...but nobody has the molds in stock for a 50 cal.
@Kap ,
Very few people shoot a bore sized ball with a patch. Most people go about 0.010" under bore size, using a 0.490" ball. A few of us (myself included) go even smaller, shooting 0.480" balls out of our .50 caliber rifles and pistols, to make loading easier. Track of the Wolf currently has Lee Precision double-cavity round ball moulds in stock in sizes 0.490", 0.495", and 0.500". They also have a six-cavity 0.480" Lee Precision round ball mould in stock. The six-cavity mould blocks come without handles, but the double cavity moulds come with handles installed. So, moulds are available now, although the original question was submitted almost two years ago, and moulds in popular sizes were indeed scarce at that time.
I understand you have a bunch of balls for your .45 revolver. These are probably 0.454" diameter, although some .44 caliber revolvers may use 0.451" or 0.457". There is no reason you could not shoot these in your .50 caliber rifle with a double patch, as described by several of the fellows in previous posts. To reiterate what others have said though, you will probably lose some velocity, and it may not be as accurate as a tighter fitting ball with a proper patch.
Please bear in mind that while .50 caliber is probably the most popular muzzleloading bore size, all rifles are not created equal. The rifles designed for conical bullets and sabots typically have a fast twist (maybe 1 turn in 24" or 1 turn in 30", as examples) and shallow grooves, while rifles intended for round balls have slower twists and deeper grooves. There are some rifles which have around a 1:48" twist which can handle certain conical bullets such as Maxi Balls as well as patched round balls. You can actually shoot patched round balls in any of these rifles, but any projectile with a plastic sabot should
only be shot in a rifle which was made for it. I don't think the sabot would fill the deeper grooves of a round-ball rifle, which would result in gas blow-by, and likely a large amount of plastic residue melted into your barrel. This would make for a nasty and tedious cleanup job.
I know we are not supposed to talk about sabots on this forum, but I think in this case these few words are justified.
If you would tell us exactly what rifle you are shooting, chances are pretty good somebody on this forum will be familiar with it, and can tell you what sort of twist and groove depth you have in it. From there, a better determination can be made on a proper load. You mentioned it is a Traditions percussion, but they make quite a variety of rifles. If you are not sure of the model, maybe just post a photo. Somebody here will surely be able to identify it.
Best regards,
Notchy Bob