Do they even make condoms that small to fit lol? I wouldnt use a condom, thats just plain nasty and smelly. I'd use a balloon that fits snug over the barrel. If its raining or snowing, why would the barrel be pointed up in the first place? I hunted this season in light rain with my flintlock and didnt bother with covering the muzzle. I always carry it with the barrel pointed down. I'd pay more attention to the breech where your cap is. No reason to carry the rifle with the barrel up while in rain or snow.