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Posted: 7/5/2009 11:14:35 AM EDT
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Hello,
I have an AR10 308 win and every time I shoot with it, the cold bore shot and every shot after cooling down a while, is about 1 inch higher than the rest of the groupment. The groupment after the first / cool down shot is very tight. Is there a logical explanation for this ? Thanks & kind regards, |
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That's just physics. 3 schools of thought-1- cold bore factor, 2, clean bore factor, 3, cold shooter factor. Guess what? They all exist. Cold shooter= YOU. Train to overcome this. Clean bore= different stuff going on in gun vs a fouled bore. Cold bore= the AR15 system heats up VERY quickly. This affects thing like barrell harmonics and velocity. The inability to crack the bolt slightly open to vent it on the range (like u could do with a bolt action) results in a oven-like atmospere in the chamber area, "supercharging" the bullet when fired and causing all types of havoc vis a vis velocities, etc. These temps are aggravated even more by things like high ambient temps (summer) or the use of a suppressor. Here is how I teach sniper students (using the SR25, Mk12 SPR, or M110) to correct for this: 1. know your cold bore affects at given distances, also in regards to things like altitude, ambient air temps, and RECORD this data. 2. Zero the weapon (esp. in summer) in 5 shot strings. Take a break after 5, drink water, reload, etc, with mag out and bolt locked to rear (venting). This will prevent supercharging. Another trick used by snipers is to clean the bore range-side after training, and fire a couple of shots to foul it before casing it. Supposedly this takes "clean bore factor" out of the equation.Cops are famous for this, but I have found no evidence that this actually has a significant impact.
Hope I didnt torture you too much. |
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