Dropping barrel proof

[Ridgeback816]

I am wondering is this is normal(ish), in my Distilling evolution last year I bought a five liter oak barrel. I had a first fill of rye whiskey that sat for 4.5 months. It entered into the barrel at 65 percent it came out at 58 just over 3 liters. I have since filled it with bourbon at 57 percent that sat for 7.5 months and that just came out at 49 percent at just over 3.5 liters. I was hoping to age this in glass for at least 4.5 more months but is my proof to low? Should it go back into the barrel and artificially create and environment to raise the proof that way? (Not even sure what that would look like) This is it for my small barrel and will be upgrading to a 5 or 10 gallon barrel soon is this a small barrel problem or an environmental problem?

[Sporacle]

"Angels Share" different vapour densities mean you lose certain portions first.
Losses in small barrels have been seen to be a problem, I've got small barrels in my Solera set up and don't really notice it though.
Just remember the environmental thing is what ages your stuff

[Saltbush Bill]

Depending on climatic conditions barrel contents can increase or decrease in ABV.
Amount lost to angels also varies depending on temp humidity and other factors.
Both are quite normal.
Lose from smaller barrels is usually more and faster.

[IAmPistolPete]

You didn't say what volume you put into the barrel in either case, as the more headspace the faster the evaporation. But assuming you put in close to the 5L top it is still pretty normal for a small barrel. As SBB said the loss or gain in ABV will depend on the environment it lives in. The staves in a smaller barrel are thinner & therefore more likely to evaporate your spirit quicker. A humid environment will evap the alcohol quicker, lowering the ABV & a dryer env will evap the water[& but some alcohol] quicker but usually raise ABV slightly. Higher temps [65F+] will increase the volatility & lower will slow things down.
As far as what to do with your current stock, only your tasting will tell you. You will get "barrel influence" quicker but not necessarily as much "aging" with it. Bottle or jar aging will continue to smooth your spirit. You will see as you increase barrel size, there is less worry.