First: I have been having fun developing an inventory for my rolling stock, diesels and steam using the Yard Office software program. I highly recommend it to any and all.
As I enter data for each piece of equipment, I am noting the current car weights for reference when I get around to working on each car that needs some attention (most of them!).
With factory-closed cars of various sorts- tank cars, sealed box cars, sealed covered hoppers, etc., how can I add weight to them (perhaps using shot pellets or BBs?)?
For sealed cars like that I use lead shot, such as what you’d get from a shotgun shell, some white glue, a drill bit and some tape. I drill a hole in the bottom of the car then set it on the scale and note the weight. I then put a quantity of lead shot beside it until the total weight equals what I need. I hold the car so it’s tilted over and put some glue inside it so it runs down along one edge then put half the shot in. I then add more glue and set the car so it maintains the angle and let the glue dry. Then I do it again with the car tilted over the other way repeating the process. Once the glue has dried I put a small piece of tape over the hole to keep the errant piece of shot from possibly rolling out and keeping anything from crawling in. Bugs like little out of the way places. I once had a spider climb into a Proto 2000 E6 loco and attach it’s egg sac to the motors commutator (Athearn type motor). I found it when I disassembled the loco to find out why it wouldn’t run. Not pleasant!
My procedure differs slightly in that if I have to cut a hole open in the bottom of the car I’ll do the following:
A. Cut a small piece of overlapping styrene that can be used to cover the hole after the process is finished.
Load the car with BB gun pellet shots until the desired weight is reached. Cheap small plastic funnels from the dollar store come in handy.
Unload the BB pellets into a small tray. (large jar Planters Peanuts lids or other products with big lids work nicely)
Smother them with Elmer’s Glue.
Place your funnel in the hole and load the glue-smothered BB pellets into the car.
Take your scrap styrene cover, apply CA adhesive (superglue), and glue onto the bottom of the car.
Apply masking tape firmly on top of the cover.
Turn your car right side up and gently rock it back and forth to help the BB pellets spread out evenly inside.
Test roll your car on a test track or on the layout to make certain it tracks properly.
In a few hours your car should be ready for full service. Remove the masking tape off of the lid.
I always add weight in my rolling stock (if needed) and adjust the trucks. One thing that drives me NUTS is seeing scale freight or passenger cars WOBBLE anytime they roll over a rail joint or switch turnout frog. I see this too often on YouTube model railroad videos where modelers are running beautiful HO or N scale trains with cars that wobble. Imho, it simply ruins the realism effect.
There are a number of places that you can look for openings in cars
For boxcars and other cars that have a roof walk, gently lift with a hobby knife to see if the roofwalk can be removed. That will open up a number of holes.
For reefers, covered hoppers and similar cars, check if any hatches can be removed without damaging them.
For hopper cars with a steel weight on th slope sheet, replace the steel with lead sheet and paint to match the car color.
For flat cars, gondolas and similar cars add a load to bring up the weight. If still too light add weight to the load.
For cars with a deep center sill, you can glue weights between the center beams.
For passenger cars, if you can get to the inside, there are usually a lot of spaces for the molded tanks and other stuff, these can be filles with lead or other weight. If there is an interior, usually there are spaces that are not visible through the windows where you can hide weight.
If all else fails, the drill and fill method described above works. I give the car a shake to distribute the glue covered BBs.