There is a gun shop/hardware store in Lynchburg on Lakeside Drive that has been there for at least 20 years. It's been a very long time since I've been there, but it was the first shop I ever visited.
Regarding your presumed route, I used to travel between Lynchburg and Baltimore with some frequency and always found Route 29 to be a more enjoyable drive. Provided you can avoid 95/495 anytime around rush hour, it'll be faster as well. Then again, you may have other reasons for taking I-81, but I thought I'd give my two cents.
Assuming you’re driving US 29 to get down there I’d stop by Clark Bros. in Warrenton, usually a good selection of standard capacity magazines. I normally stay in Roanoke when down that way- there are some shops along US 460 between Lynchburg and Roanoke I see frequently but haven’t stopped in. If you go down to Roanoke they have a Sportsman’s Warehouse big box store, also good for mags.
If driving 70 directly to 81 then south there’s several around Martinsburg/ Inwood or or 340 to 7 to 81 you’ve got options in Winchester and Harrisonburg. All depends on the route.
Thanks for the info. The couple we are going with said 81 was more consistent for them when they've travelled this way. Also trying to avoid DC on a Friday afternoon.
If you do happen to be on 29 on the trip (maybe the return) and you are looking for a meal stop, check out the Pig and Steak Restaurant in Madison, VA. It is just off the highway and had great Barbeque.