Will single digit temperatures hurt an 85 year old gun?

I live in Canada. Lots of single digit temps. So I sure hope not!

Humidity is more important than temps.

Cold tempratures wont affect the gun but the performance of cold soaked ammunition loaded with slow burning powders such as Blue Dot will be degraded.

Much depends on the way the locks are oiled. Too much of lube, or the lube which goes solid at the temp, and you might have dry fires. Age doesn't have anything to do with that.

On the contrary, in real freezing cold, say below -25 C., I'd much rather be shooting a hammer gun than a modern semi - if it does have lube problems, you've been had for the day, while a dry fire in a hammer gun is easily checked by re-cocking the hammer and having another go. Most shells which won't fire due to weak lock will go off the second time.

Ammo, as noted above, is affected too. Basically, when it's real cold, most plastic wads have problems, either with breaking in the barrel or, most commonly, with obturation problems due to being too stiff. Fast powder and fiber wads (felt is best) are the way to go.

I was thinking that the old lacquer could shrink and crack.
Also, the receiver metal could shrink and put stress on the wood.

An instance of this "Fact" is what turned me OFF to low pressure loads of 7625. This in a load that was between 7K & 7.5K. I can only imagine that had it been down in the super low range of 5K - 6K the charge would not have cleared the barrel.

Not sure about the laquer.
But I know folks who do their shooting in the Arctic, with temps as low as -40C, and they don't report any metal-wood shrinkage issues.
You're advised, however, to avoid the warm-cold-warm-cold temp changes to your gun as much as possible. The folks I mentioned above, while in tundra, keep their guns outside at all times.

I've never had any problems with mine in the cold. I suspect shooting them a lot in triple digit heat is actually harder on things like lacquer and wood.

Best,
Ted

not as much as it does an 85 year old gunner

If the paint on your house doesn't fall off during cold weather, the finish on your gun should be okay.

I would not have thought this on my own, but now that you've said it, it makes perfect sense.

I think right in there with cold compatible loads is good lubricant compatible with the temps. I know one of my Parker was full of 100 years worth of oil and grease of unknown types. I think it would have failed to function in extremely cold weather.

Being an "EX" carpenter from northern MN we would often work in -30 to -40 weather and at those temps driving hardened nails (concrete nails) we would experience metal chipping off the face of the hammer, it never happened in warmer weather. Also welds would break much easier on the snow removal equipment when it got down in that temp range.

It wasn't too long ago that one of the rifle manufacturers had a problem with barrels splitting in extreme cold, can't remember the details though.