I do not shoot much BP, but when I do it is out of traditional , side hammer, cap lock rifles. Pyro does not ignite well for me with std caps, in cold weather and hunting conditions.
Traditional is all I use. I never had a problem with Pyro in cold weather hunting. I'm a lil further south than you but it still gets pretty cold. We've even had snow the last couple of years. That's a new experience, hunting in snow.