Here are the fixed reactions, with the various changes outlined below so you can understand exactly what I changed and why.
[REACTION:MAKE_AMMUNITIONS]
[NAME:prepare ammunition]
[BUILDING:GUNSMITHERY:CUSTOM_A]
[REAGENT:A:50:AMMO:ITEM_AMMO_BULLETS:INORGANIC:LEAD]
[REAGENT:B:150:POWDER_MISC:NONE:INORGANIC:GUNPOWDER]
[PRODUCT:100:50:AMMO:ITEM_AMMO_AMMUNITIONS:INORGANIC:LEAD]
[SKILL:BOWYER]
[REACTION:MAKE_BULLETS]
[NAME:make bullets]
[BUILDING:GUNSMITHERY:CUSTOM_B]
[REAGENT:A:150:BAR:NO_SUBTYPE:METAL:LEAD]
[PRODUCT:100:50:AMMO:ITEM_AMMO:BULLETS:INORGANIC:LEAD]
[SKILL:BOWYER]
[FUEL]
[REACTION:MAKE_GUNPOWDER]
[NAME:make gunpowder]
[BUILDING:GUNSMITHERY:CUSTOM_G]
[REAGENT:A:1:BOULDER:NO_SUBTYPE:INORGANIC:SALTPETER]
[REAGENT:B:1:BOULDER:NO_SUBTYPE:INORGANIC:BRIMSTONE]
[REAGENT:C:150:BAR:NO_SUBTYPE:COAL:CHARCOAL]
[REAGENT:D:1:BOX:NONE:NONE:NONE][BAG][EMPTY][PRESERVE_REAGENT]
[PRODUCT:100:1:POWDER_MISC:NONE:INORGANIC:GUNPOWDER][PRODUCT_DIMENSION:150][PRODUCT_TO_CONTAINER:D]
[SKILL:BOWYER]
[REACTION:CONSTRUCT_MATCHLOCK]
[NAME:construct matchlock]
[BUILDING:GUNSMITHERY:CUSTOM_M]
[REAGENT:A:150:BAR:NO_SUBTYPE:INORGANIC:IRON]
[REAGENT:B:1:TRAPPARTS:NO_SUBTYPE:INORGANIC:IRON]
[REAGENT:C:1000:THREAD:NO_SUBTYPE:ANY_PLANT_MATERIAL:NONE][DOES_NOT_DETERMINE_PRODUCT_AMOUNT]
[REAGENT:D:1:WOOD:NO_SUBTYPE:NONE:NONE]
[PRODUCT:100:1:WEAPON:ITEM_WEAPON_MATCHLOCK:GET_MATERIAL_FROM_REAGENT:A:NONE]
[SKILL:BOWYER]
[FUEL]
And here is a new gunpowder entry that might work a little better for you
[INORGANIC:GUNPOWDER]
[USE_MATERIAL_TEMPLATE:PLANT_POWDER_TEMPLATE]
[STATE_NAME_ADJ:ALL:gunpowder]
[DISPLAY_COLOR:0:0:1][TILE:'#']
[SOLID_DENSITY:600]
[MATERIAL_VALUE:20]
First thing you need to do is fix the item subtypes for your bullets. It should end with INORGANIC:LEAD, not LEAD:BULLET. You also have an extra NO_SUBTYPE in there on your ammo reagent.
[REAGENT:A:50:AMMO:ITEM_AMMO_BULLETS:INORGANIC:LEAD]
[PRODUCT:100:50:AMMO:ITEM_AMMO_AMMUNITIONS:INORGANIC:LEAD]
The next thing you need to do is increase the reagent number to 150 for the gunpowder in your make ammunitions reaction and the bar in your make bullets reaction. This is because it is a powder and you have set it's [PRODUCT_DIMENSION:150] (this is right, but when you work with powder or bars you need to increase the reagent amount as well.
[REAGENT:B:150:POWDER_MISC:NONE:INORGANIC:GUNPOWDER]
[REAGENT:A:150:BAR:NO_SUBTYPE:METAL:LEAD]
You will also need to increase these reagent amounts for your bar reagents in both your make gunpowder and construct matchlock reactions as well.
[REAGENT:C:150:BAR:NO_SUBTYPE:COAL:CHARCOAL]
[REAGENT:A:150:BAR:NO_SUBTYPE:METAL:IRON]
Also since you don't want anyone making a million guns because they have a big piece of cloth, you probably want to add [DOES_NOT_DETERMINE_PRODUCT_AMOUNT] to that. You don't need to worry about the other three reagents since they will never come naturally in a stack greater then 1.
[REAGENT:C:1000:THREAD:NO_SUBTYPE:ANY_PLANT_MATERIAL:NONE][DOES_NOT_DETERMINE_PRODUCT_AMOUNT]
You are also missing your bag for your gunpowder making reaction. You have the TO_CONTAINER bit right, but you don't specify the container in your reaction.
[REAGENT:D:1:BOX:NONE:NONE:NONE][BAG][EMPTY][PRESERVE_REAGENT]
[PRODUCT:100:1:POWDER_MISC:NONE:INORGANIC:GUNPOWDER][PRODUCT_DIMENSION:150][PRODUCT_TO_CONTAINER:D]
Lastly you can't make new professions, so you will have to make do with old ones. This will also fix your instant reaction problem, as it will be an actual skill used. I suggest using the bowyer skill, so [SKILL:BOWYER], in your reactions as it is the most similar.
There were also a few typos here and there that I took the liberty of fixing. Note that your current gunpowder template will be stored in "food" stockpiles under the powder category.