The Infantry Museum at Benning is a great idea, and the kids can go to Ranger Joe's afterward to get stuff. Or, if you want to travel some, look into the Airborne and Special Forces Museum at Ft. Bragg.
Depending on how hearty and rough and tumble your group is, a winter survival camp out might be a lot of fun. It's take a good deal of logistical support from the Scoutmasters, but it's doable.
For something different, look at local theater groups and see what sort of holiday productions they have during the winter. About 10 years ago, the council I worked for had a fundraiser for Camp at a local theaters production of A Christmas Carol. I was surprised at how many older scouts attended, and they really had a great time. You might be able to convince the production company into giving the kids a guided tour of the theater, and/or hosting a Question and Answer period with the cast and crew after the show.
If hiking is getting old and stale with the guys, but you still want to keep it as a part of the program, change the way you hike.
* Let Them Do It. Let the older scouts, under the leadership of the Senior Patrol Leader, plan the next hike. Have them choose a location, a destination, plan a route, make all the arrangements. It's usually interesting to see what they come up with.
* The Big City. Urban hiking in Atlanta can be really exciting and fun if you're Troop is from outside the perimeter. You can make use of MARTA, and teach the kids how to read a train and bus schedule, and get across the city safely (Yes, this will require some oversight to stay ut of some of the unsavory area's of the city). Choose a few spots n the city, the Aquarium, World of Coke, Turner Field, and have the kids navigate to those points. Close the day off with some sort of big time activity, like a concert or a show, or something.
You can even combine those two ideas, and let the older scouts plan the city adventure.
Look into a day of shotgun shooting or muzzleloading at a local range (Tom Lowe Trap and Skeet here in Atlanta is open year round).
On shooting sports and firearms activities, make sure you check the current
Guide to Safe Scouting for the most recent policy on firearms use. I know that when I was a Range Officer for my old local council, the regs were that Boy Scouts were limited to using only .22 single shot, bolt action rifles (bolt action rifles with a higher capacity were allowed, but only if used as single shot rifles), 12 gauge shotguns (or smaller), black powder rifles and shotguns of .50 cal or less, and air rifles and BB guns. The Venture program had no limits beyond what was legal in your area.
Now, you could take your chances, and it's most likely nothing will go wrong. If that's the case, great. But, if something does go wrong, following the GSS will make sure you are protected by the BSA's liability coverage.
Lastly, thank you for being involved in Scouting. I'm an Eagle Scout, a former volunteer, former professional, and former summer camp staff member. I appreciate every volunteer who gives their time, energy, and resources into making a kids life better. Keep up the great work, and if you need any advice, drop me a line anytime.