I used a milwakee heat gun, brick and old POS sheet metal "safe". Drilled a hole in the bottom and shoved the heat gun in there. Thermometer on the top. Worked great. I left it in my yard. In cold weather I had a rigid fiberglas shroud I slid over it to keep the heat regulated.
It worked...
I just worked up some 22" 338 lapua mag loads with Reloader 25. 300 SMK, Lapua brass, Winchester Magnum Rifle primers. Stupid low sds, but crappy velocities. At 2488 I had mild pressure signs. I'm going to try H1000.
This may help. Print it and see how it lines up. http://www.badgerordnance.com/wp-content/themes/buro/pdfs/M5_order_form.pdf
Yep- I'm the man, I know...
I found this interesting- unfortunately longest length is 24"
300 Winchester Magnum: How Does Barrel Length Change Velocity- A 16? 300 Win Mag? | Rifleshooter.com