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Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
Cold Barrel Shots
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<blockquote data-quote="Teri Anne" data-source="post: 2294786" data-attributes="member: 118816"><p>In the one shot every hour for 12 hours one has to take into effect that it's not only the lighting that will change. Wind will vary, temperatures will vary, barometric pressure will vary, temp of the so called cold bore will vary as will the temperature of the individual cartridges being fired. Yes, the brightness or darkness of the day with light changing accordingly will affect the point of impact unless the shooter makes allowances for that change, which an experienced shooter will do for all of the variables. Based on my experience the two variables that will make the most difference is heat and wind. Heat can change the muzzle velocity out of a cold barrel. Depending upon what you read changes in temperature can change the muzzle velocity between 1.5 fps to 1.7 fps per degree of temperature change. At one point the Army said that for each 10 degrees of temperature change the muzzle velocity would vary up to 100 fps, which is probably a bit extreme for today's modern ammunition. One thing that I have actually observed is hunters zeroing their rifles prior to the hunting season. It's a nice warm fall day on the range, temperature comfortably in the mid to high 70's. As an example where I am today in Wisconsin the high temp is forecast to be 79 degrees. If I zero my rifle today, then take it out into the woods in November for the deer season the temperatures will be, let's say for example 20 degrees means a difference of 59 degrees. a 59 degree difference will mean (using 1.5 fps for each degree of temp change) around an 88.5 fps decrease in muzzle velocity. Add that to the now cold soaked rifle and barrel (remember things shrink as they get colder) where the action is not as securely held in the action due to shrinkage and the scope mounts not gripping quite as well as they did at 79 degrees and that is why a lot of hunters end up shooting below the target and incredulously watch the deer of a lifetime bound away unscathed. The variables change with each and every shot, and no two shots are ever quite the same, even when shooting 10 rounds in a 60 second time limit during competition. The big variable here is the temperature of the barrel/action which increases with each shot and that is why it's important to have a rifle that barrel temperature does not adversely affect it's zero.</p></blockquote><p></p>
[QUOTE="Teri Anne, post: 2294786, member: 118816"] In the one shot every hour for 12 hours one has to take into effect that it's not only the lighting that will change. Wind will vary, temperatures will vary, barometric pressure will vary, temp of the so called cold bore will vary as will the temperature of the individual cartridges being fired. Yes, the brightness or darkness of the day with light changing accordingly will affect the point of impact unless the shooter makes allowances for that change, which an experienced shooter will do for all of the variables. Based on my experience the two variables that will make the most difference is heat and wind. Heat can change the muzzle velocity out of a cold barrel. Depending upon what you read changes in temperature can change the muzzle velocity between 1.5 fps to 1.7 fps per degree of temperature change. At one point the Army said that for each 10 degrees of temperature change the muzzle velocity would vary up to 100 fps, which is probably a bit extreme for today's modern ammunition. One thing that I have actually observed is hunters zeroing their rifles prior to the hunting season. It's a nice warm fall day on the range, temperature comfortably in the mid to high 70's. As an example where I am today in Wisconsin the high temp is forecast to be 79 degrees. If I zero my rifle today, then take it out into the woods in November for the deer season the temperatures will be, let's say for example 20 degrees means a difference of 59 degrees. a 59 degree difference will mean (using 1.5 fps for each degree of temp change) around an 88.5 fps decrease in muzzle velocity. Add that to the now cold soaked rifle and barrel (remember things shrink as they get colder) where the action is not as securely held in the action due to shrinkage and the scope mounts not gripping quite as well as they did at 79 degrees and that is why a lot of hunters end up shooting below the target and incredulously watch the deer of a lifetime bound away unscathed. The variables change with each and every shot, and no two shots are ever quite the same, even when shooting 10 rounds in a 60 second time limit during competition. The big variable here is the temperature of the barrel/action which increases with each shot and that is why it's important to have a rifle that barrel temperature does not adversely affect it's zero. [/QUOTE]
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