Do your groups change when it's HOT

[recurve]

I do most of my range work in marchwith it's Cool/cold & dry air ,like hunting seasons and  range  all to my self .  I went today and things seamed different ,weather HOT and thick wet air(not rain but close)

I could not get the groups I should have.  Does the heat affect your groups? My mutton tallow might not work as well in hot weather, the  patches looked good, might need to add something , or should I  let the barrel cool down before next string of shots?

[Darkhorse]

My grouping stays the same hot weather or cold. I've shot my barrels until they were very hot with no observable change in group size. My pin holes are well elongated to handle the movement of a hot barrel.

[Daryl]

No change, hot or cold, flint longrifle with pins or percussion 1/2 stock with wedge.
No elongation of pin holes that I can see.

[Marcruger]

I don't think I can load fast enough to heat up a barrel on a cold day.   

[JohnnyFM]

I have not experienced any noticeable change in point of impact with my flintlocks regardless of weather or season.
Paper punching, steel ringing, and wood chuck killing in the heat of summer.  Some more plinking, squirrel shooting, and deer killing in the fall and winter.

Some things I would consider if I had your dilemma.
Are groups same size just different points of impact?
If yes, could be barrel binding as already suggested or simply sun position at different times of year affecting sight picture.
If one group consistently larger than the other that could be anything from lube performance/changes to extraneous range distractions and many things in between

Your mileage may vary.

[Bsharp]

Heat doesn't seem to bother like the change from dark shade to bright sun light.

[hanshi]

What Bsharp said.

[Bob Roller]

I change in cold weather to warmer clothing. Never gave weather much thought when shooting but
I do agree light changes can wreak havoc.
Bob Roller

[bob in the woods]

Did you notice any change in the fouling ?   Build up ?   

[Daryl]

I never see any change in the fouling, because it does not build up.
Each time I load, that seems to clean the barrel of the previous shot's fouling
thus the bore's condition, shot to shot, is non-changing.

This includes shooting in hot dry climates such as happens at Rendezvous BC some
times. The very worse was 110F to 122F and 7% humidity, back in 2006, in Kamloops
BC.  Again, no problems with loading for a 22shot trail walk, but even in the tin in the
possible's bag, the lube almost dried by the time the 'trail' was finished. A little spit and
the patches were wet enough to work just fine.

[Jeff Murray]

You inferred extreme heat and humidity in your question.  "Damp" powder could affect results.  The combo of heat and humidity could also affect your concentration.  When the "Misery Index" (temperature + humidity) goes above 160-170, it gets a little harder to be comfortable/relaxed while shooting.

[alacran]

I have shot in matches where the temp was 110 degrees F. That was in Mesa AZ. Most of our summer matches were 100 degrees or more. The humidity between May and the middle of July averaged about 10%.
 Fowling becomes a problem in such a dry clime. So either you have to use a very wet patch or swab between shots. My groups were not influenced by the heat in any noticeable amount. I have also shot matches or plain practice when temps were below 20 degrees F.  I have done this in dry as well as humid climes. Humidity can change things but light conditions seem to be more significant when shooting open iron sights.
All that being said long lay offs in shooting will be more detrimental to your ability to group consistently than all of the above.
To me along lay off, would be two weeks without shooting something.

[far55]

Mad Monks reply in this forum under the heading of Flintlock Cleaning may have some bearing on this. Dont know myself, but just saying.  Roland