Humidity v Trajectory.

[JeffinNZ]

Hi all.
I was getting in some practice for the late Oct. rondy o'here at the weekend when I documented what I had suspected for some time. I knew air density affected bullets in flight but this gave me real readings.
I live on the dry east coast of the South Island of New Zealand. Our humidity is generally 40-60%. When I was shooting my 2 round ball .40 cal pieces on the west coast where the rainfall in significantly higher and the humidity closer to 80-90% there was a 2-3 MOA difference in the point of impact at 50 and 100 metres. The shots all landed lower on the targets to that tune.
Probably no great revalation to those how are in the know but it is worth considering if you are moving outside your usual area to shoot. :m2c:
I have made recordings and adjustments accordingly.

 

[Ohio Joe]

Your observations are correct. Years ago when I lived in Ohio and shot competition at 800+ feet above Sea Level with high humidity, my rifles were zeroed right on at 50 yards.

When I moved to Nebraska, in an area almost 4000 feet above Sea Level with low humidity, all my rifles shot 4 to 6 inches high at 50 yards. I remember checking my sights thinking that they may have gotten jarred and moved? They didn't. The fixed sighted rifles came out and I know they could not be moved. They too shot 4 to 6 inches high at 50 yards. Sight adjustments, and new sight changes began.

 

[Keith]

I believe the humidity doesn't effect trajectory much. At least not that much. What humidity does effect is the gun's wood. The wood absorbs moisture or loses the moisture as the case might be. This causes a change in the wood and how the wood brings pressure on the barrel. The barrel harmonics can change. You know the barrel has a vibration when it is fired right?
No matter how well you finished the stock it will be effected by the humidity.

 

[Deadeye]

I believe Keith is right, something going on besides the humidity. My guns are zeroed at 6000 ft. and about 10 to 15%humidity. I compete sometime at 10,000 ft and sometime at sea level and all sorts of humidity and I don't see any difference. Just my observations. :results:

 

[JeffinNZ]

HHHMMM.
I see your point and if it was just the full stock Haines rifle I would agree however the half stock Wesson with a 2 piece stock suffers the same variations. :hmm:
Still, its academic once you know where the bullets are landing and can allow for it ah?