Effects of humidity on pressure?

[HTDUCK]

Question for the brain trust,trying to make rhyme or reason of what happened yesterday.

I am working up loads for a Savage 110 in 7Mag.

Two weeks ago it was 104 degrees and humidity was around thirty percent .Up to 65 grains of RL22 topped with a 160 AB, no pressure signs and decent groupings,just not quite what I feel the rifle is capable of.

Back to the reloading bench.

Same lot of brass, all sorted by weight.Prepped the same day.Same box of primers ,bullets ,same can of powder.
I started playing with seating depth. OAL of original group was 3.355.

Test loads were 65 grs at 3.350 ,3.345 3.340 etc.

I had no pressure signs two weeks ago. Yesterday I could lift the bolt but not extract the cases.

Yesterday was 102 with humidity levels in the 80 percent range.

Is the humidity the culprit?
Yeah I know,August in Texas isn't the ideal time to be doing load development work but a fella has to make hay while the sun shines.
November will be here soon,just not soon enough.
Howard

 

[barthowes]

did you start back at the minimum load after changing seating depth.I would say that adjusting this is what gave you your pressure sgns. Same load at different OAL = different pressure.

 

[DrMike]

To my knowledge there has not been a correlation between pressure generated and ambient humidity. The more likely culprit is neck length, shoulder position, etc.

 

[SJB358]

Yeah, I would concur with Mike on a possible length/shoulder issue. I shoot a ton in the humidity of Va Summers and haven't experienced any issues with my loads going crazy. I pretty much development all of my loads in the hot/humid days (only time I have to shoot). I figure if they are safe there, they should be safe anytime/anywhere else. Scotty

 

[JD338]

Changing the COL will affect velocity/pressure.

JD338

 

[chet]

on a side note, I've always felt good about developing loads in the summer as it ensures that they'll be safe in the fall/winter.

 

[Antelope_Sniper]

I started playing with seating depth. .


Howard

This is your Culprit.

 

[HTDUCK]

Ok I admit I caused my own own problem. I was mistakenly under the impression that as seating depth got longer the pressures would rise.

Back to the bench I go.

Thanks.
Howard

 

[Guest]

Howard,

You can change pressure both ways. Whether it increases or decreases is dependent on several factors. First, if you start out very close to the lands, it is likely that shortening the COL will reduce pressure to a point, as your start pressures will be lower without the resistance of the rifling for the initial movement of the bullet. But, at some point, you start impacting case capacity, and when you reduce case capacity (volume) you increase pressure. So, conversely, if you start short, lengthening the round will decrease pressure to a point, then increase it as proximity to the lands shrinks.