It's of little note at short range, just like temperature, but I'm wondering if any of you folks factor humidity in your calculations for long shots. If so, how; if not, why not? It does change air density after all.
With my 338 Yogi and 300g SMK at 3050 fps if shooting at 2000 yards at a temp of 40 degrees 20% humidity BP of 29.92 and elevation of 900 feet above sea level. I come up with 70 MOA come up. If the humidity in increased to 95%. I would need 69.5 MOA. Then if you increase the temp to 100 degree I come up with 60 MOA.
Crow Mag, what was the source of that calculation? JBM? Or a hand held computer?
700, in jest I say: You quote Uncle Sam's Misguided Children?
You are dot on about the molecular weight. FWIW Dept., Rinker said in his book that humid air was denser, Vaughn said dry air is denser...Vaughn wins without debate.
Guess my question was answered in part by Crow Mag's post, ie. not much effect. On the other hand there is a reason they refer to it as RELATIVE HUMIDITY. The warmer it is, the more effect it must have. Maybe unimportant in cold winter air, BUT, if you're shooting prairie dogs at a mile on a warm summer day...well who knows?
I do not have the performance charts for this but in tropical environments(S.E. Asia) the effect of humidity was potentially as great as Density Altitude on any given day. DA=pressure altitude adjusted for Temp. 4000' DA's at sea level were routine there. In 1970 or so some bright lad let us in on a little secret: 90-100% humidity on hot days could nearly double the figure above, the significance being that a UH-1 could hover at gross weight out of ground effect with a 4000' DA. Doubling that number cut the payload in half OR ensured an LZ marked with black smoke.
I think in the rain you have to calculate the Relative Air index. Kinda the reverse of my question.
Big drops or small?
On a more serious note I've heard from some folks that rain doesn't affect accuracy...a hypothesis I find vastly amusing. I've read two articles on the subject that were based on both simulated and actual rain. In the Sim. evaluation which had fall rates on the order of 1"/hour it increased dispersion on the order of 3-5 times with a 7mm bullet as I recall. The actual rain test was with light showers to drizzle and and had no measurable influence at 100 yards.