[Amps] Derating Dry Loads

[Mike & Becca Krzystyniak]

   I have Bird 8173 Coaxial load rated at 300 watts continuous.  

   I'm not that familiar with "dry RF loads" and I was wondering if these
loads can be derated for brief periods of higher power like oil filled loads
can?   

   I'm thinking of 1500 watts of CW dots for 5-10 seconds?  Just curious if
I should even try this, or maybe go buy a few hundred feet of RG-58 to put
in front of it...

Thanks in advance.

Mike K9MK