effect of cold and humidity on accuracy

[aragorn]

Here in southern Ontario we get severe cold in winter and often very humid summers, both conditions likely to result in higher than average air density. Are these conditions enough to effect roundball accuracy to any meaninful extent within the ranges we generally shoot, i.e. under 100 yds? Put another way, should I expect the sights I have just zeroed for 50 yds in minus 20 degrees C to produce much the same results in hot dry summer conditions?

 

[Chickenfax]

should I expect the sights I have just zeroed for 50 yds in minus 20 degrees C to produce much the same results in hot dry summer conditions?

Prolly not. But at 50 yards, you won't be too far off I imagine. Course the atmospheric conditions not only affect external ballistics but also internal ballistics as well as the explosive force of the powder. With humidity prolly the major contributor to the latter. More likely, the largest effect from these extremes will be human physiological in nature -- frozen limbs/digits, etc.

I haven't changed my sights on my 50cal flinter in a year and it still shoots where I point it at 50 yards. I live in Ohiowa. Can't have more extremes in weather than this!!!!
Two days ago, 65F and rain. Today 12F.

Whatcha doin shootin in -12C anyway? Yer CrAzY!!! :youcrazy:

:imo:

 

[madstone]

Strider,
I don't see how you can shoot at those temps! I once tried to fire my flintlock at -25 F and it wouldn't fire. Course I was shakin so badly... The steel would stick to ones skin and I was almost relieved it wouldn't!
You might shoot a little higher at more moderate temps? I imagine the combustion of BP would take place at a rate governed in part by ambient and propellent temp. I used to have a document that illustrated the effects of extreme temp on ballistics. The Army, I believe, did the study.
I'm just guessing but thought I remembered guns shooting slightly lower at lower temps? Some of these folks, in here, will know this, I wager.

 

[flaming canvas]

The difference in air density won't have that much effect on velocity within 100 yards. Probably no more than 10 fps at 100 yards. You will have more shot to shot variation than that.

 

[cayugad]

In Wisconsin we can get some real cold also... the other day (-4

 

[Alberta Black]

Strider

In Alberta we get the cold but not the humidity. This December while hunting in -22 C weather we found that the problem was that the lube we were using froze and was useless. Our mormally accurate rifles lost their zero and accuracy. We changed to Lehigh lube and the problem is solved.



AB

 

[aragorn]

I agree, minus 20 is madness, but if you don't steel yourself to the low minuses C up here then the winter months are pretty well out for shooting. The biggest problem is not so much the air temp but even a touch of windchill, esp when you have to be gloveless for loading and trigger pulling. As soon as I sense any finger numbness I stop, esp as at that point the mind might start freezing up too ... Typically this means no more than ten rounds a session, but at least that's something.
I've had no obvious problems with ignition at low temps, but some of the fouling problems I've had - discussed in my recent thread about swabbing - could be to do with cold.
Anyway thanks v much for these comments, which pretty well confirm what I'd thought.

 

[squirejohn]

Strider - some time ago I posted about a friend whose 42" swamped barrel flinter shot very low in the winter. This however was not attributed to the cold per se but from the stock drying out in the winter and exerting pressure on the barrel.

 

[aragorn]

Squirejohn, can a stock really exert pressure to that extent on a barrel?? Seems incredible to me, but then I'm the learner here. Would that be because it was a swamped barrel, and thus fractionally less rigid than, say, my Pedersoli barrel?

 

[squirejohn]

strider - Apparently so from the responses I got and the consistent results of shooting low year after year in the winter. One other person in our shooting group also had (sold it) a swamped barrel rifle that would shoot off target in the winter. No one else has this problem but neither do they have a swamped barrel. I'm sure there are plenty of shooters with swamped barrels that have no problem at all with different "POI" in the winter vs the summer. Maybe the stocks weren't sealed well allowing differential seasonal moisture content.

 

[Stumpkiller]

Plains style rifles have a relatively squat barrel. It darned well better be stable to justify that miserable weight. It's true a swamped barrel is more flexible than a parallel barrel starting at the same breech dimension. But whether 1/8" of an inch of wood on either side has enough spring to throw it far out of line is debatable. I have long been curious as to how much the choice of wood effects stock stability. Everyone wants the most figured ++++premium maple, which has the wildest grain that's curly and wild. Then look at a carpemter's tools. Wood block planes and levels, both of which determined how the work will turn out for squareness, were made out of cherry. Cherry is very stable in changing ambient conditions. I chose to have my stock for my swamped barrel out of cherry.

Have to wait for POI stability reports.

 

[aragorn]

This is getting a little off-topic and should probably be a new thread, but is there a safety aspect to swamped vs parallel barrels? If a swamped barrel really can be affected by the stock in this way, then is it going to be a little less resilient to powder charges? Or is this in fact not so because the breech end of the barrel which takes the most beating is still thick in a swamped barrel?

 

[Gary]

Conceivably humidity could affect a stock and that would affect how the stock exerts pressure on the barrel. The point of impact on modern guns have been shown to shift when slight pressure from the eraser of a pencil is applied on against the barrel.

Best thing of all is to test the gun after you find the optimal combination of patch thickness, lube and ball weight/diameter. Keep notes as a modern rifleman would do.

Then again, you can carry a smoothbore musket and not worry yourself about scientific data collection. :crackup: I'm sorry, if it's cold, I stay indoors and have pizza delivered. :redface: