This forum is some of the only information I can find on sidekicks and after searching it, I still have questions. A buddy of mine offered to sell me his sidekick, 3-9x40 Simmons scope, blue, wood, for $100. It's not in bad shape but its been used and can use a good cleaning. Is that a good price or would I be spending too much? Also, he said the barrels are interchangable, with the recent change in laws that let you shoot a 444,45-70, etc, I'd love to be able to convert it to a single shot 444, but couldn't find anywhere that said that can be done and couldn't find any barrels for sale. So is swapping the 50 cal barrel out for a 444 even possible? Thanks for any help.
Abear - First of all welcome to the forum. Let's answer your questions, one at a time.
A Sidekick, with a 3-9x40 Simmons scope, blue, wood, is in my opinion worth more than the $100 your buddy is asking for. You say it's used (which is expected), and not in bad shape. The question is; what shape is it in? Does it have rust, is the bore clean, has the gun been taken care of? I would recommend that you have him remove the breech plug, and check out the bore, to make sure it's in decent shape. It is important that the breech plug can be removed. Make sure the gun locks up properly. Then check to make sure that it doesn't have major rust. If needed, the breech plug tool is available from H&R, or you can buy/get a replacement from one of our members.
Like "YRUpunting?" said, if you don't like it you can probably sell it in the classifieds, and make a little money. I purchased mine, in the H&R classifieds, also with a 3x9 Simmons scope, and paid more than double what your buddy is offering to sell one to you for, but mine is the stainless version, and was in almost brand new condition.
As "mechanic" said the Sidekick is a muzzle-loader only. Your buddy may have been confusing the Sidekick with the Huntsman, which is also a muzzle-loader, but the Huntsman can be fitted with shotgun, and low pressure barrels (mostly pistol caliber barrels).
Since it's your buddy, after examining the bore, why don't you ask him to let you shoot it? See if you like it. Personally, I think you'll be hooked. If it's up to your standards, I would not hesitate to buy it. Just be careful, being an H&R owner is very addictive.