Couldn't find the whole article just a summary, in any case, its something that was researched in Switzerland in regards to Sig assault rifle barrels
Swiss SIG (Schweizerische Industriegesellschaft)is not = as Sig Sauer US whose claim to fame is that it makes absolute crap and semi-finished products that need to go through at least one or two product recalls before its actually a market ready product
Hans-Peter Sigg is a renowned gunsmith and toolmaker involved not only in small arms but the development of autocannons and projectiles for them,In any case guy actually made a series of thermally insulated chassis where barrels were sealed inside a carbon fiber sleeve all tough that was meant for the slow fire of ISST type shooting.
In any case, bore cooling fans are BS, their best utility is making the competition annoyed with the noise
Machine translation
On the wear mechanics of firearm barrels
Assault Rifle Experience
After an assault rifle has been constructed, development work follows. The test weapons are checked for the regulations laid down in the specifications. If, for example, the specified goal is not achieved in a sand or mud test, the results are analyzed and changes are made to the design. This process is repeated until the result meets the specifications. Today, most of these regulations correspond to the standards specified in the MIL-STD tests. The regulations or requirements for single-shot accuracy and barrel life vary from country to country. So are e.g. the precision requirements in Switzerland for the Stgw.90 . During continuous firing, as is carried out in the above tests, a certain number of magazines per rifle are also tested for their durability and function. The shot rhythm, the type of cooling and the precision (scatter) after a specified number of shots of a specific ammunition are prescribed. As an example: The contents of five magazines, each with 20 rounds (= 100 rounds) are fired in 70 to 80 seconds. That's about 1.5 to 2 shots per second. While the five magazines are being refilled, the assault rifle stands upright over the entire length of the barrel and with the breech open to cool down in a container filled with water. After that, the assault rifle is blown out with compressed air and the firing continues until 8000 rounds of ammunition have been fired. Once it has cooled down and been cleaned, the assault rifle is then tested for precision.
If the barrel material, manufacturing process, thermal treatment, ammunition and firing rhythm remain unchanged in repeated test series, the result is largely the same. The question then arises as to why when used in shooting exercises - in contrast to the endurance test - the barrel of the rifle no longer meets the precision requirements much earlier and with a significantly lower round count and are burned out in the bullet bearing area, even though it was never really "hot". The barrel should have to be able to withstand significantly more than 8000 rounds of ammunition if it were shot "gently" and hardly got warm! To solve this problem, various possible solutions have so far been advertised, e.g. with a chimney effect in the forearm area, with ventilation slits, with enlargement the barrel surface with longitudinal grooves or with radial cooling ribs for better cooling of the barrel. A lot of money was invested in order to get to the bottom of the processes of wear and tear (and for cost reasons not by gun factories that exclusively produce firearms).
The secret was revealed with a scanning electron microscope, which can display magnifications down to the nanometer range (1 nanometer = 1 billionth of a meter). smooth. With the first shot – usually an overpressure shot (European CIP tests)with >6000 bar pressure – gas at around 3500°C is pressed into the micro-surface of the throat barrel area. The steel in this surface area expands and compresses
The rapid cooling of the barrel then cracks the microsurface. However, there is also a hardness structure with changes in volume and tension builds up, which in turn contributes to the crack mechanics. A lattice crack pattern is created, very similar to the lattice pattern of a reticulated giraffe. The second shot now impacts a surface that is open due to these microcracks. The surface is therefore different for the second and subsequent shots than before the very first. The cracks close again when the surface is heated again during the second shot, but only through the expansion of the material after the heat has already penetrated. During the subsequent cooling, the cracks open again
The barrel material at the edges of the tear heats up more easily and quickly than in the small, closed areas and burns off more intensely. If the inner surface of the barrel cooled less and more slowly, the cracks would be narrower or remain almost closed. And here lies the solution to the riddle! Barrels will be shot out faster if only one shot is fired every few minutes. The cooler the barrel when the shot is fired, the more it damages it. The reverse conclusion would be that the service life of the barrel is longer, the warmer it is when the shot is fired. However, this only applies up to the temperature at which the strength of the barrel steel can be maintained. If, for example, an assault rifle or machine gun is continuously fired, this limit is quickly exceeded and wear and tear increases rapidly.
In the case of sporting repeating rifles, on the other hand, this temperature limit is not reached and therefore cannot be exceeded. On the contrary. In the case of rifles designed to fire slowly, the barrel should remain as warm as possible. Insulation that prevents rapid cooling would do prolong the life of the barrels
The crack pattern created on the very first shot remains the same throughout the life of the barrel. But the edges are becoming more and more rounded and the cracks are getting deeper and wider. These cracks and crack patterns are already clearly visible with a barrel endoscope after about 1000 shots (see picture). The consequence of this is that the barrel burns out where the gas pressure and temperature are highest and where the gas turbulence is greatest, or to put it another way: where the temperature difference between gas and barrel temperature is greatest!
Heat distribution in the barrel. Especially with rifles with wooden forends, after a few shots, heat builds up between the stock and the barrel. Thermal imaging cameras were able to uncover this deficiency
Aluminum stocks around the barrel are thermally better than wooden stocks, but the warming of the barrel can produce a chimney effect when shooting, which on the one hand unnecessarily cools the barrel and on the other hand can cause tension on the barrel circumference due to the ventilation (heat differences).
Not only does this damage the barrel when shooting in low outside temperatures, but it also becomes noticeably tense if the barrel is touched with a finger of the hand holding the fore-end, which happens every now and then. Changes in the point of impact could be observed immediately. On the other hand, when shooting at temperatures above 30°C, the barrel is no longer thermally affected when you touch it with your finger. ( think they meant slight contact sling shooters could make) ...........
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