Temperature and load

[William Worth]

This may have been covered elsewhere, but here goes.

At  higher ambient temperatures, everything else being equal, it seems like a load reduction is in order, in all calibers, but perhaps more so in the larger calibers.

Do others concur with this observation?

[Daryl]

We all shoot he saem load, no matter what the temperature. Pressures aren't critical with BP, however if very serious about target shooting not only a load change, but a lubricant change might be necessary. I know the modern guys go by atmospheric pressure when changing loads in their modern BR rifles.  I'm not sure they change for temperature, just atmospheric changes.  Needless to say, there needs to be a ton of experimentation done to find what changes to make and how much, not to mention if the particular rifle needs it. Same goes for black powder rifles - assuming here we're talking about a style of shooting that might show a difference. That might be the clincher in, can you prove it makes a difference? The BR boys can, but they're talking about only a few thousanths of an inch difference over 5 shots.

[Dphariss]

Compared to British Cordite which was pretty heat sensitive from what I have read, BP is nearly immune from heat induced ballistic changes. Thus reducing the load is not necessary for hot weather.
Now if its -30 and you compare it to +100 you will likely see a change in the velocity. Assuming the barrels are both at ambient temperature. This would likely be due to heat loss to the barrel reducing gas expansion slightly. But even then the reduction/increase will likely be small.

Dan

[Jerry V Lape]

 But on really cold days the same load may produce a little more pressure because the hole in the barrel is smaller.  This could result in a higher velocity .   I have extensively tested for this difference in bore size and find it occurs and is significant .  Further in very cold weather only brass balls retained their coefficient of cohesion sufficient to be useful to obtain consistently measureable performance differences.  None the less, with a steady hold I am able to get one hole shotgroups in the snow out to about one meter .   

[Daryl]

Jerry- I found the point of impact at 100 yards, along with the accuracy to be identical down to my testing at -40.  I also found it was much easier to just use paper ctgs.  At that temp, the springs are in jeopardy - some have broken theirs and it's a good idea to pack spares.  That was iwth cap guns. I wonder if those temps would have a breakage effect on flints?

[J.D.]

But on really cold days the same load may produce a little more pressure because the hole in the barrel is smaller. 

I know that feeling. The pucker factor associated with really cold days significantly affects my shooting too.