogenic treatment also increases wear resistance."

The study concludes: "...fine carbides and resultant tight lattice structures are precipitated from cryogenic treatment. These particles are responsible for the exceptional wear characteristics imparted to materials by the process, due to a denser structure and resulting larger surface area of contact, reducing friction, heat and wear." The process is not a coating, but a permanent, irreversible change completely through the metal structure.

New Findings for Longer Wearing Barrels
The subjected metals also develop a more uniform, refined micro structure with greater density. These particles were known, but never quantified scientifically until recently. "Carbide fillers" are precipitated as a result of the deep cryogenic processing. In a university study from Jassy Romania, the carbides were shown to have tripled in the structure after cryogenic processing. The carbides fill the open spaces, or micro-voids, resulting in a much denser, coherent structure of the steel. The end result is increased wear resistance (think of glass rubbing against glass, as compared to sandpaper against sandpaper). These particles were identified and counted using a scanning electron microscope with field particle quantification (an automatic particle counter). It is now believed that these particles are largely responsible for the great gains in wear resistivity. The change created is uniform throughout the steel unlike coatings, and will last the life of the steel, regardless of any subsequent finishing operations or regrinds. It is a permanent irreversible molecular change.

Set Your Sights, Hit Your Target
Wind, temperature, vibration and personal skill are enough variables to keep you busy. A moving barrel should not be part of the equation. Among the properties which define the attributes of a high quality rifle, accuracy is the highest importance. Cryogenic processing increases accuracy of rifle barrels. The process is now available to the rifle market under the trade name "Cryo-Accurizing".