Re: Outside Temp/Pressure
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Clark</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: TX-Stars</div><div class="ubbcode-body">
Clark, I am unaware of how to calculate safety margins on loads. Information on how to do so would be greatly appreciated.
Am I understanding correctly the first signs of excessive pressure will be the pancaking, and or cratering of the primer? Where does difficulty opening the bolt fall in line with these signs? Or should I become concerned with definite signs of extractor marks on the brass. Forgive me if my terminology is incorrect.
Ron </div></div>
Usually the thing to back away from with a safety margin is the threshold of short brass life.
If the bolt is hard to lift or the primer pierces, that must be backed away from.
The safety margin is the percentage or powder reduction from the threshold of any real limit.
So you work up. Something goes wrong; short brass life, stiff bolt lift, pierced primer, or anything else.
Then the powder charge is reduced. Determining what percentage of powder to reduce for a safety margin involves many things to consider.
Variations in charges, variations in seating depth, temperature changes, variations in case volume, changing lot numbers of canister powder, variations in bullet weight, shot to shot variation in primer power, the likelihood that the ammo will fall in the dirt, the likelihood the ammo will vibrated thus breaking the powder particles down into smaller ones, hot chamber from rapid fire, how much chance to you want to take with getting short brass life, or anything that is a variable.
I have been getting away with 3% and 4%, but after I saw Komayotch's Re17 temperature variation data of 2%, I think I will step it up to 5% for Re17. </div></div>
Cool deal, understood. That's some very usefull information.