The power of a column or jar of primers is something not to be complacent about. I have heard of a Dillion press that was fragged, from the people who saw the pictures, after a reloader tried to prime a small primer 45 ACP brass with a large pistol primer. This is a picture of after a column of Federal primers that went off in a Lock and Load press.
There has to be very good reasons for factory primer packaging. It is clearly there to keep the primers separated and I believe it must be to help prevent flash over, buffer the primers from shocks, and to keep primers from banging into each other.
What you have done by pouring loose primers into a jar is very dangerous.
In so far as heat, I found data on the web for the older chlorate primers, those primers dud after extended exposure to heat. I have not found similar for lead styphnate but I have no doubt that heat over 140 F for a year or two will cause duding issues.