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Post by fletch on Feb 22, 2009 8:49:13 GMT -5
I wanted to see how much a bullet would shrink when chilled. (Just got a dig. caliper) I put 5 different bullets in the freezer for about 1/2 hour to see how much they would shrink. This would or could approximate hunting in sub freezing temp. and although the gun barrel would constrict also the bullets being different metals could change the tightness.
What I found is very thought provoking to me.
The 5 bullets from .40 up to .50 seemed to shrink .002, but did not return to their original dimensions. They all only went back up .001. I tried re chilling them and thawing several times and got the same results. The bullets were 200 gr. SST .40, 250 gr.SST .452, Barnes 300 gr. solid copper .451, Barnes 290 gr. .500( a 54 cal. with sabot) and the new Hornaday FPB .500.
It would seem that if you have a tight fitting bullet and want to reduce the diameter you could chill and it would load a little easier especially if loaded into a warm gun barrel.
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Post by rexxer on Feb 22, 2009 8:57:37 GMT -5
Interesting Fletch
Are you sure the barrel reduces in diameter when it gets cold. I'm visualizing looking down the barrel as a donut. When it gets cold the metal would contract. It would seem that the outside dia would get smaller but the inside would get bigger. Might not be true but worth a thought. ;D
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Post by Dave W on Feb 22, 2009 9:43:35 GMT -5
Your test seems to correspond with my experiences with the 300SST sabotless. When I shot it above freezing it was hammer tight, meaning you almost need a hammer to get it started, below freezing it still fits tight but is nowhere near as hard to get started in the barrel.
Throw a couple of those Parkers in the freezer boys. ;D
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Post by jims on Feb 22, 2009 10:15:17 GMT -5
I have chilled a number of bullets to get them to fit in my .375 barrel sabotless. I never let them warm back up and rechecked their size. I will do that. I always expected after enough time that they would return to their original full size. If indeed that does work then there is less need of using the resizer.
I have to admit I think given enough time that they must return to the factory size but I will test it out.
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Post by ET on Feb 22, 2009 10:16:26 GMT -5
Rexxer
When a hollow cylindrical metal object is heated both the ID & OD expand outwards and vice versa when it is chilled. This little I do know.
Fletch
That is an interesting experiment. I know when certain metals are heated to a certain point and are allowed to cool they will shrink to a certain point. This is why when you heat say the one side of a steel plate and allow it to cool the plate curls inwards on the heated side. This is often used in industry when trying to form or contour certain metals in a specific direction.
Never heard of this happening when using cold temperatures and the temp range difference for heating has a far greater extreme range. But have to give this a try and see if duplicate results are obtained as I find this interesting.
Ed
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Post by fletch on Feb 22, 2009 11:58:58 GMT -5
No I am not sure that the inside of the barrel constricts when chilled and have not way to measure if it does. What I did find while looking for info on line was that there is a very expensive memory alloys of copper and other metals is used sometimes because it has a memory when reheated to a certain temp. and will return to its previous shape. the copper might return to its previous diameter if heated but I did not want to melt the plastic tips trying this.
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Post by skin290 on Feb 23, 2009 9:04:35 GMT -5
Seeing that you are only ranging between .002 and .001 differences and there is some inconsistency (knowing that the bullets HAVE to come back to size, per materials laws), I think that you probably need a better measurement device than a digital calipers. Even the best models of those can be .001 off at times, when I was using one a LOT for mold and die making, I could "maybe" feel good about .0005, but not as an exact measurement, just "if it shows .4995, I am reasonably certain that it IS somewhere below .5000, but not exactly how far"
And this is with a pair of calipers I had A LOT of time with, not ones I just picked up, so I knew their "feel" very well.
You should find a micrometer to take the kind of measurements you want, IMO.
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