I am trying to make a 25ft extension cord for my range. It is a 50 amp from what I understand.I will be plunging this into a 30 amp beaker the reason I am making this is it is going to be my power coating oven, that will only be used like one time a week or even less for about 1 to 2 hr at 350 degrees. I will not be using the top elements only the baking element. My questions is will it be safe to use the extension cord. I have 10-3 nm-b wire will that work for the cord.

Well, let's see now, apart from all the violations to the safety design of the oven you are creating, not including using a product for other than its intended use and then making an unapproved design change. Can this oven operate at 30 Amps?

How are you going to handle the ventilation for the oven? How long is the distance of the extension cord? Do you have the correct NEMA receptacle?

I'm sure there is more.

I am not sure if the oven will run at 30 amps. It's a Kenmore Model: 911.63275891
Serial: 8M232518Q it says for the power 7.6 kw 208 y/12 v 60 hz. a.c. 3-wire, 10.1 120/240v 60 hz a.c 3-wire. I am trying to make a 25 ft cord. Yes I have the right nema receptacle. My pain wire the 10-3 wire to the stove and make a long cord that goes into my Landry room so I can plug it into the drier outlet

Have you carefully read the listing with the powder coat materials..
It used to be some of these were more than combustible at higher temperatures.

As Don already indicated, you are taking on a lot of liability here...

This is not a DIY project you should tackle. Hire an electrician to run a new service to the stove. It will cost less than the materials to make such an extension cord that would be safe. A 50" 240 volt 30 amp cord sells for $150 and that will not do the job you want.