I had a few moments to spend in the National Archives recently - and I forgot what a challenge that can be. Timed pulls and limits on quantity or number of records works to hamper the researcher who has only an afternoon to give to the cause. Nonetheless I was able to check six pension records of USCT from Fletcher Post. I am still sorting that information.
So the fruits are that the NA in DC is the mother lode in terms of materials. The nuts are the stringent rules that curb research and access to records. I only note this is due to only a single afternoon to do anything. If you have a few days you end up losing a little time at the start but you should be able to keep the hopper full for the next day, etc.