Buckhammer74,
Not to confuse you any more than you are, but there is another option. You could buy either the 20ga Ultra Slug Hunter or the Huntsman (instead of the Sidekick), then send in the receiver for the other barrel.
I have both the 20ga Ultra Slug Hunter LE and SS .50 caliber Huntsman and both are the finest Lower Michigan Whitetail rigs you could ever ask for. I have hunted Whitetails in the "Shotgun Zone" for over 30 years and have owned just about every shotgun/slug gun out there. I also own 7 muzzleloaders (3 Whites, 2 Knights, 1 T/C and the NEF Huntsman) and the NEF is the least expensive, least fussy and most accurate of my .50 calibers. I own or have owned slug guns in Browning, Ithaca (2), Remington (3), Mossberg, Ithaca/SKB to name a few and the 20ga Ultra Slug Hunter LE is my first choice with the shotguns.
With the new High Performance 1800-2000+ FPS saboted slugs on the market, the 20ga will keep up with the fastest muzzleloader loads out there. The bullets are in the 250-260 grain range and are plenty medicine for the whitetail out to 150 yards and a little more if one practices and knows the trajectory past 150. The bullets have enough energy to 200 yards, but only for the marksman that can place his shots into the boiler room at those distances.
So, if you would like ONE receiver, 20ga Ultra Slug barrel and .50 caliber muzzleloader barrel I would buy the Huntsman and send it in for the 20ga Ultra slug barrel. I think you will find that the triggers are much better on the Huntsman/Sidekick than you will find on the Ultra Slug and that is why I would recommend getting the Huntsman first. That way you will have your muzzleloader and if you wish to get the Ultra Slug barrel you can send it in or just buy the gun later.
I have a cantilever slug barrel and it is quite accurate, but these new slugs in that gun are brutal in the recoil departmant, not to mention hard on scopes in an autoloader.
I love hunting with my muzzleloaders, but sometimes it is nice to just drop in a slug and go hunting. Good luck in your decision, but if money isn't an option, I'd get both too. :grin:
The simplicity of the single shots are what really trips my trigger!