Ambient temperature and case sizing

[swampratt]

Some of you know I am doing a: When will the .308 case fail.

I was measuring my cases shoulder set back after sizing and in the early morning I get .001" set back as the day went on I was pulling the shoulders forward .003".

So as the day got hotter the temp change changed my case size.

I pulled the press indoors and sized some cases and most were having the shoulders pulled out .003"
Then a few hours later i sized a couple more and measured and with that same setting I am now pushing the shoulder back .007".

I then reset the FLS die and got it to set shoulders back .001" this is inside the house temps in the upper 70's.

I then took the press outside and with dies in it, let it soak in the sun for 45 minutes.
Took it back inside the house and immediately sized a couple more cases.. you guessed it I am no longer getting .001" set back .. I am pulling the shoulders .003" forward.

Who knows what I was doing ton the brass cases as the day went on during that fail test.

Probably setting them back .001" or maybe .007" then pulling them forward later in the day.

I post this for all of you that reload in the environments that the temps are not the same and you think setting the die the same results in the same sized case.

If you wonder why your loads you loaded rounds act different with same load but some made in the winter garage and some in the hot summer garage.. this could be the cause.. something to think about.

 

[swampratt]

I warmed a rock Chucker press in the oven to 112 F with the die in it.
It did the same thing as my Lee 4 Hole turret press It pulled the shoulder .003" forward

 

[OKCHunter]

Interesting. Thanks.

 

[gfercaks33]

That's really cool info, thank you for spending the time to do that.

 

[okietom]

I have worked grinding carbide rotary slitting knives. Our final finish grind used a custom made 2-4 micron diamond wheel. When we were starting to learn how we found that we had to condition the part for thirty minutes in the cooling water in our grinder.

It took that long for the part to shrink enough that our infeeds would grind.

If we touched off and started infeeding the part would shrink more than the total infeed amount of the grinding cycle.

When you are concerned with close tolerances temperature is very important.