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Cold Bore Shot usually higher?

 
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  #1  
Old 11-15-2013, 03:08 PM
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Cold Bore Shot usually higher?

Since metal expands with heat and shrinks with cold.. Is the cold bore shot usually higher? My thinking is that the barrel was tighter with first shot making a slight difference in pressure and velocity. Then the last two shots were about the same temperature... Or maybe I just pulled the first shot...

I shot 3 shots at 325 yards with my 308 today. The first shot was about 3 inch high and the last two shots were not... Wish I would have shot one more round just to find out. Thoughts? If cold bore shot is going to be higher, this might need to be taken into account when hunting long range.

Btw, the barrel was dirty and not clean. It had 20 rounds through it before I shot the 3 rounds today.



DoubleG
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Old 11-15-2013, 05:30 PM
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Re: Cold Bore Shot usually higher?

True about expansion but a barrel has a hollow core and therefore the metal expands into the barrel hollow core and tightens as it is heated.

I think you need to shoot more groups over time to determine if cold bore hits are consistently high. I have found on a fouled barrel with low es reloads my first round impacts are consistent with strings of fire. For example a few weeks ago I shot at 1220 cold bore. Shot a follow up to confirm and it hit almost exact same spot. 3rd shot with windage and elevation adjustment.

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Old 11-15-2013, 05:43 PM
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Re: Cold Bore Shot usually higher?

My point is simply to show that the 1st 2 rounds were grouped together and both on cold bore. I intentionally shot the same POI. In this case the wind was about 3 mph and coming up the back side of the mountain which created a high and right impact. 3rd shot was 1 MOA down and 2 MOA left change to get me close to the target rock. I shot a little left as you see. However, that is very small rock so I was not to unhappy about the shooter and rifle performance.

Last Friday I had a friend and writer photographer out shooting. At 1486 yards the first round elevation and follow up shots had very little change.
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Old 11-15-2013, 06:35 PM
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Re: Cold Bore Shot usually higher?

Unless there's a problem with the floating, bedding, or torquing of the action bolts the odds are it's a shooter error. Most likely you added a bit of additional lean into the rifle just as it was going off.

This is a pretty common error when you "push the shot" meaning you inadvertently give a little extra forward push at the critical moment.
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Old 11-16-2013, 12:38 AM
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Re: Cold Bore Shot usually higher?

I notice on a chrono if a person holds the rifle super tight fps can be higher than following shots as the shooter settles down. Just a thought. Not sure how often that happens tho.
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Old 11-16-2013, 01:13 AM
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Re: Cold Bore Shot usually higher?

Quote:
Originally Posted by BrentM View Post
True about expansion but a barrel has a hollow core and therefore the metal expands into the barrel hollow core and tightens as it is heated.
While this seems true it is incorrect. A hollow tube when heated will expand away from its central axis. When I first started in manufacturing I argued with a machinist of 30 years that heating a tube would shrink the ID. He simply laughed at me and told me to heat it and then measure it and I would see the ID was bigger. He was right it had grown.

We used this principle to press fit sleeves onto the ends of shafts for giant mixers. The sleeves were impossible to slip over the ends of the shafts at room temperature, but a little heat would expand the ID and they would slip right on. Once cooled they would be so tight you would almost think they were welded.
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  #7  
Old 11-16-2013, 09:18 AM
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Re: Cold Bore Shot usually higher?

I probably just pushed that first shot. I usually hold it tighter on first round then settle in... I will shoot some more to confirm... It did get me thinking though
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