Hey all. I’m trying to make a new tenor drone reed. I made one which sounds good but it shuts down when too much pressure is applied. Does anyone know what the cause of this issue may be?
Darth;
I’m going to guess . . . air pressure! 
Sorry, couldn’t resist. Its a pretty common problem, solved in a variety of ways. Some folks swear by a bit of hair slid under the tongue to keep it from closing all the way. Gently “springing” the tongue once (or a few times) will sometimes make it behave - pull up a little bit with your fingernail and give it a little snap.
JVF
Try rolling it between your palms followed by springing the tongue. You are trying to break down the fibers a bit near the bridle. I avoid the hair under the tongue as being a last resort and not so effective on these tiny reeds. Another approach is to lift up the tongue and slide a round toothpick or small diameter wire (straightened paperclip) under the tongue and slide it back some toward the bridle. Leave the tongue propped open over night. Remove this shim and roll the reed between your palms as it will be too open and hard to blow. Then spring it open again. This will settle the tongue into the normal operating range. I assume you are copying a formerly working reed for diameter and length. Some reeds just don’t want to cooperate. A new reed may be in order. I sometimes find I must make two or three attempts on tenor drone reeds to get a successful one. Contact me if you need more cane. I would be glad to make a reed for you if you want to post the drone to me. Make sure the tongue is not too broad.
You might also try putting a strand of human hair between the tongue and the body of the reed (being careful not to force it back too much). This sometimes does the trick.
Reeds require a certain amount of humidity, so a bit of orange peel overnight in a jar with the reed might also help the reed sound out… Springing the tongue would be my first choice