decarboxylation before making brownis

Can I put a refracory box with butter and weed into the oven to decarboxylation the weed. How much degrees shall I put the oven on? And for how long will I let it simmer in the oven?

You could do that but your brownies will taste horrible. My favorite way to make cannbutter is to just boil a big pot of water, add a couple sticks of butter, add your bud, turn down heat to a soft boil and let it go for an hour or so. Strain it and put the water in your fridge. After a few hours the butter will solidify at the top and you can scoop it off and use it in your brownie recipe as a substitute for vegetable oil.

Exactly what Bugeye said Try a quarter ounce per stick of butter. Grind it up real fine, and boil it with enough water to keep the marijuana from hitting the bottom of the pot and burning. Longer you cook it, the longer your butter has to pull all the goodies out of your marijuana

I finely grind my trim/bud and place it on a cookie sheet, then put it in a pre-heated oven at 300 for 15 min to decarboxylate it before starting the infusion process. This seems to increase potency.

The whole point to decarboxoloyate your product before starting the infusion process is to convert the THCA(non-psychoactive) to THC(psychoactive). Doing this before you make the butter will increase the potency of the finished product.

I have even been experimenting with mixing decarboxylated and regular trim/bud together, and it seems to make the effects even stronger.

But if you are making brownies, the brownies will be in the oven at 300 for 15 min. will you still heat the weed before or is it enought once with the brownie mix?

You can decarb by drying your weed before using, by heating it, or by pressure (usually used on hash). So if you are cooking with dried weed it is already active. If wet weed it will need heat. Boiling it to make the butter and then cooking it in brownies will certainly do the job. At what temp and duration you need to maximize psychoactive properties I do not know.