Low Temp Oven

Forgive me if this is not the right forum to post this question.  My husband is a gunsmith, and needs an oven that can stay at 250 degrees for 3 hours to cook the paint on the guns.  It seems that a rocket oven is much too hot for what he needs. Does anyone have any suggestion for a (White) oven we can build outside that would work in this application?

Offhand, it sounds a lot like a tempering oven that a knifemaker would use to precisely adjust the hardness/ductability of high carbon steel. There might be a lot more online information if you search for that.

Are you set on using wood/charcoal? That's a challenge -- it would be hands-on through the whole time. Would some propane be allowable?

I believe most high quality tempering ovens these days are electric, with excellent "smart" PID industrial control thermostats to ensure consistent results.

I've kept my rocket oven at 350F steadily for an hour or two.  It's helped by the fact that I have a couple of pizza stones in there, so the mass helps hold the temperature steady.

I've found that one bigger piece of wood works better for this than lots of small pieces of wood (which tend to burn fast and hot).

I think you could build a rocket oven for this task, but I can't make any guarantees.  If you had even more mass inside the oven space, it would take longer to heat up, but it would be easier to keep the temperature steady.

I wonder if using metallurgical coal with a tiny DC blower would be better for temperature control.

We're talking very small amounts of coal, BTW, so I think the impact would be minimal.

How precisely does the oven need to hold 250?  A rocket oven can be designed/tweaked to run at a lower temperature but it's only as precise as your ability to keep the flame even.

Alternately, what about an old oven from a thrift shop?  Maybe the barrels would be too long...

In theory one could build a RMH that heats a mass to above the desired oven temp, and then holds the oven at a set temp by some mechanism to vary thermal transfer between mass and oven.

I like the idea of old steel engine blocks as a mass... allowing quite high temps in theory..

I haven't spent any time trying to figure out the rest of the design..

Assuming using your cooking stove is off limits due to fumes from the process. If you had a well ventilated space such as a garage to place it, working electric stoves are available inexpensively (I’ve even seen free giveaways) and would give decent control on temps during the process.