If a card that isn't a transforming double-faced card becomes a copy of a card with craft, it'll stay in exile if you activate the craft ability. It won't return to the battlefield.

Use the equipped creature's power as the reflexive triggered ability granted by Dire Blunderbuss resolves to determine how much damage is dealt. If the equipped creature is no longer on the battlefield at that time, use its power as it last existed on the battlefield.

If the materials required include multiple objects, you may exile some of them from among permanents you control and the rest from among cards in your graveyard. You don't have to choose all permanents or all cards from your graveyard.

You don't choose a target for the triggered ability granted by Dire Blunderbuss at the time it triggers. Rather, a second "reflexive" ability triggers when you sacrifice another artifact this way. You choose targets for that ability as it goes on the stack. Each player may respond to this triggered ability as normal.

You may exile tokens you control as part of the materials required. However, because they aren't cards and won't stay in exile, any abilities that refer to what you "used to craft" the back faces won't refer to anything.

The back faces of some cards with craft refer to cards "used to craft" it. This refers to the cards exiled as part of the cost of the craft ability of the front face. Those cards are considered to be "used to craft" that permanent as long as they remain exiled and the permanent remains on the battlefield, even if the permanent's controller changes or some of its characteristics change (because of a copy effect, for example.)

If the equipped creature isn't on the battlefield as the reflexive triggered ability granted by Dire Blunderbuss resolves but it had lifelink when it left the battlefield, you will gain life.