I started flintlock hunting in 2013 with a .50 T/C Hawken flintlock. I've killed a deer with it each year since then, needless to say I'm hooked.

My son is 11 years old, and has been hunting with me for a few years now but we can only have one gun between us. This coming deer season is the last season we'll have to carry only one gun. I have a Traditions .50 flintlock but it's pretty much garbage, though it's light and would make a decent gun for him.

I'm thinking about getting another flintlock and letting him use my .50 when the time comes. Is there enough of an advantage when hunting to go with the .54 over the .50, and stock different roundballs etc.?

Yes, just because. Then you'll need a .58

My safe is full. And I'm not buying another safe. My collecting, just to collect, days are over.

But seriously, is the .54 that much better than the .50?

I like the .54 better than the .50 but the .50 is the industry standard.  .54 is a bigger, heavier ball with more punch. If streamlining your supply line is a priority stick with the .50. What you don't know you can't miss.

Back in the day, if a mountain man moved out west with a .45, he soon wanted a .50 just for the improved terminal ballistics, and if he had a .50 he wanted a .54 for the even better terminal performance.

The only real advantage of smaller calibers then was the ability to make more ball per pound of lead, but the big break there is between 45 caliber and 50 caliber as you can get 52 .45 balls per pound compared to just 38 for a .50" ball.  In comparison you can get 32 54 caliber balls per pound, so you're giving up very little moving from 50 to 54 in terms of lead weight carried. However you gain a lot in terms of effectiveness with the larger caliber, particular if you are shooting traditional round balls.  54 caliber is essentially the sweet spot for velocity versus weight of ball in a round ball muzzle loader.

If you move to a minie ball or maxi ball, the .54 still has an edge over the .50, but both are left in the dust by a .58.  Personally, I think a Remington Zouave is near perfect for traditional hunting with a traditionally designed muzzle loader as it is reasonably light, reasonably short, accurate, and the terminal ballistics of a 500 to 525 gr traditional minie ball at 100 yards are awe inspiring.  

Where the .50 reigns supreme is in the relatively recent sabot bullet loads.   When using a sabot and a pistol bullet, the .50 seems to deliver better performance than a .54.   But personally, I look down on that combination for "traditional" hunting the same way I do an inline muzzleloader, and in particular a scoped in line muzzle loader.

I'm probably a throwback but I feel traditional hunting should be just that - hunting with a traditional muzzle loader design, using iron sights, and using a solid lead projectile that is either patched or interacts directly with the bore.

I agree, nothing but PRB for me out of a flintlock.

If I were to go on a blackpowder elk hunt or something, I'd consider a more conical bullet to get more mass out of the bore.

Just get a minie rifle.

Since you are wanting/needing another flintlock, you may want to consider a smooth bore.  A trade gun in .62 caliber (AKA 20 gauge) would work well for most any hunting in the lower 48.  Use a .590 to .600 round ball for big game and proper load of shot for anything else.  For wads, you can purchase 20 gauge components (felt and card wads) or you can make your own.

You can either use a patched round ball or you can use a card over the charge, followed by a lubed felt wad, then the bare ball, and another felt wad.

I just thought I'd throw out another option.

I have a TC Thunderhawk inline and a TC New Englander caplock that are both in .54.  My boys have .50 cal inlines and caplocks.

Deer can't tell the difference between the .50 and .54.

I don't see the advantage of buying the .54, except I had mine before the boys started hunting and I got a much better price on them because .50 was all the range at the time.

If I were to go it all over again, all 3 of us would have .50's.