What size tubing for 1/48 machine gun barrels and where to get it.

Which gun? I'm using hypodermic needles for some scratchbuilt M3 grease guns in 1/48. I don't know the gauge - I just use whichever looks right. Definitely smaller than 14. I save those in case I need to give someone a Needle D.

I also have extremely fine brass tubing I ordered online I use exclusively for necked spent casings. One diameter inside another looks far better than cut off pieces of sprue. I wish I could tell you the brand but the stickers have long since fallen off the plastic tubes. If you find it online your best bet, as with needles, is to get a good supply of several sizes.