Temperature vs humidity

[lefty315]

I know both temperature and humidity can cause pressure to rise in a given cartridge, but which one by itself has more effect?

I recently worked up some loads for the 300 WSM. The temp was about 70 but humidity was low. Today I took the same load out with cooler temps but 93% humidity. Results...sticky bolt.

 

[Charlie-NY]

I find it hard to believe that a humidity change takes place inside of a properly loaded cartridge. Obviously temperature does.

It would seem that something other then the elevated humidity caused the "sticky bolt".

 

[DON]

different lot of powder maybe? Was the load developed in colder temps and not shot in warmer temps.?

Don

 

[lefty315]

Same lot, same cases, same scale. Loaded this morning and fired within 2 hours. Load was developed on a 70 degree day, today it was 55-60.

 

[Horsethief]

I don't think the humidity had anything to do with a sticky bolt. The case was either exposed to more than usual pressure or there is some crud in the chamber, maybe even on the cases.

Air temperature will have more to do with exterior ballistics than the humidity, especially if the powder is not temperature resistant. Shoot a load at 40 degrees and then shoot the same one at 80 and you're going to have more velocity with the 80 deg load, all other things being equal. A 20 percent drop in humidity can make up to an inch difference in bullet drop past the zero range of the scope.